From 60d1a641ee85e40badbb37d5d8a97d27f3c4615d Mon Sep 17 00:00:00 2001
From: Your Name <you@example.com>
Date: Sun, 28 Jun 2026 09:12:28 -0400
Subject: [PATCH] feat: broken fixes lol

---
 tl/dev/media_server.py          |   9 ++
 tl/resources/public/css/app.css |   5 +
 tl/shadow-cljs.edn              |   7 +-
 tl/src/tl/db.cljs               |   5 +-
 tl/src/tl/events.cljs           |  70 +++++++++--
 tl/src/tl/marks.cljs            |  68 +++++++++++
 tl/src/tl/subs.cljs             |  70 ++++++-----
 tl/src/tl/views.cljs            | 203 +++++++++++++++++++-------------
 tl/test/tl/marks_test.cljs      |  96 +++++++++++++++
 9 files changed, 412 insertions(+), 121 deletions(-)
 create mode 100644 tl/test/tl/marks_test.cljs

diff --git a/tl/dev/media_server.py b/tl/dev/media_server.py
index 71ff5d6..ec1f6c8 100755
--- a/tl/dev/media_server.py
+++ b/tl/dev/media_server.py
@@ -20,15 +20,23 @@ import time
 
 PORT = int(os.environ.get("MEDIA_PORT", "8281"))
 ROOT = os.path.join(os.path.dirname(__file__), "..", "resources", "public")
+MEDIA_CACHE_CONTROL = os.environ.get("MEDIA_CACHE_CONTROL", "public, max-age=604800")
+MEDIA_EXTENSIONS = {".mp4", ".mov", ".m4v", ".webm"}
 
 
 class RangeHandler(http.server.SimpleHTTPRequestHandler):
     def __init__(self, *args, **kwargs):
         super().__init__(*args, directory=os.path.abspath(ROOT), **kwargs)
 
+    def is_cacheable_media(self, path=None):
+        path = path or self.translate_path(self.path)
+        return os.path.splitext(path)[1].lower() in MEDIA_EXTENSIONS
+
     def end_headers(self):
         self.send_header("Access-Control-Allow-Origin", "*")
         self.send_header("Accept-Ranges", "bytes")
+        if self.is_cacheable_media():
+            self.send_header("Cache-Control", MEDIA_CACHE_CONTROL)
         super().end_headers()
 
     def send_head(self):
@@ -59,6 +67,7 @@ class RangeHandler(http.server.SimpleHTTPRequestHandler):
         self.send_header("Content-Type", self.guess_type(path))
         self.send_header("Content-Range", f"bytes {start}-{end}/{size}")
         self.send_header("Content-Length", str(end - start + 1))
+        self.send_header("Last-Modified", self.date_time_string(os.fstat(f.fileno()).st_mtime))
         self.end_headers()
         f.seek(start)
         self._range = (f, start, end)  # consumed by copyfile override
diff --git a/tl/resources/public/css/app.css b/tl/resources/public/css/app.css
index 9939258..aef0fea 100644
--- a/tl/resources/public/css/app.css
+++ b/tl/resources/public/css/app.css
@@ -131,6 +131,11 @@ body { overflow: hidden; }
 .row-x:hover { color: #e66; border-color: #a44; }
 .add-mark { align-self: flex-start; color: #cfe3f5; border-color: #3a6ea5; }
 
+/* the point a clip-click will fill — make it obvious where focus is */
+.pt-input.active .pt-text, .pt-chip.active {
+  outline: 2px solid #5ab07a; outline-offset: 0;
+}
+
 /* point editor + autocomplete */
 .pt-input { position: relative; flex: 1 1 130px; display: inline-block; }
 .pt-text {
diff --git a/tl/shadow-cljs.edn b/tl/shadow-cljs.edn
index 532f0bc..14a7c6c 100644
--- a/tl/shadow-cljs.edn
+++ b/tl/shadow-cljs.edn
@@ -15,7 +15,12 @@
   8290 "target/browser-test"}
 
  :builds
- {:app
+ {:test
+  {:target    :node-test
+   :output-to "target/node-tests.js"
+   :ns-regexp "-test$"}
+
+  :app
   {:target     :browser
    :output-dir "resources/public/js/compiled"
    :asset-path "/js/compiled"
diff --git a/tl/src/tl/db.cljs b/tl/src/tl/db.cljs
index d7c5745..4c49812 100644
--- a/tl/src/tl/db.cljs
+++ b/tl/src/tl/db.cljs
@@ -67,7 +67,10 @@
    ;; transient view state (mutates while scrubbing/zooming)
    :view {:zoom          50           ; X zoom: pixels per SECOND (px/frame = zoom/fps)
           :row-h         28           ; Y zoom: track row height in px
-          :playhead      0.0          ; frames (media/display coordinate)
+          ;; playhead per timeline context (frames): keyed by the timeline-stack
+          ;; top, so each (sub)timeline remembers where its playhead was. :root
+          ;; is the main timeline.
+          :playheads     {}
           :playing?      false
           :selected-clip nil
           ;; resizable layout (relative): top region height as vh, video pane
diff --git a/tl/src/tl/events.cljs b/tl/src/tl/events.cljs
index 8d10caf..002eb0b 100644
--- a/tl/src/tl/events.cljs
+++ b/tl/src/tl/events.cljs
@@ -3,6 +3,7 @@
    [re-frame.core :as rf]
    [tl.db :as db]
    [tl.otio :as otio]
+   [tl.marks :as marks]
    [tl.storage :as storage]
    [ajax.core :as ajax]))
 
@@ -47,10 +48,14 @@
 ;; The <video> element is the clock (direct 1:1): it pushes its currentTime
 ;; (as frames) into :playhead. See tl.views/video-monitor.
 
