[FFmpeg-user] Why are PTS values different from what's expected?

[pdr0]

Mark Filipak (ffmpeg) wrote
> On 2021-04-01 07:13, Mark Filipak (ffmpeg) wrote:
>> The source is MKV. MKV has a 1/1000 TB, so any PTS variance should be
>> less than 0.1%.
>> 
>> The filter complex is thinned down to just this: settb=1/720000,showinfo
>> 
>> Here is selected lines from the showinfo report (with   ...comments):
>> 
>> [Parsed_showinfo_1 @ 00000247d719ef00] config in time_base: 1/720000,
>> frame_rate: 24000/1001
>>     ...So, deltaPTS (calculated: 1/TB/FR) should be 30030.
>> [Parsed_showinfo_1 @ 00000247d719ef00] n:   1 pts:  30240   ...should be
>> 30030
>> [Parsed_showinfo_1 @ 00000247d719ef00] n:   2 pts:  59760   ...should be
>> 60060
>> [Parsed_showinfo_1 @ 00000247d719ef00] n:   3 pts:  90000   ...should be
>> 90090
>> [Parsed_showinfo_1 @ 00000247d719ef00] n:   4 pts: 120240   ...should be
>> 120120
>> 
>> The PTS variance is 0.7%.
>> 
>> Why are PTS values different from what's expected?
>> 
>> Note: If I force deltaPTS via setpts=N*30030, then of course I get what's
>> expected.
>> 
>> Thanks. This is critical and your explanation is greatly appreciated!
>> Mark.
> 
> UPDATE
> 
> If I change the filter complex to this:
> 
> settb=1/720000,setpts=N*30030,fps=fps=48000/1001,showinfo
> 
> all my follow-on processing goes straight into the toilet.
> 
> Explanation of the factors in the filter complex:
> settb=1/720000   ...mandate 1.3[8..] ms time resolution
> setpts=N*30030   ...force the input to exactly 24000/1001fps cfr
> fps=fps=48000/1001   ...frame double
> 
> However, fps=fps=48000/1001 does more than just frame double. It resets TB
> to 20.8541[6..] ms time 
> resolution. Look:
> 
> [Parsed_showinfo_3 @ 000001413bf0ef00] config in time_base: 1001/48000,
> frame_rate: 48000/1001
> [Parsed_showinfo_3 @ 000001413bf0ef00] n:   0 pts:      0
> [Parsed_showinfo_3 @ 000001413bf0ef00] n:   1 pts:      1
> [Parsed_showinfo_3 @ 000001413bf0ef00] n:   2 pts:      2
> [Parsed_showinfo_3 @ 000001413bf0ef00] n:   3 pts:      3
> 
> Gee, I wish the fps filter documention said that it changes TB and sets
> deltaPTS to '1'.
> 
> My follow-on frame processing can't tolerate 20.8541[6..] ms time
> resolution -- that explains why my 
> mechanical frame gynmastics have been failing!
> 
> Explanation: My follow-on processing does fractional frame adjustment that
> requires at least 
> 8.341[6..] ms resolution.
> 
> Workaround: I can frame double by another method that's somewhat ugly but
> that I know works and 
> doesn't trash time resolution.

Did you try changing the order? ie. -vf fps first ?




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