write.h File Reference

Detailed Description

Writer API.

Writers are part of para_audiod(1), para_write(1) and para_play(1). They represent data sinks which receive input via the buffer tree mechanism from their parent buffer tree node and consume input data without producing any output.

An instance of a writer is described by struct writer_node, whose buffer tree node writer_node::btrn is set up as a leaf node of the buffer tree, see buffer_tree.h.

The alsa and the ao writer defined in alsa_write.c and ao_write.c consume the data received from higher level buffer tree nodes by writing data to an audio device, employing the alsa and ao low level libraries. The file writer (see file_write.c) writes data to an output file instead.

The functions declared here are defined in write_common.c.

Functions
int	check_writer_arg_or_die (const char *wa, struct lls_parse_result **lprp)
const struct writer *	writer_get (int wid)
const char *	writer_name (int wid)
void	register_writer_node (struct writer_node *wn, struct btr_node *parent, struct sched *s)
int	get_btr_sample_rate (struct btr_node *btrn, int32_t *result)
int	get_btr_channels (struct btr_node *btrn, int32_t *result)
int	get_btr_sample_format (struct btr_node *btrn, int32_t *result)
void	print_writer_helps (bool detailed)

Data Structures
struct	writer_node
struct	writer

Function Documentation

check_writer_arg_or_die()

int check_writer_arg_or_die	(	const char *	wa,
		struct lls_parse_result **	lprp
	)

Check if the given string is a valid writer argument.

Parameters

wa	String of the form writer_name options.
lprp	Contains the parsed command line on success.

If the argument is NULL, the (configuration-dependent) default writer and no arguments are assumed. Otherwise, the function makes sure that the argument starts with the name of a supported writer and splits the remaining part of the argument. In the second step the thusly obtained arguments are passed to the configuration parser determined in the first step, returning the parse result via the second argument to the function.

Returns

On success, the positive writer ID is returned. Otherwise the function prints an error message and calls exit(3).

writer_get()

const struct writer* writer_get

(

int

wid

)

Return the writer structure from a writer ID.

Parameters

wid	If non-positive, a pointer to the default writer is returned.

Returns

Pointer to a (constant) struct writer.

Referenced by register_writer_node().

writer_name()

const char* writer_name

(

int

wid

)

Return name of the writer identified by a writer ID.

Parameters

wid	If non-positive, the name of the default writer is returned.

Returns

The returned buffer must not be freed by the caller.

Referenced by register_writer_node().

register_writer_node()

void register_writer_node	(	struct writer_node *	wn,
		struct btr_node *	parent,
		struct sched *	s
	)

Open a writer node and register the corresponding task.

Parameters

wn	The writer node to open.
parent	The parent btr node (the source for the writer node).
s	The scheduler instance to register the task to.

get_btr_sample_rate()

int get_btr_sample_rate	(	struct btr_node *	btrn,
		int32_t *	result
	)

Ask parent buffer tree nodes for the sample rate of the current stream.

Parameters

btrn	Where to start the search.
result	Filled in by this function.

Returns

Standard.

get_btr_channels()

int get_btr_channels	(	struct btr_node *	btrn,
		int32_t *	result
	)

Ask parent buffer tree nodes for the channel count of the current stream.

Parameters

btrn	See get_btr_sample_rate.
result	See get_btr_sample_rate.

Returns

Standard.

get_btr_sample_format()

int get_btr_sample_format	(	struct btr_node *	btrn,
		int32_t *	result
	)

Ask parent nodes for the number of bits per sample and the byte sex.

Parameters

btrn	See get_btr_sample_rate.
result	Contains the sample format as an enum sample_format type.

Returns

Standard.

print_writer_helps()

void print_writer_helps

(

bool

detailed

)

Print the help text of all writers to stdout.

Parameters

detailed

Whether to print the short or the detailed help.