[FFmpeg-user] Please help with weird video problems

[Anatoly]

On Wed, 8 Feb 2023 14:46:04 +0300
Alexander Gribanov <sunrisecoder at gmail.com> wrote:

> ср, 8 февр. 2023 г. в 02:11, Anatoly <anatoly at kazanfieldhockey.ru>:
> 
> > On Tue, 7 Feb 2023 22:00:35 +0300
> > Alexander Gribanov <sunrisecoder at gmail.com> wrote:
> >  
> > > Hello!
> > >
> > > Here is a downloaded Facebook Livestream video which I'm trying to
> > > process:
> > >  
> > https://drive.google.com/file/d/1mVkQbzVSzhOlQbT2mB1J2yvPFV5kl5Dq/view?usp=share_link
> >  
> > >
> > > I can play it correctly in MPC-HC Media Player Classic, but when I
> > > try to add this video to Adobe Premiere 2022, there around 3:00:00
> > > position audio is about 40 seconds ahead of video...
> > >
> > > I tried to remux and re-encode this video using ffmpeg, it showed
> > > a lot of warnings like this:
> > > [aac @ 000001c1bfe68e40] env_facs_q 254 is invalid
> > >
> > > I tried different options like "-vsync cfr", "-fps_mode drop" and
> > > some other stuff which I don't remember already, but nothing
> > > helped :( In MPC-HC it was ok, but in Adobe Premiere still
> > > 40-seconds a/v unsync.
> > >
> > > I assume that the problem is with timestamps on the audio track.
> > >
> > > I would like to make using ffmpeg just a simple cfr video 29.97
> > > fps / audio 48kHz without any timestamp gaps and offsets.
> > >
> > > Could anybody please help me to understand how to analyze and
> > > diagnose such problems in such videos to be sure what the exact
> > > problem is?
> > >
> > > Could You please help me find the solution (i.e. options or
> > > subcommands to ffmpeg).
> > >
> > > Thank You very much in advance :)  
> >
> > Maybe re-encode it with constant framerate using 'framerate' filter?
> > ffmpeg -i in.mp4 -vf framerate=fps=29.97 -c:a copy -c:v libx264 -b:v
> > 800k out.mp4
> >  
> 
> Hello Anatoly!
> Thank You very much for the reply, but it didn't help, the problem
> remains :(
> 
> Any other ideas?
I took a deeper look at your file. It seems that aac audio stream
contains undecodable frames (by all decoders I have aac, aac_fixed,
libfdk_aac). And ffmpeg just drops undecodable audio parts instead of
silence them. This results in audio track becomes shorter than video and
out of sync. Mplayer handles this properly, playing audio in sync, but
with very short and rare audio droputs. But mencoder does same way as
ffmpeg.
I succeed transcoding this file with Handbrake https://handbrake.fr, I
have version 1.3.3 installed with FDK aac. This also results in short
audio dropouts like playing with Mplayer.