[FFmpeg-devel] [PATCH] mov demuxer crashes on certain .jp2 files

[Jai Menon]

Hi,

On Wed, Dec 17, 2008 at 12:20 AM, Baptiste Coudurier
<baptiste.coudurier at gmail.com> wrote:
> Jai Menon wrote:
>> Hi,
>>
>> On Tue, Dec 16, 2008 at 2:20 PM, Baptiste Coudurier
>> <baptiste.coudurier at gmail.com> wrote:
>>> Hi,
>>>
>>> Jai Menon wrote:
>>>> Hi,
>>>>
>>>> The mov demuxer segfaults when parsing certain .jp2 files found at :
>>>>
>>>> http://samples.mplayerhq.hu/jpeg2000/j2kp4files_v1_2.zip/testfiles_jp2/*.jp2
>>>>
>>>> Attached patch fixes this issue.
>>>>
>>> Fixed in a slightly different way.
>>> We still need to figure out what is the best way to handle .jp2 and .mj2.
>>>
>>> My first feeling is that the decoder will need to support 'atom'
>>> structure so .jp2 can be used with image2 format, maybe it does already,
>>> I don't know.
>>
>> jp2 is defined in itu recommendation t.800 annex I and it has the same
>> box/atom structure.
>> there is a signature atom, ftyp, jp2h, jp2c and other not so important atoms.
>>
>>> .mj2 is ISO media with 'jp2h' atom in 'stsd', chunks of data are 'jp2c'
>>> atoms IIRC.
>>
>> from the motion jpeg2k (t.802) itu rec, section 4.3 :
>>
>> 4.3 JP2 inheritance and compatibility
>> .....
>> 2) The objects (boxes or atoms) required by the JP2 specification
>> shall also be present.
>> ....
>>
>> so isn't it better that jp2 be handled by the mov demuxer itself? this
>> would basically mean handling the jp2h and jp2c
>> atoms.
>
> Why ? Please explain.
> I gave you an idea why not: "so .jp2 can be used with image2 format"

I'm not quite sure I understand. Are you implying that the img2
demuxer feed the file data to the jpeg2k decoder and
the decoder handle parsing of the atoms or ...

> In any way, mov demuxer will pass 'jp2c' atoms to decoder, so decoder
> has to support atom structure in some way, I think adding support for
> other boxes is trivial.

But I don't see any entry in the table for the jp2c atom. For the
purposes of decoding, iirc the jp2h atom
isn't really important and the mov_read_extradata function can be
modified to just setup the streams and codec parameters and
ignore most of data in it for the time being.

The jp2c atom is just a monolithic jpeg2k codestream so the i'm not
sure if the decoder really needs to do anything complicated.
I was thinking along the lines of adding the jp2c tag to the parser
table and a new function, but it seems to me that the mov demuxer
requires that a moov atom be present. I think what is required is that
the function, say mov_read_j2k_codestream
read in the codestream and create a packet which can then be sent to
the decoder.
Is there something wrong with this approach?

-- 
Regards,

Jai