[FFmpeg-user] Decimal times to frame numbers

Carl Zwanzig cpz at tuunq.com
Fri Aug 20 18:39:42 EEST 2021

I hate to disagree with you, but....

On 8/19/2021 5:56 AM, Nicolas George wrote:
> No, it is the other way around: you should not be thinking about frame
> numbers, you should be thinking about timestamps.
Not necessarily....

> Timestamps are an inherent property of the frame, they will be preserved
> or converted by filters and storage. Frame numbers are not.
Frame numbers are not an internal property of a frame itself, but I'm sure 
you know that in production and editing environments*, nobody cares about a 
timestamp, they care that this frame is 3 seconds and 5 frames from that 
one, that the clip is 32 seconds and 13 frames long, or that a transition 
takes 19 frames. Frame numbers are ordinal from an arbitrary point.

And it's not relevant that they be "preserved by filters" because the don't 
exist in that context anyway- kind of like saying that 20 story building 
doesn't have a 13th floor; it surely does, even if it's labeled "14".

*which tend to be fixed rate, not variable

It's also quite a lot easier and more clear and precise to specify a point 
as 00:00:00.13 (the thirteenth frame interpreted at the current frame rate) 
than as 0.43377... (at 29.97); it will always be the 13th frame of the 
second and can't mean anything else.

So, yes, frame numbers are meaningful and commonly used. If ffmpeg only 
accepts decimal seconds, so be it, but that complicates matters for a fair 
few users and they're not likely to change to decimals for their daily work.



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