[FFmpeg-devel] MOV Muxer fix to respect the standard

[Larbi Joubala]

M?ns Rullg?rd a ?crit :
> "Fran?ois Revol" <revol at free.fr> writes:
>
>   
>>> Hi guys,
>>>
>>>     I recently found when I generated a mp4 file that this file 
>>> doesn't 
>>> totally respect the standard(ISO media file format 14496-12) in 
>>> particulary for the box 'hdlr'. The handler description(named in the 
>>> standard as 'name') must be a NULL-terminated string in UTF8 while in 
>>> the generated file I saw that the string is not NULL-terminated and 
>>> it 
>>> is preceded by its size while it is not specifies by the standard.
>>>     If you confirm that, I have joined within this mail a patch that 
>>> you 
>>> can apply.
>>>       
>> From what I recall, in many places MOV does use PASCAL strings (length 
>> + non \0), while MP4 changed this to be C strings (\0 terminated), 
>> which is about the only significant difference (sometimes I wondered if 
>> it's not just to crash MOV parsers).
>>
>> I don't have time, but you'll definitely want to check both QT and MP4 
>> specs for this.
>>     
>
> ISO 14496-12 says null-terminated string, and QT says "counted
> string", so they are incompatible.  Of course, any size/termination is
> unnecessary since the string is the last element of the box and the
> box size is known.  Fools writing specs again...
>
>   
Fortunaletly, the box size is known otherwise any MP4/3GP/MOVdemuxer 
will fail to parse a file. However, There is a problem if the MOV 
backend of libavformat really want to be fully compliant with the 
following standards ISO 14496-12 and MOV.
What I propose is to generate a correct 'hdlr' box depending on the file 
format: name handler with PASCAL strings for MOV files and C strings for 
3GP/MP4 files.

What do you think about this?

Larbi Joubala