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

[pdr0]

On 2021-04-01 11:41, pdr0 wrote:
> 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 ?

Before the 'settb=1/720000,setpts=N*30030'? That wouldn't be appropriate
because I need to guarantee 
that the input is forced to 24000/1001fps cfr, first.
>

That's what -vf fps=24000/1001 does. It forces 24000/1001 CFR. Use it first

I'm sure it was mentioned in one of your other threads

-vf fps=24000/1001
pts_time:0.0417083
pts_time:0.0834167
pts_time:0.125125

normal MKV
pts_time:0.042
pts_time:0.083
pts_time:0.125 







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