Ferdi Scholten ferdi at sttc-nlp.nl
Fri Mar 1 00:40:23 EET 2024

> Hi, Ferdi,
> Thank you for the tip. I checked it against what I'm doing.
> The 'pts_time's that it returns do not correlate with the exact times 
> that are computed from frame counts. For example, pts_time=760.607200 
> should be exactly 760.3[364635..] (based on PTS=2854113 in a 
> 24/1.001fps video having timebase = 90kHz). That is from my 
> investigation into cutting/concatenation errors that I'm continuing to 
> work on. There truly is something amiss inside FFmpeg's computations.
> It would be welcome to have someone check my work. It's lonely work 
> and incredibly meticulous.
> --Mark.
Hi Mark

I have been following your work on this, and admire your persistence in it.
However I think this is also related to the type of codec and container 
that is used. Your work as far as I know is about Transport Streams. 
Those are different from X265 in an MP4 or MKV container.
For what I can check on my own is when using MP4 or MKV containers the 
times given for key frames with above command are exactly as specified 
when encoding the original video with given specific I-frame intervals.
When cutting or trimming a video in an MKV container (what I do 
regularly) on keyframes, I get a video with exactly the specific length 
of time in between those keyframes as a result. However, I have never 
checked the correctness of PTS etc. for those cut video's, as they were 
always exactly what I wanted.

However, for this topic it is more about teaching the topic starter 
about the limits of codec:copy and it's limits in extracting and 
inserting streams.

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