+(defn- ctx-id [db] (or (last (get-in db [:marks :timeline-stack])) :root))
+
 (rf/reg-event-db
  ::set-playhead
  (fn [db [_ frames]]
-   (assoc-in db [:view :playhead] frames)))
+   ;; the video clock writes into the current context's slot, so expanding /
+   ;; collapsing doesn't clobber another timeline's remembered position
+   (assoc-in db [:view :playheads (ctx-id db)] frames)))
 
 (rf/reg-event-db
  ::set-playing
@@ -87,25 +92,65 @@
                                       (update-in db [:draft :rows]
                                                  #(into (subvec % 0 i) (subvec % (inc i))))))
 
+;; Which point a clicked clip fills. Set when a point input gains focus, kept
+;; (not cleared on blur) so a subsequent clip click in the timeline lands here.
+(rf/reg-event-db ::set-draft-active (fn [db [_ path]] (assoc-in db [:draft :active] path)))
+
+;; Drop a clicked clip into the active point, then advance: start -> end of the
+;; same row; end -> start of the next row (appended if needed). Lets you build a
+;; range, or a run of ranges, by clicking clips left to right.
+(rf/reg-event-db
+ ::draft-fill-point
+ (fn [db [_ [_ i slot :as path] point]]
+   (let [db (assoc-in db (into [:draft] path) point)]
+     (if (= :a slot)
+       (assoc-in db [:draft :active] [:rows i :b])
+       (-> db
+           (update-in [:draft :rows]
+                      (fn [rows] (cond-> rows
+                                   (not (get rows (inc i))) (conj {:a {:text ""} :b {:text ""}}))))
+           (assoc-in [:draft :active] [:rows (inc i) :a]))))))
+
 ;; --- nested timelines: expand an annotation / navigate back -------------
 ;; The timeline-stack is the breadcrumb trail. Expanding pushes an annotation
 ;; id; the top of the stack is the current context (see ::context-id).
 
-(rf/reg-event-db
+(defn- context-spans
+  "The current context's mark-group spans, or nil at the root / no timeline."
+  [db ctx]
+  (when (and (not= :root ctx) (get-in db [:marks :groups ctx]) (:timeline db))
+    (not-empty (marks/resolve-group (marks/clip-index (:timeline db))
+                                    (get-in db [:marks :groups]) ctx))))
+
+(defn- seek-fx
+  "A :tl/seek effect for the db's current context: restore its remembered
+  playhead (defaulting to the first span's start) and hand the view its spans."
+  [db]
+  (let [ctx   (ctx-id db)
+        spans (context-spans db ctx)
+        frame (get-in db [:view :playheads ctx] (or (:start (first spans)) 0))]
+    {:fps (get-in db [:timeline :fps]) :frame frame :spans spans}))
+
+(rf/reg-event-fx
  ::expand-annotation
- (fn [db [_ id]] (update-in db [:marks :timeline-stack] conj id)))
+ (fn [{:keys [db]} [_ id]]
+   (let [db (update-in db [:marks :timeline-stack] conj id)]
+     {:db db :tl/seek (seek-fx db)})))
 
-(rf/reg-event-db
+(rf/reg-event-fx
  ::collapse                                   ; the back button: pop one level
- (fn [db _] (update-in db [:marks :timeline-stack]
-                       (fn [s] (if (> (count s) 1) (pop s) s)))))
+ (fn [{:keys [db]} _]
+   (let [db (update-in db [:marks :timeline-stack]
+                       (fn [s] (if (> (count s) 1) (pop s) s)))]
+     {:db db :tl/seek (seek-fx db)})))
 
-(rf/reg-event-db
+(rf/reg-event-fx
  ::pop-to                                     ; a breadcrumb: truncate to that id
- (fn [db [_ id]]
-   (update-in db [:marks :timeline-stack]
-              (fn [s] (let [i (first (keep-indexed #(when (= id %2) %1) s))]
-                        (if i (subvec s 0 (inc i)) s))))))
+ (fn [{:keys [db]} [_ id]]
+   (let [db (update-in db [:marks :timeline-stack]
+                       (fn [s] (let [i (first (keep-indexed #(when (= id %2) %1) s))]
+                                 (if i (subvec s 0 (inc i)) s))))]
+     {:db db :tl/seek (seek-fx db)})))
 
