[FFmpeg-devel] [PATCH] Mimic decoder

Ramiro Polla ramiro
Sat Mar 22 03:01:07 CET 2008


Mike Melanson wrote:
> Ramiro Polla wrote:
>> Hello,
>>>> ffmpeg -i mimic1-womenloveffmpeg.cam mimic1-womenloveffmpeg.mpg
>>> A few questions:
>>> 1) Why is the framerate 1000 frames/second?
>> The timestamps are given in ms. The frames come at random times, 
>> whenever MSN has finished sending the last one. The timestamps are 
>> non-monotonic, like in this example:
>> 4191196
>> 4191384
>> 4191453
>> 4191531
>> 4191597
>> 4193731
>> 4193798
>> 4193930
>> 4193997
>> 4194663
>> 4194721
>> 4195131
>> 4195863
> I trust that there are not actually several thousand encoded frames in
> those files. Is there any way to ask FFmpeg to skip over unchanged frames?

The timestamps for MSN Messenger are obtained with GetTickCount(). What 
I meant is that the delay between two images may vary immensely. I had 
this same problem with the VFW grabber.

Can FFmpeg pass the input frames to the output without caring for a 
framerate? (for formats that accept non-monotonic timestamps). As in 1 
frame in, 1 frame out...

>>> 2) Is there any way to enable the bitexact option so that output will be
>>> consistent across platforms?
>> Is there anything not bitexact in this decoder? I thought bitexact only 
>> mattered for encoders with date/time and version info...
> Bit exactness is a big problem whenever the letters 'D', 'C', and 'T'
> are involved. The results are different on x86_32 and PPC (similar, but
> not bit exact). For more:
>   http://guru.multimedia.cx/the-mpeg124-and-h26123-idct/

How do other codecs (like jpeg) deal with this issue when bitexact is 
asked for? When I grep for CODEC_FLAG_BITEXACT I don't get much results 
that seem to work around this.

Ramiro Polla

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