[FFmpeg-user] Audio delays in source Quicktime results in long audio

[Tim Nicholson]

On 25/10/12 04:05, Bob Maple wrote:
> Been compressing a bunch of source files at home into ProRes testing the
> longer mux and that's been working great.
> 
> One thing I'm now noticing however is that I wind up with longer audio
> on the compressed result by a couple of frames.
> 
> Most of these are DSLR movies (h264 Quicktime, both long-GOP and all
> I-frame) but I've had this Animation Quicktimes rendered out of After
> Effects as well.
> 
> If I look at the source files with MediaInfo, I see on the audio track:
> 
>   Delay relative to video : 42ms
> 
> The source file shows a duration of 26s 818ms for both the audio and
> video track.  But after run through ffmpeg, the audio track shows as 26s
> 966ms.. a bit more than just the 42ms of the delay, so not sure what is
> about either.  I presume (but don't know yet) that the resulting movie's
> audio is out of sync as well, but I need to create some better test
> files in order to tell for sure, all I've got right now are movies with
> a very reverby camera mic.
> 
> Is there an argument I'm missing or anything or is the Quicktime decoder
> just not aware of these tagged delays?
> 

Could it be that the interleave ratio means that at the end of the file
there is insufficient audio to maintain the ratio, so padding is added
to compensate, making the audio longer?


> [..]


-- 
Tim