On 2021-03-03 11:30, Mark Filipak (ffmpeg) wrote:
On 2021-03-03 05:58, Moritz Barsnick wrote:
On Tue, Mar 02, 2021 at 17:32:42 -0500, Mark Filipak (ffmpeg) wrote:
Thank you, Jim. To the best of my knowledge, rational is not a 'C' datatype.
No, but it is an ffmpeg data type, AVRational, as defined in
libavutil/rational.h, along with functions to operate on this type.
I need to know the dimension (or 'C' datatype) of TB as it is used in PTC
calculations.
Do you really need to know?
Do you really need to ask?
I've tried transcoding a 2:21:19 movie via this script:
SET prep23=settb=expr=1/720000,setpts=N*30030
SET cfr23=setpts=N*1001/24000/TB,fps=24000/1001
SET codecs=-codec:v libx265 -x265-params crf=16:qcomp=1.00 -codec:a copy
-codec:s copy -dn
ffmpeg -i i:\BDMV\STREAM\00303.m2ts -vf %prep23%,%cfr23% %codecs% test.mkv
pause
exit
I succeeded. So, the working filter pipeline time_base -- whatever it is -- must have higher
resolution than 32 bits. Why?
With TB = 1/(720000 ticks/s), for a 24.976fps output,
deltaPTS = (1001/24000 frames/s)/(1/(720000 ticks/s)) = 30030 ticks/frame
If working time_base (from the AVRational) has an effective resolution of int32 (i.e. +/-2147483647
ticks), then frames past 0:49:42 will be dropped.
If working time_base has an effective resolution of uint32 (i.e. 4294967295 ticks), then frames past
1:39:26 will be dropped.
I think that the successful transcode of a 2:21:19 video confirms that the working time_base is
sufficient. I suspect it's a float but of course I don't know that and I don't know its resolution.
Why 720000? TB = 1/(720000 ticks/s) guarantees that 'PTS's will be exact integers for a wide variety
of source and intermediate frame rates.
Of course the MKV output resolution is 1 milliseconds, but I'm essentially setting the pipeline's
resolution to 1.3[8..] microseconds.
You know, I've transcoded a great number of movies and many wind up VFR. I think that's bogus,
resulting from loss of pipeline resolution.
Has anyone actually encountered a professionally mastered source video that is
VFR. I haven't.
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