Difference between revisions of "Hacker Guide/Demux"

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{{Back to|Hacker Guide}}
 
== Description  ==
 
== Description  ==
  
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The modules of ''''demux'''' capability are designed to handle the different "file" formats. They usually come after the access in the modules chain.
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The modules of ''''demux'''' capability are designed to handle the different "file" formats, like [[AVI]] or [[MKV]]. They usually come after the [[{{#rel2abs:../Access}}|Access]] module in the modules chain, and create the different tracks, that are sent to the decoders.
  
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The '''demux''' modules are working on the stream that is provided by the core input to it.
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The '''demuxer''' modules are working on the ''input stream'' that is provided by the core input to them. It splits the input stream into the different tracks (called ''elementary streams'').
  
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Technically, the demuxers are pulling data from the stream; data is not pushed by the access to the demux.
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Technically, the demuxers are '''pulling data''' from the stream; data is not pushed by the access to the demux.  
  
 
Examples of demuxers are [[ASF|WMV/ASF]], [[Ogg]] or [[Mkv]].
 
Examples of demuxers are [[ASF|WMV/ASF]], [[Ogg]] or [[Mkv]].
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== Write an demuxer module  ==
 
== Write an demuxer module  ==
  
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To write an demuxer module, read the [[Documentation:Hacker's Guide/Module Writers Guide|introduction to module writing]].  
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To write an demuxer module, start by reading the [[{{#rel2abs:../How To Write a Module}}|introduction to module writing]].  
  
 
Then, you should specify your module of being of demux type:  
 
Then, you should specify your module of being of demux type:  
  
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  set_capability( "demux", 60 )
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  set_capability( "demux", 60 )
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  set_category( CAT_INPUT )                                                                                                                                                                                
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  set_category( CAT_INPUT )
 
  set_subcategory( SUBCAT_INPUT_DEMUX )
 
  set_subcategory( SUBCAT_INPUT_DEMUX )
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== Functions to implement  ==
 
== Functions to implement  ==
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After implementing Open() and Close() functions, you will need to implement a few majors features that will be implemented by your functions.  
 
After implementing Open() and Close() functions, you will need to implement a few majors features that will be implemented by your functions.  
  
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As you can see {{VLCSourceFile|name=include/vlc_demux.h}}, you should define:  
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As you can see {{VLCSourceFile|include/vlc_demux.h}}, you should define:  
 +
 
 +
*Demux, as in pf_demux
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*Control, as in pf_control
 +
 
 +
After implementing those functions, you should assign them to the corresponding pf_ function.<br>
 +
 
 +
=== Demux  ===
 +
 
 +
''Prototype'':
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 +
  int (*pf_demux)  ( demux_t * );
 +
 
 +
Demux function is quite easy, it pulls data from '''s*''' the pointer to the stream_t.
  
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*Demux, as in pf_demux
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''Return'':
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*Control, as in pf_control
 
  
 +
It should return 0 for EOF, something positive when success and something negative when fail to demux.
  
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After implementing those functions, you should assign them to the corresponding pf_ function.
 
  
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== Control  ==
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=== Control  ===
  
 
''Prototype'':  
 
''Prototype'':  
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Control function is quite easy, the input core will query the module using this function with:  
 
Control function is quite easy, the input core will query the module using this function with:  
  
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*A pointer to the module structure.
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*A pointer to the module structure.  
 
*An '''i_query''' parameter that can be of several type. We will cover afterward the most important on.  
 
*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.
 
*A list of arguments, that depends on the '''i_query''' type.
−
 
  
 
''Return'':  
 
''Return'':  
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If the query has succeeded, it should return VLC_SUCCESS. Else it should return VLC_EGENERIC (''fail'').  
 
If the query has succeeded, it should return VLC_SUCCESS. Else it should return VLC_EGENERIC (''fail'').  
  
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=== Control Query types  ===
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==== Control Query types  ====
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 +
See {{VLCSourceFile|include/vlc_demux.h}}<br>
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 +
== Useful primitives and types  ==
  
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See {{VLCSourceFile|name=include/vlc_demux.h}}
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When implementing a demux, you will need to work on a '''stream''' (''stream_t''), but also to create and control '''tracks''' (ES) (''es_out_id_t'').  
  
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''stream_t *'' is the input (multiplexed) byte stream.<br />
 +
''es_out_id_t *'' are the elementary streams, to hand to the decoder.
  
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== Demux ==
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=== Tracks / ES manipulation ===
  
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''Prototype'':
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Tracks in VLC are named '''ES''', as ''Elementary Streams''  
  
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  int (*pf_demux)  ( demux_t * );
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You will probably need
  
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Demux function is quite easy, it pulls data from '''s*''' the pointer to the stream_t.
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*es_out_Add
 +
*es_out_Send
 +
*es_out_Control
  
 +
See {{VLCSourceFile|include/vlc_es_out.h}} and {{VLCSourceFile|include/vlc_es.h}}
  
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''Return'':
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=== Stream manipulation  ===
  
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It should return 0 for EOF, something positive when success and something negative when fail to demux.
+
Stream manipulation can be done with a few functions
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*stream_Read
 +
*stream_Peek
 +
*stream_Control
 +
*stream_ReadLine
 +
*stream_Block
  
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See {{VLCSourceFile|include/vlc_stream.h}} for more information
  
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{{Documentation}}{{Container}}
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{{Hacker_Guide}}
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[[Category:Coding]]
 

Latest revision as of 06:37, 17 April 2019

← Back to Hacker Guide

Description

The modules of 'demux' capability are designed to handle the different "file" formats, like AVI or MKV. They usually come after the Access module in the modules chain, and create the different tracks, that are sent to the decoders.

The demuxer modules are working on the input stream that is provided by the core input to them. It splits the input stream into the different tracks (called elementary streams).

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, start by reading 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.

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.


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

Useful primitives and types

When implementing a demux, you will need to work on a stream (stream_t), but also to create and control tracks (ES) (es_out_id_t).

stream_t * is the input (multiplexed) byte stream.
es_out_id_t * are the elementary streams, to hand to the decoder.

Tracks / ES manipulation

Tracks in VLC are named ES, as Elementary Streams

You will probably need

  • es_out_Add
  • es_out_Send
  • es_out_Control

See include/vlc_es_out.h and include/vlc_es.h

Stream manipulation

Stream manipulation can be done with a few functions

  • stream_Read
  • stream_Peek
  • stream_Control
  • stream_ReadLine
  • stream_Block

See include/vlc_stream.h for more information

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