[FFmpeg-user] Different FrameMD5 when converting between loss-less encodings

Paul B Mahol onemda at gmail.com
Mon Nov 7 13:31:15 EET 2022

On 11/7/22, Tobias Rapp <t.rapp at noa-archive.com> wrote:
> On 07/11/2022 10:56, Paul B Mahol wrote:
>> On 11/7/22, Tobias Rapp <t.rapp at noa-archive.com> wrote:
>>> Hi,
>>> recently when testing I stumbled over the situation that a specific
>>> 10-bit YUV input file was encoded separately using two different
>>> loss-less encoders V210 and FFV1. When comparing the FrameMD5 checksum
>>> of both output files most of the checksums did match, but some of them
>>> where different (approx. 3% of the frames).
>>> When trying to reproduce the scenario with the attached batch script
>>> using a video source filter the resulting files even differ in every
>>> frame. My assumption would have been that the FrameMD5 checksums of both
>>> files would be the same, as they originate from the same input file and
>>> the intermediate encoding should be loss-less.
>>> Can someone give a hint where the differences come from? Is there some
>>> command-line option for bit-exactness missing, or is there something
>>> going wrong in the decoder/encoders?
>> The v210 encoder or decoder is buggy. Strange that both C and asm is
>> buggy.
>> The first pixels at start and end of each scanline are wrong.
> When I replace "-vcodec v210" in the shell script with "-vcodec ffvhuff"
> it matches the output of FFV1. So yes, there seems to be an issue with
> v210 encoding or decoding in FFmpeg.
> Looking into the bugtracker, could this be related to ticket #8195 "v210
> encoding clips to 4-1019"?

Ah, probably yes, and yuvtestsrc gives you 0-1023 ramp

> Regards,
> Tobias
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