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

[James Almer <jamrial@gmail.com>]

On 5/27/2024 4:31 PM, Michael Niedermayer wrote:
> 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.

We could extend showinfo_bsf to print side data information.

> 
> thx
> 
> [...]
> 
> 
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