Wrong timecode output with matroska and 23.976fps CFR file. about ffms2 HOT 10 CLOSED

From kalle.blomster on February 01, 2010 14:20:03

Converting to v1 will lead to rounding inaccuracies and is pointless. MKV doesn't
have a fixed framerate so claiming that ffms sees two different framerates is
likewise pointless.

I don't know what you mean by "WRONG" either since you didn't specify (pastebin both
the generated v2 timecodes files if you want me to provide more details) but most
likely what you're seeing is the result of mkvmerge converting timestamps to
millisecond precision. Use a higher precision in mkvmerge if you want more accurate
timestamps.

Status: Invalid

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From hammered999 on February 02, 2010 13:10:37

Sure I'll provide more info. The video contained in the avi is as reported by ffdshow
23.976fps. So the timecode files I get from ffms are:

plain avi--> http://pastebin.com/f1b531500 plain avi-->mmg(mkvtoolnix)-->mkv--> http://pastebin.com/m44f296a9

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From hammered999 on February 02, 2010 13:14:26

To add to my previous post.

Sure mkv doesn't have fixed framerate but when the actual framerate of the stream is
constant shouldn't the duration of each frame in MKV be the same?

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From kalle.blomster on February 02, 2010 14:50:43

1000/(24000/1001) = 41.708333... milliseconds per frame. With the default timestamp
precision MKV stores timestamps that are accurate to one millisecond. Do you know
what "rounding" means?

In any case you're getting exactly what is stored in the container, no more, no less.
It's not a bug in ffms. If you want to file a bug against anyone, do it against the
MKV spec designers, but they are unlikely to listen to you. I don't really see what
you'd complain about anyway since the maximum error is +/- 0.5ms, and your monitor
most likely only redraws the image once every 16.333 milliseconds anyway.

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From hammered999 on February 03, 2010 12:43:22

Ok. I finally got it. FFMS works as it should, it just is a limitation(?) of the
matroska spec. Of course, I am not able to see the difference between 23.976 and
23.809. The thing is that I just want it to reported "correctly". What I mean is this:

plain avi(23.976fps)-->mmg-->remuxed to mkv-->open through a simple avs-->x264-->raw
h264 file-->mmg(using the raw file and the timecodes from ffms)-->reencoded mkv

When I play/examine the "reencoded mkv" every player/tool reports the fps as 23.809.

So is there any chance to "fix" this in ffms, to make the timecode as 23.976 in this
cases(I ask it as a feature request obviously)
Or would I have better luck asking the mkvtoolnix guy to handle this kind of timecode
files as "23.976"?

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From hammered999 on February 03, 2010 12:44:53

@my previous post

-->open through a simple avs-->

should be:
-->open through a simple avs using ffms-->

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From kalle.blomster on February 05, 2010 11:22:49

It's already been fixed in SVN. If you want it right now use assumefps() in Avisynth.

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From hammered999 on February 06, 2010 02:51:20

I've built r279 . Yes it reports to Avisynth that the stream is "23.976" but I was
refering to the timecode file. The timecode file still has "23.809" and "24.390" and
that's now ideal when I mux the raw stream. Every tool/player recognises the new-mkv
file as "23.809" fps.(the video part)

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From hammered999 on February 06, 2010 04:49:38

"that's now ideal when I" --> "that's not ideal when I"

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From kalle.blomster on February 08, 2010 15:12:26

You can't get precision that isn't there. If you know the file is supposed to be
exactly 23.976, mux it as that with a v1 timecodes file (or no timecodes file at
all). Then demux a v2 timecodes file using mkvextract, take a good hard look at it
and consider the meaning of life for a while.

(hint: there is a mkvmerge parameter that can change the timestamp precision if that
is what you really want)

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