 ;; --- authoring: create / delete annotations (persisted) -----------------
 
@@ -145,4 +190,5 @@
                      (update-in [:marks :timeline-stack]
                                 (fn [s] (let [s' (vec (take-while #(not (doomed %)) s))]
                                           (if (seq s') s' [:root])))))]
-     {:db db' :tl/save (:marks db')})))
+     ;; deleting may have popped the stack — restore the surviving context
+     {:db db' :tl/save (:marks db') :tl/seek (seek-fx db')})))
diff --git a/tl/src/tl/marks.cljs b/tl/src/tl/marks.cljs
index 078393f..cae2b0d 100644
--- a/tl/src/tl/marks.cljs
+++ b/tl/src/tl/marks.cljs
@@ -87,3 +87,71 @@
   "Earliest display frame across spans — the scroll/sort anchor. nil if empty."
   [spans]
   (when (seq spans) (reduce min (map :start spans))))
+
+(defn- overlaps?
+  "Do inclusive frame ranges [a0 a1] and [b0 b1] touch or overlap?"
+  [a0 a1 b0 b1]
+  (and (<= a0 b1) (>= a1 b0)))
+
+;; --- mark-group time <-> clip time ----------------------------------------
+;; A timeline IS a mark-group: the root is the trivial one ([0 duration]); an
+;; annotation is one nested inside it. Resolving a mark-group gives its spans, in
+;; order — its local timeline is those spans laid end to end (gaps between them
+;; do not exist locally). These pure fns are the whole translation between a
+;; mark-group's local time and the underlying clip/media time, at any depth.
+
+(defn group-length
+  "Total frames of a mark-group's local timeline."
+  [spans]
+  (reduce + 0 (map #(- (:end %) (:start %)) spans)))
+
+(defn media->group
+  "Local frame for media frame `mf`, or nil when mf lies in a gap between spans."
+  [spans mf]
+  (loop [acc 0 [s & more] (seq spans)]
+    (when s
+      (if (<= (:start s) mf (:end s))
+        (+ acc (- mf (:start s)))
+        (recur (+ acc (- (:end s) (:start s))) more)))))
+
+(defn group->media
+  "Media frame for local frame `lf` (clamped to the group's length)."
+  [spans lf]
+  (loop [acc 0 [s & more] (seq spans)]
+    (if s
+      (let [len (- (:end s) (:start s))]
+        (if (<= (max 0 lf) (+ acc len))
+          (+ (:start s) (- (max 0 lf) acc))
+          (recur (+ acc len) more)))
+      (:end (last spans)))))
+
+(defn pieces
+  "Local [lo hi] sub-intervals of the media interval [a b], clipped to each span
+  — so an underlying clip is drawn only where the group covers it, and a span
+  that stops short of the clip yields a trimmed end."
+  [spans a b]
+  (loop [acc 0 [s & more] (seq spans) out []]
+    (if (nil? s)
+      out
+      (let [lo (max a (:start s)) hi (min b (:end s))]
+        (recur (+ acc (- (:end s) (:start s))) more
+               (cond-> out (< lo hi) (conj [(+ acc (- lo (:start s)))
+                                            (+ acc (- hi (:start s)))])))))))
+
+(defn tracks-overlapping
+  "Set of track names of the video clips in clip-index `idx` whose media range
+  intersects ANY of `spans` — the union of the spans, not their bounding box.
+  A clip lying only in a gap between two separate spans is excluded (so two
+  marks A and C don't pull in a clip B sitting between them), while a single
+  range that genuinely covers A→C does include everything along the way."
+  [idx spans]
+  (->> (vals idx)
+       (filter (fn [{:keys [kind media-in duration]}]
+                 ;; a clip's last frame is media-in + duration - 1 (the next clip
+                 ;; starts at media-in + duration); using the exclusive end here
+                 ;; falsely picks up the clip that begins where a span ends.
+                 (and (= :video kind)
+                      (let [last-frame (+ media-in duration -1)]
+                        (some #(overlaps? media-in last-frame (:start %) (:end %)) spans)))))
+       (map :track)
+       set))
diff --git a/tl/src/tl/subs.cljs b/tl/src/tl/subs.cljs
index 469a142..248fcd1 100644
--- a/tl/src/tl/subs.cljs
+++ b/tl/src/tl/subs.cljs
@@ -11,8 +11,9 @@
 (rf/reg-sub ::tracks   :<- [::timeline] (fn [t] (:tracks t)))
 
 ;; --- authoring draft -----------------------------------------------------
-(rf/reg-sub ::draft    (fn [db] (:draft db)))
-(rf/reg-sub ::draft-at (fn [db [_ path]] (get-in db (into [:draft] path))))
+(rf/reg-sub ::draft        (fn [db] (:draft db)))
+(rf/reg-sub ::draft-at     (fn [db [_ path]] (get-in db (into [:draft] path))))
+(rf/reg-sub ::draft-active (fn [db] (get-in db [:draft :active])))   ; point a clip click fills
 
 ;; --- mark-groups / annotations ------------------------------------------
 (rf/reg-sub ::groups         (fn [db] (get-in db [:marks :groups])))
@@ -74,38 +75,43 @@
  (fn [[groups stack] _]
    (mapv (fn [gid] {:id gid :name (:name (groups gid) (name gid))}) stack)))
 
-;; Crop: when expanded into an annotation, its own spans define the visible
-;; window (time range) and the set of involved tracks. nil at the root.
+;; The current context's spans (its local timeline, in order) — nil at the root.
+;; This IS the mark-group being shown; the timeline lays these end to end.
 (rf/reg-sub
- ::crop
+ ::context-spans
  :<- [::groups] :<- [::clip-index] :<- [::context-id]
  (fn [[groups idx ctx] _]
    (when (and idx (not= :root ctx) (groups ctx))
-     (let [spans (marks/resolve-group idx groups ctx)]
-       (when (seq spans)
-         {:window [(reduce min (map :start spans)) (reduce max (map :end spans))]
-          :tracks (set (keep :track spans))})))))
+     (not-empty (marks/resolve-group idx groups ctx)))))
 
