Hacker Guide/Demux

Description

The modules of 'demux' capability are designed to handle the different "file" formats. They usually come after the access in the modules chain.

The demux modules are working on the stream that is provided by the core input to it.

Technically, the demuxers are pulling data from the stream; data is not pushed by the access to the demux.

Examples of demuxers are WMV/ASF, Ogg or Mkv.

Write an demuxer module

To write an demuxer module, read the introduction to module writing.

Then, you should specify your module of being of demux type:

set_capability( "demux", 60 )  
set_category( CAT_INPUT )                                                                                                                                                                                  
set_subcategory( SUBCAT_INPUT_DEMUX )

Functions to implement

After implementing Open() and Close() functions, you will need to implement a few majors features that will be implemented by your functions.

As you can see include/vlc_demux.h, you should define:

• Demux, as in pf_demux
• Control, as in pf_control

After implementing those functions, you should assign them to the corresponding pf_ function.

Control

Prototype:

int         (*pf_control)( access_t *, int i_query, va_list args);

Control function is quite easy, the input core will query the module using this function with:

• A pointer to the module structure.
• An i_query parameter that can be of several type. We will cover afterward the most important on.
• A list of arguments, that depends on the i_query type.

Return:

If the query has succeeded, it should return VLC_SUCCESS. Else it should return VLC_EGENERIC (fail).

Control Query types

See include/vlc_demux.h

Demux

Prototype:

 int (*pf_demux)  ( demux_t * ); 

Demux function is quite easy, it pulls data from s* the pointer to the stream_t.

Return:

It should return 0 for EOF, something positive when success and something negative when fail to demux.

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