Parsers

Elements that cut a formless byte stream into frames. More...

Files
file	mpipe_parser.h
	Stream parser base element.

Data Structures
struct	mpipe_parser
	Base parser element structure. More...

Functions
int	mpipe_parser_init (struct mpipe_parser *parser, uint8_t id)
	Initialize a parser element.
int	mpipe_parser_change_state (struct mpipe_element *self, enum mpipe_state_change transition)
	Change state function for the base parser element.

Detailed Description

Elements that cut a formless byte stream into frames.

A parser sits where a stream stops being bytes and starts being frames. Its input is a file or a socket, which can say nothing about what it carries; its output is whole frames of a format the parser worked out by looking at them.

That asymmetry is why a parser is its own base rather than a transform. It cannot map its output back to an input capability, so it does not implement a capability crossing; it simply describes what it produces. And because the element upstream of it knows no format, the format event that arrives from there announces nothing at all - the parser is what turns it into a real announcement by substituting the capability it settled on before passing it downstream.

A parser also usually needs one buffer more than the stream in flight, to hold the frame it is still assembling.

Function Documentation

mpipe_parser_change_state()

int mpipe_parser_change_state	(	struct mpipe_element *	self,
		enum mpipe_state_change	transition )

#include <mpipe_parser.h>

Change state function for the base parser element.

On the PAUSED to READY transition this resets the negotiated pad caps back to ANY so a subsequent re-negotiation starts fresh. Derived parsers that override change_state must chain to this base function to inherit that behavior.

Parameters

self	Pointer to the Elements
transition	Transition state, see mpipe_state_change

Returns

0 on success, negative errno otherwise

mpipe_parser_init()

int mpipe_parser_init	(	struct mpipe_parser *	parser,
		uint8_t	id )

#include <mpipe_parser.h>

Initialize a parser element.

Initializes the base parser element structure, its sink and source pads and the default callbacks. A concrete parser calls it first from its own init, with the same id, and then overrides what it needs.

Parameters

parser	Pointer to the Parsers to initialize.
id	Unique element identifier.

Returns

0 on success, negative errno otherwise.