-;; Video tracks to render, filtered to the crop's involved tracks when expanded.
-;; (Audio is never shown.) Returns {:track ... :visible? bool} so the timeline
-;; can collapse — rather than drop — hidden rows and animate them out.
+;; The spans the timeline renders against. The root is the trivial mark-group
+;; [0 duration] (so media frames map to themselves); a nested annotation uses
+;; its own spans, laid end to end (gaps between them simply don't exist locally).
+(rf/reg-sub
+ ::view-spans
+ :<- [::context-spans] :<- [::duration]
+ (fn [[spans dur] _] (or spans [{:start 0 :end (or dur 0)}])))
+
+(rf/reg-sub ::view-frames :<- [::view-spans]
+            (fn [spans _] (marks/group-length spans)))   ; local timeline length
+
+;; Tracks whose clips actually fall inside the current mark-group (union of its
+;; spans) — at the root, all of them. nil track-set => show everything.
+(rf/reg-sub
+ ::crop-tracks
+ :<- [::clip-index] :<- [::context-spans]
+ (fn [[idx spans] _]
+   (when (seq spans) (marks/tracks-overlapping idx spans))))
+
+;; Video tracks to render, each flagged :visible? so the timeline can collapse —
+;; rather than drop — the rows that aren't part of the current mark-group.
 (rf/reg-sub
  ::visible-tracks
- :<- [::tracks] :<- [::crop]
- (fn [[tracks crop] _]
-   (let [tset (when (seq (:tracks crop)) (:tracks crop))]
-     (->> tracks
-          (filter #(= :video (:kind %)))
-          (mapv (fn [t] (assoc t :visible? (or (nil? tset) (contains? tset (:name t))))))))))
-
-;; View transform applied to the timeline: a frame offset (so the crop window's
-;; start sits at the left edge) and the visible span length in frames.
-(rf/reg-sub
- ::view-offset :<- [::crop]
- (fn [crop _] (if crop (first (:window crop)) 0)))
-(rf/reg-sub
- ::view-frames :<- [::crop] :<- [::duration]
- (fn [[crop dur] _] (if crop (- (second (:window crop)) (first (:window crop))) dur)))
+ :<- [::tracks] :<- [::crop-tracks]
+ (fn [[tracks tset] _]
+   (->> tracks
+        (filter #(= :video (:kind %)))
+        (mapv (fn [t] (assoc t :visible? (or (nil? tset) (contains? tset (:name t)))))))))
 
 ;; The annotation the playhead is currently "in" — the latest one whose anchor
 ;; we've reached. Drives the commentary scroll + highlight.
@@ -119,7 +125,15 @@
 ;; --- view state (frames in; views multiply by zoom for pixels) ---
 (rf/reg-sub ::zoom     (fn [db] (get-in db [:view :zoom])))      ; X: px per second
 (rf/reg-sub ::row-h    (fn [db] (get-in db [:view :row-h])))     ; Y: track row height px
-(rf/reg-sub ::playhead (fn [db] (get-in db [:view :playhead]))) ; frames
+
+;; Playhead — a MEDIA frame (the video clock) for the current context. A context
+;; with no remembered position defaults to the start of its first span, so a
+;; freshly-expanded mark-group begins at its own beginning.
+(rf/reg-sub ::playheads (fn [db] (get-in db [:view :playheads])))
+(rf/reg-sub
+ ::playhead
+ :<- [::playheads] :<- [::context-id] :<- [::view-spans]
+ (fn [[phs ctx spans] _] (get phs ctx (or (:start (first spans)) 0))))
 (rf/reg-sub ::playing? (fn [db] (get-in db [:view :playing?])))
 (rf/reg-sub ::top-h    (fn [db] (get-in db [:view :top-h])))    ; layout: top region height
 (rf/reg-sub ::video-w  (fn [db] (get-in db [:view :video-w]))) ; layout: video pane width
diff --git a/tl/src/tl/views.cljs b/tl/src/tl/views.cljs
index f0a0454..c5e6ffc 100644
--- a/tl/src/tl/views.cljs
+++ b/tl/src/tl/views.cljs
@@ -18,6 +18,10 @@
 (defonce video-el (atom nil))
 (defonce scroll-el (atom nil))
 (defonce following? (atom true))
+;; The current mark-group's spans (its local timeline), or nil at the root. Read
+;; by the clock + frame-step from those non-reactive call sites without
+;; subscribing; kept current by the timeline render and the :tl/seek fx.
+(defonce play-spans (atom nil))
 
 (defn- secs [frames fps] (/ frames fps))
 
@@ -29,12 +33,17 @@
         sec (js/Math.floor (mod s 60))]
     (str m ":" (when (< sec 10) "0") sec)))
 
+(defn- local-x
+  "Pixel x for a media frame in the current mark-group's local timeline."
+  [spans fps zoom mf]
+  (* (secs (or (marks/media->group spans mf) 0) fps) zoom))
+
 (defn- center-on-playhead!
-  "Scroll the timeline so `playhead` sits at the horizontal centre. `off` is the
-  crop offset in frames (0 at the root; the window start when expanded)."
-  [fps zoom off playhead]
+  "Scroll the timeline so `playhead` (a media frame) sits at the horizontal
+  centre, in the current mark-group's local coordinates."
+  [fps zoom spans playhead]
   (when-let [el @scroll-el]
-    (let [px     (* (secs (- playhead off) fps) zoom)
+    (let [px     (local-x spans fps zoom playhead)
           max-sl (max 0 (- (.-scrollWidth el) (.-clientWidth el)))
           target (-> (- px (/ (.-clientWidth el) 2)) (max 0) (min max-sl))]
       (set! (.-scrollLeft el) target))))
@@ -44,16 +53,24 @@
 ;; write :playhead directly — we just move the video and let it report back.
 (defn- seek-to-frame! [fps frames]
   (when-let [v @video-el]
-    (set! (.-currentTime v) (secs frames fps))))
+    (set! (.-currentTime v) (secs (max 0 frames) fps))))
 
 (defn- jump! [fps frame] (seek-to-frame! fps frame))
 
+;; A navigation event (expand/collapse/pop/delete) computes — from its new db —
+;; the destination context's remembered playhead and crop window, and hands them
+;; here to restore that (sub)timeline's position and confine playback to it.
+(rf/reg-fx :tl/seek
+           (fn [{:keys [fps frame spans]}]
+             (reset! play-spans spans)   ; nil at the root
+             (when fps (seek-to-frame! fps frame))))
+
 (defn- jump-and-scroll!
   "Jump (seek video + move playhead) AND scroll the timeline to center the frame."
   [fps frame]
   (jump! fps frame)
   (center-on-playhead! fps (or @(rf/subscribe [::subs/zoom]) 50)
-                       (or @(rf/subscribe [::subs/view-offset]) 0) frame))
+                       @(rf/subscribe [::subs/view-spans]) frame))
 
 ;; --- authoring draft (in app-db at :draft; nil = closed) -----------------
 ;; A point is {:text "..."} (a typed frame) or {:clip <id> :setup <s> :occ <n>
@@ -61,17 +78,20 @@
 ;; instant, b filled => a range.
 
