Hacker Guide/Access

Description

The modules of 'access' capability are designed to be the first and last elements of a modules chain.

Access input and output handles most of the basic I/O for VLC. They are usually protocols implementations (http, ftp,...) or devices access (Webcams, Capture cards).

We will discuss about 'input access' in this page.

Starting to write an access module

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

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

set_capability( "access", 60 )  
set_category( CAT_INPUT )                                                                                                                                                                                  
set_subcategory( SUBCAT_INPUT_ACCESS )

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_access.h, you should define:

• Seek, as in pf_seek
• Control, as in pf_control
• Read or Block

Your module can be of a 'Block' or a 'Read' type, depending on what you need to access.

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

Seek

Prototype:

int         (*pf_seek) ( access_t *, uint64_t );

The seeking function will be called whenever a seek is requested.

The arguments are a pointer to the module structure, and the requested position.

NB: Seeking function can be NULL, if it isn't possible to seek in the protocol or device.

Control

Prototype:

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

Read

Prototype:

ssize_t     (*pf_read) ( access_t *, uint8_t *, size_t );  /* Return -1 if no data yet, 0 if no more data, else real data read */

Block

Prototype:

block_t    *(*pf_block)( access_t * );                  /* return a block of data in his 'natural' size, NULL if not yet data or eof */