[vlc-devel] MPEG-21 File Format support for VLC: Please assist

Michael Grafl michi_1111 at yahoo.de
Fri Jun 25 07:40:21 CEST 2010


On 24/06/2010 22:51, Ilkka Ollakka wrote:
> On Thu, Jun 24, 2010 at 09:55:32PM +0200, Michael Grafl wrote:
>> Hello all,
> Hi,
>> I have attached the zipped version of the patch (unfortunately still
>> for VLC 1.0.0). Who is willing to help me refactor the module?
> Would be better to move developing against 1.1 or 1.2 asap.

Yes, I will move to 1.2.

>> Three important aspects for refactoring (from my point of view) are:
>> - General cleanup: I have based my implementation on the MP4 demux
>> module and many things are not important to the MP21 module (e.g.,
>> the drms files seem useless)
> How does the mpeg-21 format differs from mp4-format? Why not just extend
> mp4-demuxer as you seem to have really much in common code there.

The main difference is that the mp21 file format is not another video 
and audio file format, i.e., it does not specify any codecs. It is a 
wrapper format that structures arbitrary files and respective metadata. 
One use case is packing mp4 files of a music album together with cover 
art etc. into a single mp21 file.
The mp21 file format and the mp4 file format have a common base, the ISO 
Base Media File Format that defines the inner architecture and 
structure. Actually, my authoring tool (http://music-mp21.sf.net) 
creates files that are valid mp21 and mp4 files.
However, I think that having mp21 and mp4 in a single demuxer would make 
the code rather convoluted because we'd have to distinguish between mp4 
and mp21 compatible files nontheless. The main problem would be that mp4 
files could use mp21 features without beeing valid mp21 files.
Thus, from my point of view, they should get different demuxers.

Yes, it is a good idea to base the mp12 access module on the zip module 
and it will be adopted.

Best regards,

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