 (defn- blank-row [] {:a {:text ""} :b {:text ""}})
-(defn- blank-draft [] {:name "" :content "" :color "#4e8fc2" :rows [(blank-row)]})
+(defn- blank-draft []
+  {:name "" :content "" :color "#4e8fc2" :rows [(blank-row)] :active [:rows 0 :a]})
 
 (defn- insert-clip!
-  "Clicking a clip while authoring appends a whole-clip range row (clip[0]→clip[-1])."
+  "Clicking a clip while authoring drops it into the active point: a start point
+  takes the clip's first frame (0), an end point its last frame (-1). The active
+  point then advances (see ::draft-fill-point)."
   [clip-id]
-  (let [{:keys [setup occ]} (some #(when (= clip-id (:clip-id %)) %)
-                                  @(rf/subscribe [::subs/clip-catalog]))]
-    (when setup
-      (rf/dispatch [::events/draft-conj-row
-                    {:a {:clip clip-id :setup setup :occ occ :frame 0}
-                     :b {:clip clip-id :setup setup :occ occ :frame -1}}]))))
+  (when-let [{:keys [setup occ]} (some #(when (= clip-id (:clip-id %)) %)
+                                       @(rf/subscribe [::subs/clip-catalog]))]
+    (let [path (or @(rf/subscribe [::subs/draft-active]) [:rows 0 :a])
+          end? (= :b (last path))]
+      (rf/dispatch [::events/draft-fill-point path
+                    {:clip clip-id :setup setup :occ occ :frame (if end? -1 0)}]))))
 
 ;; reverse of the form's row->mark: turn stored marks back into editor rows
 (defn- clip-point [cat clip frame]
@@ -95,7 +115,7 @@
 
 (defn- edit-draft [cat id {:keys [name content color marks]}]
   {:id id :name name :content (or content "") :color (or color "#4e8fc2")
-   :rows (mapv #(mark->row cat %) marks)})
+   :rows (mapv #(mark->row cat %) marks) :active [:rows 0 :a]})
 
 ;; forward: editor row -> a mark (for save + the live timeline preview)
 (defn- point->mp
@@ -122,8 +142,10 @@
   [fps dir]
   (when-let [v @video-el]
     (when-not (.-paused v) (.pause v))
-    (let [frame (js/Math.round (* (.-currentTime v) fps))]
-      (set! (.-currentTime v) (secs (max 0 (+ frame dir)) fps)))))
+    (let [spans (or (seq @play-spans) [{:start 0 :end js/Infinity}])
+          local (or (marks/media->group spans (* (.-currentTime v) fps)) 0)]
+      ;; step in local time, then translate back to the underlying media frame
+      (set! (.-currentTime v) (secs (marks/group->media spans (+ (js/Math.round local) dir)) fps)))))
 
 (defn- editable-target?
   "True for fields where Space should type a space, not toggle play."
@@ -167,8 +189,21 @@
         capture! (fn [n] (when n (reset! video-el n)))  ; stable id; ignore React's nils
         tick     (fn tick []
                    (when-let [v @video-el]
-                     (let [t (.-currentTime v)]
-                       (when (not= t @seen)   ; skip churn while paused/idle
+                     ;; The video is the frame source for the local timeline. With
+                     ;; one <video> and non-contiguous media, playing off the end
+                     ;; of a span means we must jump to the next span's media (or
+                     ;; stop at the end) — translation is pure (media->group); this
+                     ;; only acts at a span boundary, so within a span the video
+                     ;; just plays.
+                     (when-let [spans (seq @play-spans)]
+                       (let [mf (* (.-currentTime v) fps)]
+                         (when-not (marks/media->group spans mf)
+                           (if-let [nxt (seq (filter #(> % mf) (map :start spans)))]
+                             (set! (.-currentTime v) (secs (reduce min nxt) fps))
+                             (do (when-not (.-paused v) (.pause v))
+                                 (set! (.-currentTime v) (secs (reduce max (map :end spans)) fps)))))))
+                     (let [t (.-currentTime v)]   ; re-read (advanced/clamped above)
+                       (when (not= t @seen)       ; skip churn while paused/idle
                          (reset! seen t)
                          (rf/dispatch [::events/set-playhead (* t fps)]))))
                    (reset! raf (js/requestAnimationFrame tick)))]
@@ -310,9 +345,10 @@
 
