[FFmpeg-trac] #8635(avcodec:closed): FFV1 not lossless when encoding RGB data (bgr0 pixel format)

[FFmpeg]

#8635: FFV1 not lossless when encoding RGB data (bgr0 pixel format)
-------------------------------------+-------------------------------------
             Reporter:               |                    Owner:
  JustAnotherArchivist               |
                 Type:  defect       |                   Status:  closed
             Priority:  normal       |                Component:  avcodec
              Version:  unspecified  |               Resolution:  invalid
             Keywords:  ffv1         |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
Changes (by JustAnotherArchivist):

 * status:  new => closed
 * resolution:   => invalid


Comment:

 Interesting, thank you. Since x11grab produces bgr0 output, I assumed that
 using the same pix_fmt throughout should be lossless. Indeed, the fourth
 byte is the difference between the streams:

 {{{
 $ ffmpeg -i rgb.mkv -c:v rawvideo -f rawvideo -pix_fmt bgr0 - 2>/dev/null
 | xxd | head -1
 00000000: f4f5 f6ff f4f5 f6ff f4f5 f6ff f4f5 f6ff  ................
 $ ffmpeg -i ffv1.mkv -c:v rawvideo -f rawvideo -pix_fmt bgr0 - 2>/dev/null
 | xxd | head -1
 00000000: f4f5 f600 f4f5 f600 f4f5 f600 f4f5 f600  ................
 }}}

 And with gbrp, the streams are identical:

 {{{
 $ ffmpeg -i rgb.mkv -c:v rawvideo -f rawvideo -pix_fmt gbrp - 2>/dev/null
 | md5sum
 79058c74ef8d9ff27483828ac57c10fe  -
 $ ffmpeg -i ffv1.mkv -c:v rawvideo -f rawvideo -pix_fmt gbrp - 2>/dev/null
 | md5sum
 79058c74ef8d9ff27483828ac57c10fe  -
 }}}

 Sorry for the noise. I got identical streams with bgr0 with all other
 lossless codecs and settings I tried (x264, x265, vp9, huffyuv, rawvideo),
 so it seemed reasonable to assume that it's a stable colour encoding. Very
 confusing that the "0" actually means undefined, not NUL bytes.

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Ticket URL: <https://trac.ffmpeg.org/ticket/8635#comment:3>
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