On 07/11/2022 12:31, Paul B Mahol wrote:
On 11/7/22, Tobias Rapp <[email protected]> wrote:
On 07/11/2022 10:56, Paul B Mahol wrote:
On 11/7/22, Tobias Rapp <[email protected]> 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
Found some related information in Technote 2162 from Apple, chapter
"Scheme B: 'Video-Range' Mapping with Unsigned Y´, Offset Binary Cb, Cr":
https://developer.apple.com/library/archive/technotes/tn2162/_index.html#//apple_ref/doc/uid/DTS40013070-CH1-TNTAG7-SCHEME_B___VIDEO_RANGE__MAPPING_WITH_UNSIGNED_Y____OFFSET_BINARY_CB__CR
There it mentions that these component values are "reserved as
synchronization signals and must not appear in a buffer".
But is this document normative for anything besides QuickTime? From what
I can find the v210 encoder is the only one that follows this value
restriction, others like the v410 encoder do not.
Regards,
Tobias
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