 (defn annotation-lane
   "The annotation rows above the tracks. Annotations are packed into shared rows
-  (see assign-lanes); each row holds every annotation assigned to that lane.
-  Bars are positioned in display frames relative to the crop offset `off`."
-  [fps zoom off placed active]
+  (see assign-lanes); each row holds every annotation in that lane. Bars are laid
+  out in the current mark-group's local coordinates (`vspans`) via marks/pieces,
+  so they line up with the clips below."
+  [fps zoom vspans placed active]
   [:div
    (doall
     (for [[li items] (->> placed (group-by :lane) (into (sorted-map)))]
@@ -321,65 +357,68 @@
        (doall
         (for [{:keys [id name spans preview?] c :color} items]
           (let [color (or c "#4e8fc2")
-                on?   (= id active)]
+                on?   (= id active)
+                rects (mapcat #(marks/pieces vspans (:start %) (:end %)) spans)]
             ^{:key id}
             [:<>
              (doall
-              (for [[j s] (map-indexed vector spans)]
-                (let [left (* (secs (- (:start s) off) fps) zoom)
-                      w    (* (secs (- (:end s) (:start s)) fps) zoom)]
-                  ^{:key j}
-                  [:div.ann-bar
-                   {:title name
-                    :style {:left left :width (max 3 w)
-                            :background (cond preview? (str color "44") on? color :else (str color "80"))
-                            :border (str (if preview? "1px dashed " "1px solid ") color)}}])))
-             (when-let [a (some-> spans first :start)]
-               [:div.ann-bar-label {:style {:left (+ 4 (* (secs (- a off) fps) zoom))}} name])])))]))])
+              (for [[j [lo hi]] (map-indexed vector rects)]
+                ^{:key j}
+                [:div.ann-bar
+                 {:title name
+                  :style {:left (* (secs lo fps) zoom) :width (max 3 (* (secs (- hi lo) fps) zoom))
+                          :background (cond preview? (str color "44") on? color :else (str color "80"))
+                          :border (str (if preview? "1px dashed " "1px solid ") color)}}]))
+             (when-let [[lo _] (first rects)]
+               [:div.ann-bar-label {:style {:left (+ 4 (* (secs lo fps) zoom))}} name])])))]))])
 
-(defn clip-block [fps zoom off row-h authoring? {:keys [id name media-in duration] :as _clip}]
-  (let [left  (* (secs (- media-in off) fps) zoom)
-        width (max 1 (* (secs duration fps) zoom))]
-    [:div.clip {:style {:left left :width width :height (- row-h 2)
-                        :line-height (str (- row-h 2) "px")}
-                ;; while authoring, click a clip to drop it into the marks list
-                :class (when authoring? "clickable")
-                :on-mouse-down (when authoring?
-                                 (fn [e]
-                                   (.stopPropagation e)   ; don't start a scrub
-                                   (insert-clip! (keyword id))))}
-     name]))
+(defn clip-block
+  "An underlying clip drawn in local coordinates: one block per piece where the
+  current mark-group covers it (none if it falls entirely in a removed gap; a
+  trimmed width where a span stops short of the clip)."
+  [fps zoom vspans row-h authoring? {:keys [id name media-in duration]}]
+  (into [:<>]
+        (for [[i [lo hi]] (map-indexed vector (marks/pieces vspans media-in (+ media-in duration)))]
+          ^{:key i}
+          [:div.clip {:style {:left (* (secs lo fps) zoom)
+                              :width (max 1 (* (secs (- hi lo) fps) zoom))
+                              :height (- row-h 2) :line-height (str (- row-h 2) "px")}
+                      :class (when authoring? "clickable")
+                      :on-mouse-down (when authoring?
+                                       (fn [e]
+                                         (.stopPropagation e)   ; don't start a scrub
+                                         (.preventDefault e)     ; keep the focused point input from blurring
+                                         (insert-clip! (keyword id))))}
+           name])))
 
 (defn track-row
-  "A track lane. When cropped out of the current view it collapses to height 0
-  (CSS transitions the height) rather than vanishing, so tracks animate away."
-  [fps zoom off row-h authoring? track]
+  "A track lane. When it isn't part of the current mark-group it collapses to
+  height 0 (CSS transitions the height) rather than vanishing."
+  [fps zoom vspans row-h authoring? track]
   (let [vis? (:visible? track true)]
     [:div.track-row {:class (when-not vis? "collapsed")
                      :style {:height (if vis? row-h 0)}}
-     ;; clips render even while collapsing (overflow:hidden clips them) so the
-     ;; row's contents shrink away with it instead of blanking instantly
      (for [c (:clips track)]
-       ^{:key (:id c)} [clip-block fps zoom off row-h authoring? c])]))
+       ^{:key (:id c)} [clip-block fps zoom vspans row-h authoring? c])]))
 
 (defn- ev->frames
-  "Pointer clientX -> clamped timeline frame, relative to the content div
-  (whose bounding rect already accounts for horizontal scroll). `off`/`end`
-  are the visible window bounds in frames."
-  [content clientX zoom fps off end]
-  (let [px     (- clientX (.-left (.getBoundingClientRect content)))
-        frames (+ off (* (/ px zoom) fps))]
-    (-> frames (max off) (min end))))
+  "Pointer clientX -> a media frame: read the local frame under the cursor (the
+  content rect already accounts for scroll) and translate back through the
+  current mark-group."
+  [content clientX zoom fps vspans]
+  (let [px    (- clientX (.-left (.getBoundingClientRect content)))
+        local (max 0 (* (/ px zoom) fps))]
+    (marks/group->media vspans local)))
 
