[FFmpeg-devel] [PATCH v2] avcodec/pngenc: support writing iCCP chunks

[Andreas Rheinhardt]

Niklas Haas:
> On Fri, 11 Mar 2022 11:17:42 +0100 Niklas Haas <ffmpeg at haasn.xyz> wrote:
>> Oops. `-c copy` doesn't actually test the PNG writing code. Need to use
>> `-c png` instead. Fixed in v2.
> 
> Hmm, actually, even this doesn't work. I can comment out the iCCP
> writing code and the iCCP chunk still gets written, somehow. Even though
> the file hash is different from the `-c copy` case!
> 
> Any idea how to force a re-encode?

What makes you believe that an iCCP chunk gets written? Is it the size
of the framecrc output? The reason for this is that this is the output
of the decoded png frame and not the hash of the demuxed packet or the
output file. The latter is included in the
+7e412f6a9e2c7fcb674336e5c104518d *tests/data/fate/png-icc.image2.
Comparing +49398 tests/data/fate/png-icc.image2 and the relevant line
from V1 shows that there is indeed more output.
You could use -c copy on the encoded file; and you can also use ffprobe
to directly inspect the side data.

- Andreas