[FFmpeg-trac] #8443(undetermined:new): A/V drift when reencoding NTSC
FFmpeg
trac at avcodec.org
Fri Dec 27 04:26:31 EET 2019
#8443: A/V drift when reencoding NTSC
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Reporter: | Owner:
madscientist159 |
Type: defect | Status: new
Priority: normal | Component:
| undetermined
Version: unspecified | Resolution:
Keywords: | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
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Comment (by pdr0):
I don't follow you - did you mean on a longer sample, or "output.mp4" ?
What overlaid audio ? Are we looking at the same thing ?
To be clear - I'm looking at the audio track waveform, on the actual
track. Make sure view=> waveform drawing => waveforms on is checked. Not
the showwaves waveform burned into the video.
Since the audio tone occurs every second, and since the video framerate is
23.976fps (~ 41.7ms / frame) - you cannot express whole seconds perfectly
everytime (unlike something like 25.0 fps). So the audio waveform position
might be slightly off a few ms each flash - you should expect that since
it's not a integer multiple.
But I'm not seeing drifting in that 30s sample. Drifting implies
progressively worsening. This means the largest delta should be been first
and last. I'm seeing the expected fwe ms variation in relation to the
flash frame. If it's a bit to the left, it's a bit to the right a bit
later. Progressive drift implies always 1 direction
You need to check longer sample. If it eventually shift 1 frame by a
certain time
Another possible complication is blender might not be the best tool for
this either; it usually deals with image sequences. It can have problems
with long GOP formats with non linear seeks (sometimes frames get mixed
up)
--
Ticket URL: <https://trac.ffmpeg.org/ticket/8443#comment:11>
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