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.
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