fix(dub): pass OmniVoice's ffmpeg to yt-dlp so URL merge works off PATH (#712) (#716)

Dubbing a video URL on Windows (v0.3.8) failed with 'You have requested merging
of multiple formats but ffmpeg is not installed.' The download format selector
pulls separate video+audio streams, so yt-dlp muxes them via ffmpeg
(merge_output_format=mp4) — but yt-dlp only checks PATH, while OmniVoice's ffmpeg
is typically a bundled Tauri sidecar / imageio-ffmpeg binary that isn't on PATH.

yt_download_sync now sets ydl_opts['ffmpeg_location'] = find_ffmpeg() (the same
resolver the rest of the dub pipeline uses) when ffmpeg is resolvable; if it
isn't, the key is omitted so yt-dlp falls back to PATH as before (no regression).
Tests assert the location is passed when resolved and omitted when not.

Co-authored-by: mergetest <test@local>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -124,6 +124,11 @@ across dub, generate, and design (a corrupt-binary failure no longer poses as
   "get a free token" link. (#657, #669)
 ### Fixed
 
+- **Dubbing a video URL no longer fails with "ffmpeg is not installed."** yt-dlp
+  downloads video and audio as separate streams and muxes them with ffmpeg, but
+  it only looked on PATH — so on Windows (where OmniVoice's ffmpeg is a bundled
+  sidecar / `imageio-ffmpeg` binary off PATH) the merge aborted before the dub
+  could start. yt-dlp is now pointed at the same ffmpeg OmniVoice resolves. (#712)
 - **A synth that succeeded no longer 500s because of a history-logging hiccup.**
   If the local database somehow missed schema init, recording the clip to
   generation history failed with *"no such table: generation_history"* and

backend/services/dub_pipeline.py

@@ -551,6 +551,15 @@ def yt_download_sync(
         "extractor_retries": 5,
         "skip_unavailable_fragments": True,
     }
+    # #712: the format selector above pulls separate video+audio streams, so
+    # yt-dlp muxes them via ffmpeg (merge_output_format=mp4). yt-dlp only looks
+    # for ffmpeg on PATH and aborts with "you have requested merging of multiple
+    # formats but ffmpeg is not installed" — but OmniVoice's ffmpeg is often a
+    # bundled Tauri sidecar / imageio-ffmpeg binary that isn't on PATH (common on
+    # Windows). Point yt-dlp at the exact ffmpeg we resolve so the merge works.
+    _ffmpeg_bin = find_ffmpeg()
+    if _ffmpeg_bin:
+        ydl_opts["ffmpeg_location"] = _ffmpeg_bin
     if progress_hook is not None:
         ydl_opts["progress_hooks"] = [progress_hook]
 

tests/test_dub_download_ffmpeg_location.py

@@ -0,0 +1,61 @@
+"""yt-dlp must merge video+audio with OmniVoice's ffmpeg, not just PATH (#712).
+
+The download format selector pulls separate streams, so yt-dlp muxes them via
+ffmpeg. yt-dlp only checks PATH and aborts ("you have requested merging of
+multiple formats but ffmpeg is not installed") when ffmpeg is a bundled sidecar
+/ imageio binary off PATH (common on Windows). yt_download_sync must pass the
+resolved ffmpeg as `ffmpeg_location`.
+"""
+import os
+import sys
+
+import pytest
+
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))), "backend"))
+
+from services import dub_pipeline  # noqa: E402
+
+
+class _FakeYDL:
+    captured: dict = {}
+
+    def __init__(self, opts):
+        type(self).captured = dict(opts)
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *a):
+        return False
+
+    def extract_info(self, url, download=True):
+        raise RuntimeError("stop after capturing opts")
+
+    def prepare_filename(self, info):
+        return "unused"
+
+
+def test_download_passes_resolved_ffmpeg_location(tmp_path, monkeypatch):
+    import yt_dlp
+
+    monkeypatch.setattr(dub_pipeline, "find_ffmpeg", lambda: "/opt/omnivoice/ffmpeg")
+    monkeypatch.setattr(yt_dlp, "YoutubeDL", _FakeYDL)
+    with pytest.raises(Exception):
+        dub_pipeline.yt_download_sync("https://youtu.be/abc", str(tmp_path))
+
+    assert _FakeYDL.captured.get("ffmpeg_location") == "/opt/omnivoice/ffmpeg", (
+        "yt-dlp must merge formats with OmniVoice's resolved ffmpeg, not just PATH (#712)"
+    )
+
+
+def test_download_omits_ffmpeg_location_when_unresolved(tmp_path, monkeypatch):
+    # If we can't resolve ffmpeg, don't pin a bogus location — let yt-dlp try
+    # PATH as before (no regression for users who have ffmpeg on PATH).
+    import yt_dlp
+
+    monkeypatch.setattr(dub_pipeline, "find_ffmpeg", lambda: None)
+    monkeypatch.setattr(yt_dlp, "YoutubeDL", _FakeYDL)
+    with pytest.raises(Exception):
+        dub_pipeline.yt_download_sync("https://youtu.be/abc", str(tmp_path))
+
+    assert "ffmpeg_location" not in _FakeYDL.captured