Re: [FFmpeg-devel] [PATCH v4 1/3] avcodec/jpeg2000dec: Add support for CAP and CPF markers

[WATANABE Osamu <owatanab@es.takushoku-u.ac.jp>]

According to the suggestions for v4, I have posted the patch set v5.

It is confirmed that the decoder with v5 passes all the conformance testing defined in ISO/IEC 15444-4. 

Best,
Osamu


> On Jul 31, 2024, at 6:39, Michael Niedermayer <michael@niedermayer.cc> wrote:
> 
> On Tue, Jul 30, 2024 at 10:22:37PM +0200, Tomas Hardin wrote:
>> fre 2024-07-26 klockan 23:29 +0200 skrev Michael Niedermayer:
>>> On Thu, Jul 25, 2024 at 05:06:04PM -0700, Pierre-Anthony Lemieux
>>> wrote:
>>>> On Thu, Jul 25, 2024 at 2:17?AM Tomas Hardin <git@haerdin.se>
>>>> wrote:
>>>>> 
>>>>> son 2024-07-21 klockan 14:07 +0900 skrev Pierre-Anthony Lemieux:
>>>>>> On Sat, Jul 20, 2024 at 5:12?PM Tomas Hardin <git@haerdin.se>
>>>>>> wrote:
>>>>>>> 
>>>>>>> tor 2024-07-18 klockan 23:10 +0900 skrev Pierre-Anthony
>>>>>>> Lemieux:
>>>>>>>> On Mon, Jul 15, 2024 at 10:33?PM Tomas Hardin
>>>>>>>> <git@haerdin.se>
>>>>>>>> wrote:
>>>>>>>>> 
>>>>>>>>> fre 2024-07-12 klockan 12:51 -0700 skrev Pierre-Anthony
>>>>>>>>> Lemieux:
>>>>>>>>>> On Thu, Jul 11, 2024 at 10:28?PM Tomas Hardin
>>>>>>>>>> <git@haerdin.se>
>>>>>>>>>> wrote:
>>>>>>>>>>> 
>>>>>>>>>>>> +            if (s->in_tile_headers == 1 && s->isHT
>>>>>>>>>>>> &&
>>>>>>>>>>>> (!s-
>>>>>>>>>>>>> Ccap15_b11))
>>>>>>>>>>>> +                av_log(s->avctx, AV_LOG_WARNING,
>>>>>>>>>>>> "COD
>>>>>>>>>>>> marker
>>>>>>>>>>>> is
>>>>>>>>>>>> found in HOMOGENEOUS HT set\n");
>>>>>>>>>>> 
>>>>>>>>>>> How bad is this and the other markers being present
>>>>>>>>>>> in this
>>>>>>>>>>> case?
>>>>>>>>>> 
>>>>>>>>>> At the very least, it means that signaling is
>>>>>>>>>> inconsistent
>>>>>>>>>> within
>>>>>>>>>> the
>>>>>>>>>> codestream since the standard states that:
>>>>>>>>>> """
>>>>>>>>>> The HOMOGENEOUS set is the set of HTJ2K codestreams
>>>>>>>>>> where:
>>>>>>>>>> ? none of the functional marker segments, e.g., COD,
>>>>>>>>>> COC,
>>>>>>>>>> RGN,
>>>>>>>>>> QCD,
>>>>>>>>>> QCC, and POC, are present in any
>>>>>>>>>> tile-part header; and
>>>>>>>>>> ? no PPT marker segment is present.
>>>>>>>>>> """
>>>>>>>>>> 
>>>>>>>>>> The point of signalling that a codestream is
>>>>>>>>>> "HOMOGENEOUS" is
>>>>>>>>>> to
>>>>>>>>>> allow
>>>>>>>>>> decoders to configure themselves solely based on
>>>>>>>>>> information
>>>>>>>>>> retrieved
>>>>>>>>>> entirely from the main header.
>>>>>>>>>> 
>>>>>>>>>> Since, AFAIK, FFMPEG does not rely on the HOMOGENEOUS
>>>>>>>>>> to
>>>>>>>>>> short-
>>>>>>>>>> circuit
>>>>>>>>>> configuration, incorrect HOMOGENEOUS signalling will
>>>>>>>>>> likely
>>>>>>>>>> not
>>>>>>>>>> impact
>>>>>>>>>> FFMPEG.
>>>>>>>>> 
>>>>>>>>> It could happen that information in tile headers
>>>>>>>>> contradict
>>>>>>>>> information
>>>>>>>>> in the main header, right? In such a case it sounds like
>>>>>>>>> we
>>>>>>>>> can't
>>>>>>>>> be
>>>>>>>>> sure which decode is the correct one.
>>>>>>>> 
>>>>>>>> Per the spec, the decoder uses the COD information in tile-
>>>>>>>> parts
>>>>>>>> over
>>>>>>>> the COD information in the header.
>>>>>>>> 
>>>>>>>> The issue here is that a decoder, upon seeing HOMOGENEOUS,
>>>>>>>> simply
>>>>>>>> does
>>>>>>>> not bother with looking for COD information in tile-parts,
>>>>>>>> thereby
>>>>>>>> missing critical information.
>>>>>>> 
>>>>>>> So it is actually perfectly legal? Then it seems this patch
>>>>>>> is
>>>>>>> wrong
>>>>>> 
>>>>>> What is not "illegal": the HOMOGENEOUS flag being equal to true
>>>>>> *and*
>>>>>> having COD marker segments in tile-parts.
>>>>>> 
>>>>>> This is what the patch detects.
>>>>>> 
>>>>>> FFMPEG can decode such illegal codestream. Other decoders might
>>>>>> not.
>>>>>> 
>>>>>> The question is: what should FFMPEG do? Should FFMPEG exit or
>>>>>> warn
>>>>>> and continue.
>>>>> 
>>>>> If the spec allows it but it's perhaps unadviced then warning
>>>>> about it
>>>>> seems reasonable
>>>> 
>>>> (I totally messed up my double negative. Repeat below. Sorry for
>>>> the confusion.)
>>>> 
>>>> What is "illegal": the HOMOGENEOUS flag being equal to true *and*
>>>> having COD marker segments in tile-parts.
>>>> 
>>>> This is what the patch detects.
>>>> 
>>>> FFMPEG can decode such illegal codestream. Other decoders might
>>>> not.
>>>> 
>>>> The question is: what should FFMPEG do? Should FFMPEG exit or warn
>>>> and continue.
>>> 
>>> Does such a codestream actually exist ? I mean is this just a
>>> hypothetical case
>>> or something existing ?
>> 
>> This is more to stem the stream before anything happens because we were
>> lax with parsing
> 
> If such files dont exist then being picky makes sense
> 
> thx
> 
> [...]
> -- 
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
> 
> You can kill me, but you cannot change the truth.
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