 (defn- begin-scrub!
   "mousedown on the timeline: seek to the click, then follow the mouse (even
   outside the element) until mouseup."
-  [content zoom fps off end ev]
+  [content zoom fps vspans ev]
   (.preventDefault ev)
   (let [to (fn [clientX]
              ;; just seek; the video clock reports back into :playhead (rAF),
              ;; so the red line and the picture can never disagree
-             (seek-to-frame! fps (ev->frames content clientX zoom fps off end)))
+             (seek-to-frame! fps (ev->frames content clientX zoom fps vspans)))
         move (fn [e] (to (.-clientX e)))
         up   (fn up [_]
                (.removeEventListener js/document "mousemove" move)
@@ -394,8 +433,7 @@
       (let [fps      @(rf/subscribe [::subs/fps])
             zoom     @(rf/subscribe [::subs/zoom])
             row-h    @(rf/subscribe [::subs/row-h])
-            off      @(rf/subscribe [::subs/view-offset])
-            vframes  @(rf/subscribe [::subs/view-frames])
+            vspans   @(rf/subscribe [::subs/view-spans])    ; current mark-group's local timeline
             playhead @(rf/subscribe [::subs/playhead])
             playing? @(rf/subscribe [::subs/playing?])
             anns     @(rf/subscribe [::subs/annotations])
@@ -423,10 +461,11 @@
                              (filterv (comp seq :spans))))   ; need a footprint to pack
             placed   (assign-lanes lane-anns)
             lane-h   (* 18 (lane-count placed))
-            end      (+ off vframes)
-            width    (* (secs vframes fps) zoom)]
+            width    (* (secs (marks/group-length vspans) fps) zoom)]
+        ;; keep the clock's playback clamp in sync with the visible mark-group
+        (reset! play-spans @(rf/subscribe [::subs/context-spans]))
         (when (and playing? @following?)
-          (r/after-render #(center-on-playhead! fps zoom off playhead)))
+          (r/after-render #(center-on-playhead! fps zoom vspans playhead)))
         [:div.timeline
          ;; fixed left gutter: setup (track) names, in lockstep with the rows
          ;; (collapsed tracks shrink here too so labels stay aligned)
@@ -442,14 +481,14 @@
          [:div.hscroll {:ref (fn [n] (reset! scroll-el n))
                         :on-wheel (fn [_] (reset! following? false))}
           [:div.content {:ref (fn [n] (reset! content n))
-                         :on-mouse-down (fn [e] (begin-scrub! @content zoom fps off end e))
+                         :on-mouse-down (fn [e] (begin-scrub! @content zoom fps vspans e))
                          :style {:width width}}
-           (let [x (* (secs (- playhead off) fps) zoom)]
+           (let [x (local-x vspans fps zoom playhead)]
              [:div.playhead {:style {:left x}}
               [:div.playhead-handle]])
-           [annotation-lane fps zoom off placed active]
+           [annotation-lane fps zoom vspans placed active]
            (for [t vtracks]
-             ^{:key (:id t)} [track-row fps zoom off row-h (some? d) t])]]]))))
+             ^{:key (:id t)} [track-row fps zoom vspans row-h (some? d) t])]]]))))
 
 ;; --- zoom + layout shell --------------------------------------------------
 
@@ -462,14 +501,15 @@
   "Set X zoom while keeping the playhead pinned to its on-screen position
   (Resolve-style: zoom around the playhead, not the left edge)."
   [z1]
-  (let [el  @scroll-el
-        fps @(rf/subscribe [::subs/fps])
-        ph  @(rf/subscribe [::subs/playhead])
-        off (or @(rf/subscribe [::subs/view-offset]) 0)
-        z0  @(rf/subscribe [::subs/zoom])]
+  (let [el    @scroll-el
+        fps   @(rf/subscribe [::subs/fps])
+        ph    @(rf/subscribe [::subs/playhead])
+        spans @(rf/subscribe [::subs/view-spans])
+        z0    @(rf/subscribe [::subs/zoom])]
     (rf/dispatch [::events/set-zoom z1])
     (when el
-      (let [target (max 0 (+ (.-scrollLeft el) (* (secs (- ph off) fps) (- z1 z0))))]
+      (let [lf     (or (marks/media->group spans ph) 0)
+            target (max 0 (+ (.-scrollLeft el) (* (secs lf fps) (- z1 z0))))]
         (r/after-render #(set! (.-scrollLeft el) target))))))
 
