Re: [FFmpeg-devel] [PATCH] avformat/framecrcenc: compute the checksum for side data

[Michael Niedermayer <michael@niedermayer.cc>]

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On Mon, May 27, 2024 at 09:20:55PM +0200, Michael Niedermayer wrote:
> On Mon, May 27, 2024 at 03:17:15PM -0300, James Almer wrote:
> > On 5/27/2024 3:11 PM, Michael Niedermayer wrote:
> > > On Mon, May 27, 2024 at 10:15:43AM +0200, Anton Khirnov wrote:
> > > > Quoting Michael Niedermayer (2024-04-27 02:36:23)
> > > > > This allows detecting issues in side data related code, same as what
> > > > > framecrc does for before already for packet data itself.
> > > > > 
> > > > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > > > > ---
> > > > 
> > > > I am against this patch. Checksumming side data is a fundamentally wrong
> > > > thing to do.
> > > 
> > > It, or something equivalent is neccessary for regression testing.
> > > (and it was you who asked also for the tests i run to be part of
> > >   fate. But here you object to it)
> > > 
> > > You know, not checking side data is not checking it so differences would then not be
> > > detected allowing for unintended changes to be introduced (aka bugs)
> > 
> > You have seen how much code is needed to get hashing to work for all targets
> > with some types,
> 
>  framecrcenc.c |   76 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 73 insertions(+), 3 deletions(-)
> 
> 70 more lines of code, in my patch
> 
> If we need another 70 to handle some corner cases, no idea if we do, thats
> still negligible
> 
> 
> > so it does feel like it's not the right thing to do.
> 
> I dont think i can follow that logic
> 
> 
> > ffprobe (and f_sidedata) are what should be used for actual integrity
> > checks.
> 
> ffprobe cannot test ffmpeg, ffmpeg is a seperate excutable
> 
> If you suggest that side data should not be tested in FFmpeg while packet.data
> should be tested. That position seems inconsistant to me
> 
> If you suggest that neither side data nor packet.data should be tested in FFmpeg
> iam confident that there would be a majority disagreeing.
> 
> f_sidedata is not at the output of ffmpeg so even if it could test it, it
> does not test the ffmpeg output.
> We also dont replace running md5sum and framecrc on ffmpeg output by a bitstream
> filter.
> 
> Again, there is need to test what comes out of FFmpeg, thats at the muxer level
> thats what framecrcenc does.

There is also an additional aspect
and that is efficiency or "time taken by all fate tests"
framecrcenc already has all the side data, it costs basically 0 time to print that

any ffprobe based check needs to run everything a 2nd time, so it will be slower

also ffprobe is only good for side data from the demuxer.
my patch tests all cases including side data from the encoder or any other
source that gets forwarded to the muxer in each testcase.

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Never trust a computer, one day, it may think you are the virus. -- Compn

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