Nudge non-monotonic source DTS instead of crashing the mux - #353
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Sloppy source files (e.g. web remuxes with 1/1000 audio time bases) can carry duplicate or backwards DTS in their audio/subtitle streams. The copy path in _pump_source_streams muxed those packets verbatim, and the mp4 muxer hard-fails with 'non monotonically increasing dts', killing the whole job partway through. Track the last muxed DTS per output stream and nudge offending packets forward by one tick, mirroring what ffmpeg's CLI muxer does and what _clamp_pts_monotonic already does for the video stream. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Fixes #352.
Problem
_pump_source_streamsmuxes copied source packets verbatim. If the source audio (or subtitle) stream carries a duplicate/backwards DTS — common in web remuxes with 1/1000 audio time bases — the mp4 muxer hard-fails withnon monotonically increasing dts to muxerand the whole job dies, potentially hours in. Deterministic: same packet, same crash, every run.Fix
New
_mux_source_packethelper tracks the last muxed DTS per output stream and nudges an offending packet forward by one tick (pts pulled up alongside if needed), then logs a warning. This mirrors what ffmpeg's CLI muxer does with such files, and what_clamp_pts_monotonicalready does for the encoded video stream. Used by both the pump loop and_drain_source_streams' transcode flush.Per-stream state lives in
_setup_source_streamsnext to the rest of the pump state.Testing
test_pump_nudges_non_monotonic_dts(duplicate DTS 370390 — the real-world value from the file I hit this on — comes out 370390, 370391 with pts matched).tests/test_video_encoder_unit.py: 109 passed; the 3 failures (TestSharpening×2,TestEncodeBuffer) also fail on a clean checkout in my env (CPU-only torch, no CUDA) and are unrelated.🤖 Generated with Claude Code