 (defn breadcrumbs
@@ -551,13 +591,16 @@
     (fn [path placeholder]
       (let [p          (or @(rf/subscribe [::subs/draft-at path]) {})
             fps        (or @(rf/subscribe [::subs/fps]) (/ 24000 1001))
+            active?    (= path @(rf/subscribe [::subs/draft-active]))
+            activate!  #(rf/dispatch [::events/set-draft-active path])
             set-point! (fn [v] (rf/dispatch [::events/draft-set path v]))]
         (if (:clip p)
           (let [dur (some-> @(rf/subscribe [::subs/clip-index]) (get (:clip p)) :duration)]
-            [:span.pt-chip
+            [:span.pt-chip {:class (when active? "active")}
              [:span.pt-chip-name (str (:setup p) " [" (:occ p) "]")]
              [:input.pt-frame {:type "number" :value (:frame p)
                                :title "frame within clip (-1 = last)"
+                               :on-focus activate!
                                :on-change #(rf/dispatch [::events/draft-set (conj path :frame)
                                                          (js/parseInt (.. % -target -value))])}]
              (when dur [:span.pt-dur (str "/" dur)])
@@ -571,9 +614,10 @@
                                                  :frame {:text (str (:frame s))}
                                                  :clip  {:clip (:clip-id s) :setup (:setup s)
                                                          :occ (:occ s) :frame 0}))))]
-            [:span.pt-input
+            [:span.pt-input {:class (when active? "active")}
              [:input.pt-text
               {:value text :placeholder placeholder
+               :on-focus activate!
                :on-change #(do (set-point! {:text (.. % -target -value)}) (reset! hi 0))
                :on-key-down (fn [e]
                               (case (.-key e)
@@ -632,7 +676,8 @@
      [:div.form-marks-label "Marks"]
      (doall (for [i (range (count (:rows d)))] ^{:key i} [mark-row i]))
      [:button.add-mark {:on-click #(rf/dispatch [::events/draft-conj-row (blank-row)])} "＋ add mark"]
-     [:div.form-hint "Tip: click a clip in the timeline to drop it in as a whole-clip range."]
+     [:div.form-hint "Tip: focus the start or end field, then click clips in the timeline — "
+      "start takes the clip's first frame, end its last. It auto-advances start→end."]
      [:div.form-actions
       [:button.save {:on-click #(save-draft! d)} "Save"]
       [:button.cancel {:on-click #(rf/dispatch [::events/close-draft])} "Cancel"]]]))
diff --git a/tl/test/tl/marks_test.cljs b/tl/test/tl/marks_test.cljs
new file mode 100644
index 0000000..0732cc7
--- /dev/null
+++ b/tl/test/tl/marks_test.cljs
@@ -0,0 +1,96 @@
+(ns tl.marks-test
+  (:require [cljs.test :refer-macros [deftest is testing]]
+            [tl.marks :as marks]))
+
+;; A tiny clip catalog laid out on the media axis (the shared timeline):
+;;   A 100–149   (track "A")   B 150–199   (track "B")   C 200–249   (track "C")
+;; A and C are separated by B. Each entry mirrors tl.otio/parse output
+;; (clip-index values carry :track + :kind alongside :media-in/:duration).
+(def idx
+  {:a {:media-in 100 :duration 50 :track "A" :kind :video}
+   :b {:media-in 150 :duration 50 :track "B" :kind :video}
+   :c {:media-in 200 :duration 50 :track "C" :kind :video}
+   :sfx {:media-in 100 :duration 150 :track "SFX" :kind :audio}})
+
+(defn span [s e] {:start s :end e})
+
+(deftest tracks-overlapping-single-range
+  (testing "a single A→C range covers everything in between, incl. B"
+    (is (= #{"A" "B" "C"}
+           (marks/tracks-overlapping idx [(span 100 249)])))))
+
+(deftest tracks-overlapping-separate-marks
+  (testing "two separate marks (A and C) skip a clip B sitting only in the gap"
+    (is (= #{"A" "C"}
+           (marks/tracks-overlapping idx [(span 100 149) (span 200 249)]))))
+  (testing "the gap clip B is genuinely excluded (regression: bounding-box bug)"
+    (is (not (contains? (marks/tracks-overlapping idx [(span 100 149) (span 200 249)])
+                        "B")))))
+
+(deftest tracks-overlapping-single-clip
+  (testing "one whole-clip span yields just that track"
+    (is (= #{"B"} (marks/tracks-overlapping idx [(span 150 199)])))))
+
+(deftest tracks-overlapping-touching-boundary
+  (testing "a span touching a clip's edge frame counts as overlapping"
+    (is (= #{"A" "B"} (marks/tracks-overlapping idx [(span 100 150)])))))
+
+(deftest tracks-overlapping-excludes-audio
+  (testing "audio tracks are never returned"
+    (is (not (contains? (marks/tracks-overlapping idx [(span 100 249)]) "SFX")))))
+
+;; --- resolve-marks: the span coordinates the crop is built from -----------
+
+(deftest range-mark-spans-the-two-points
+  (testing "a [A-start A-end] range resolves to one span over A's frames"
+    (let [spans (marks/resolve-marks idx {} #{} [[[:at :a 0] [:at :a -1]]])]
+      (is (= 1 (count spans)))
+      (is (= 100 (:start (first spans))))
+      (is (= 149 (:end (first spans)))))))     ; media-in + (duration-1)
+
+(deftest two-separate-marks-resolve-to-two-spans
+  (testing "marks A and C resolve to two disjoint spans (no B coverage)"
+    (let [spans (marks/resolve-marks idx {} #{}
+                                     [[[:at :a 0] [:at :a -1]]
+                                      [[:at :c 0] [:at :c -1]]])]
+      (is (= [[100 149] [200 249]]
+             (map (juxt :start :end) spans)))
+      ;; and the union of those spans must not pull in B's track
+      (is (= #{"A" "C"} (marks/tracks-overlapping idx spans))))))
+
+;; --- mark-group <-> clip time: the gapless local timeline -----------------
+;; A mark-group of [clip-A] then [clip-C], A=100–150 and C=200–250, with the
+;; B gap (150–200) removed: a 100-frame local timeline laid end to end.
+(def grp [{:start 100 :end 150} {:start 200 :end 250}])
+
+(deftest group-length-sums-spans
+  (is (= 100 (marks/group-length grp))))
+
+(deftest media->group-translates-and-drops-gaps
+  (testing "media frames map onto the gapless local axis"
+    (is (= 0   (marks/media->group grp 100)))
+    (is (= 50  (marks/media->group grp 150)))
+    (is (= 50  (marks/media->group grp 200)))   ; C's start sits right after A
+    (is (= 75  (marks/media->group grp 225))))
+  (testing "a media frame in the removed gap has no local position"
+    (is (nil? (marks/media->group grp 175)))))
+
+(deftest group->media-is-the-inverse
+  (is (= 100 (marks/group->media grp 0)))
+  (is (= 225 (marks/group->media grp 75)))
+  (testing "the seam never resolves into the removed gap (B's media, 150–200)"
+    (is (= 150 (marks/group->media grp 50)))    ; A's end
+    (is (= 201 (marks/group->media grp 51))))   ; one frame into C, not B
+  (testing "past the end clamps to the last span's end"
+    (is (= 250 (marks/group->media grp 999)))))
+
+(deftest pieces-lay-clips-end-to-end-and-trim
+  (testing "clips A and C render adjacent in local space; B (the gap) doesn't"
+    (is (= [[0 50]]   (marks/pieces grp 100 150)))   ; clip A
+    (is (= []         (marks/pieces grp 150 200)))   ; clip B — in the gap
+    (is (= [[50 100]] (marks/pieces grp 200 250))))  ; clip C, right after A
+  (testing "a span trimming a clip short yields a trimmed end, not the full clip"
+    (let [trimmed [{:start 100 :end 130}]]           ; only 30 frames of clip A
+      (is (= [[0 30]] (marks/pieces trimmed 100 150)))
+      (is (= 130 (marks/group->media trimmed 30))))))
+