sound stuff

clips/extraction.py

@@ -161,6 +161,18 @@ def _extract_stills(job, proxy_path, frames_dir, frames, root):
 MAX_RATE = 120  # a capture rate; past this the container is describing something else
 
 
+def probe_audio(path):
+    """The length of an uploaded sound in seconds, refusing a file with no audio."""
+    data = json.loads(_command(["ffprobe", "-v", "error", "-show_streams",
+                                "-show_format", "-of", "json", str(path)]))
+    if not any(s.get("codec_type") == "audio" for s in data.get("streams", [])):
+        raise ValueError("the uploaded file has no audio stream")
+    duration = float(data.get("format", {}).get("duration") or 0)
+    if duration <= 0:
+        raise ValueError("the sound's length is unknown")
+    return duration
+
+
 def probe(path):
     """What the upload is, as far as choosing a proxy rate goes.