[FFmpeg-user] Rescuing inconsistent frame rate screen capture file?

[Simon Roberts]

I'm topposting here because I think this is in some sense another
question, but since the problem I'm trying to solve remains the same,
I figure the earlier question should be here for context.

Do individual frames in a libx264 stream (in an mp4 container) carry
timestamps, as distinct from perhaps "sequence numbers"? And if so,
can ffmpeg access them or give me access to them?

I'm wondering if I might be able to extract a series of individual
frames with their timestamp information (ideally in the filenames!) so
that I might be able to recreate "even tempered" frames from a source
that has radically varying frame rates.

On Thu, Jul 23, 2020 at 1:23 PM Simon Roberts
<simon at dancingcloudservices.com> wrote:
>
> Hi all, I have some video files (video only, no audio) that were
> recorded using ffmpeg to capture a computer screen. Unfortunately, it
> seems that the frame rate is somehow inconsistent. When I stretch it
> (almost four minutes overall!) to synchronize over the 38 minutes of
> the audio file which was captured simultaneously, but on a different
> machine, the middle part goes way out of sync, drifting ahead and
> behind at different points. We're not talking a few frames here
> either, but tens of seconds.
>
> So, I suppose I have two questions, the more important is whether
> there might be a way to have ffmpeg recreate a fixed frame rate,
> building in the necessary duplicate frames, or dropping frames, based
> on the *timestamps* on frames? I will say that I tried simply
> transcoding from the x264/mp4 original file to a prores_ks/mov file,
> but the inconsistency was not fixed.
>
> The secondary question is what might cause this (it's an x11grab input
> through libx264, and was using about 2.5 of the 4 cores the machine
> has.) and how might I know that it's failing while the recording is
> taking place?
>