Functions Shared by Encode and Decode

Basic shared functions
const char *	th_version_string (void)
	Retrieves a human-readable string to identify the library vendor and version.
ogg_uint32_t	th_version_number (void)
	Retrieves the library version number.
ogg_int64_t	th_granule_frame (void *_encdec, ogg_int64_t _granpos)
	Converts a granule position to an absolute frame index, starting at 0.
double	th_granule_time (void *_encdec, ogg_int64_t _granpos)
	Converts a granule position to an absolute time in seconds.
int	th_packet_isheader (ogg_packet *_op)
	Determines whether a Theora packet is a header or not.
int	th_packet_iskeyframe (ogg_packet *_op)
	Determines whether a theora packet is a key frame or not.
Functions for manipulating header data
void	th_info_init (th_info *_info)
	Initializes a th_info structure.
void	th_info_clear (th_info *_info)
	Clears a th_info structure.
void	th_comment_init (th_comment *_tc)
	Initialize a th_comment structure.
void	th_comment_add (th_comment *_tc, char *_comment)
	Add a comment to an initialized th_comment structure.
void	th_comment_add_tag (th_comment *_tc, char *_tag, char *_val)
	Add a comment to an initialized th_comment structure.
char *	th_comment_query (th_comment *_tc, char *_tag, int _count)
	Look up a comment value by its tag.
int	th_comment_query_count (th_comment *_tc, char *_tag)
	Look up the number of instances of a tag.
void	th_comment_clear (th_comment *_tc)
	Clears a th_comment structure.

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Function Documentation

void th_comment_add	(	th_comment *	_tc,
		char *	_comment
	)

Add a comment to an initialized th_comment structure.

Note:

Neither th_comment_add() nor th_comment_add_tag() support comments containing null values, although the bitstream format does support them. To add such comments you will need to manipulate the th_comment structure directly.

Parameters:

	_tc	The th_comment struct to add the comment to.
	_comment	Must be a null-terminated UTF-8 string containing the comment in "TAG=the value" form.

void th_comment_add_tag	(	th_comment *	_tc,
		char *	_tag,
		char *	_val
	)

Add a comment to an initialized th_comment structure.

Note:

Neither th_comment_add() nor th_comment_add_tag() support comments containing null values, although the bitstream format does support them. To add such comments you will need to manipulate the th_comment structure directly.

Parameters:

	_tc	The th_comment struct to add the comment to.
	_tag	A null-terminated string containing the tag associated with the comment.
	_val	The corresponding value as a null-terminated string.

void th_comment_clear

(

th_comment *

_tc

)

Clears a th_comment structure.

This should be called on a th_comment structure after it is no longer needed. It will free all memory used by the structure members.

Parameters:

_tc

The th_comment struct to clear.

void th_comment_init

(

th_comment *

_tc

)

Initialize a th_comment structure.

This should be called on a freshly allocated th_comment structure before attempting to use it.

Parameters:

_tc

The th_comment struct to initialize.

char* th_comment_query	(	th_comment *	_tc,
		char *	_tag,
		int	_count
	)

Look up a comment value by its tag.

Parameters:

	_tc	An initialized th_comment structure.
	_tag	The tag to look up.
	_count	The instance of the tag. The same tag can appear multiple times, each with a distinct value, so an index is required to retrieve them all. The order in which these values appear is significant and should be preserved. Use th_comment_query_count() to get the legal range for the _count parameter.

Returns:

A pointer to the queried tag's value. This points directly to data in the th_comment structure. It should not be modified or freed by the application, and modifications to the structure may invalidate the pointer.

Return values:

NULL

If no matching tag is found.

int th_comment_query_count	(	th_comment *	_tc,
		char *	_tag
	)

Look up the number of instances of a tag.

Call this first when querying for a specific tag and then iterate over the number of instances with separate calls to th_comment_query() to retrieve all the values for that tag in order.

Parameters:

	_tc	An initialized th_comment structure.
	_tag	The tag to look up.

Returns:

The number on instances of this particular tag.

ogg_int64_t th_granule_frame	(	void *	_encdec,
		ogg_int64_t	_granpos
	)

Converts a granule position to an absolute frame index, starting at 0.

The granule position is interpreted in the context of a given th_enc_ctx or th_dec_ctx handle (either will suffice).

Parameters:

	_encdec	A previously allocated th_enc_ctx or th_dec_ctx handle.
	_granpos	The granule position to convert.

Returns:

The absolute frame index corresponding to _granpos.

Return values:

-1

The given granule position was invalid (i.e. negative).

double th_granule_time	(	void *	_encdec,
		ogg_int64_t	_granpos
	)

Converts a granule position to an absolute time in seconds.

The granule position is interpreted in the context of a given th_enc_ctx or th_dec_ctx handle (either will suffice).

Parameters:

	_encdec	A previously allocated th_enc_ctx or th_dec_ctx handle.
	_granpos	The granule position to convert.

Returns:

The absolute time in seconds corresponding to _granpos. This is the "end time" for the frame, or the latest time it should be displayed. It is not the presentation time.

Return values:

-1

The given granule position was invalid (i.e. negative).

void th_info_clear

(

th_info *

_info

)

Clears a th_info structure.

This should be called on a th_info structure after it is no longer needed.

Parameters:

_info

The th_info struct to clear.

void th_info_init

(

th_info *

_info

)

Initializes a th_info structure.

This should be called on a freshly allocated th_info structure before attempting to use it.

Parameters:

_info

The th_info struct to initialize.

int th_packet_isheader

(

ogg_packet *

_op

)

Determines whether a Theora packet is a header or not.

This function does no verification beyond checking the packet type bit, so it should not be used for bitstream identification; use th_decode_headerin() for that. As per the Theora specification, an empty (0-byte) packet is treated as a data packet (a delta frame with no coded blocks).

Parameters:

_op

An ogg_packet containing encoded Theora data.

Return values:

	1	The packet is a header packet
	0	The packet is a video data packet.

int th_packet_iskeyframe

(

ogg_packet *

_op

)

Determines whether a theora packet is a key frame or not.

This function does no verification beyond checking the packet type and key frame bits, so it should not be used for bitstream identification; use th_decode_headerin() for that. As per the Theora specification, an empty (0-byte) packet is treated as a delta frame (with no coded blocks).

Parameters:

_op

An ogg_packet containing encoded Theora data.

Return values:

	1	The packet contains a key frame.
	0	The packet contains a delta frame.
	-1	The packet is not a video data packet.

ogg_uint32_t th_version_number

(

void

)

Retrieves the library version number.

This is the highest bitstream version that the encoder library will produce, or that the decoder library can decode. This number is composed of a 16-bit major version, 8-bit minor version and 8 bit sub-version, composed as follows:

 (VERSION_MAJOR<<16)+(VERSION_MINOR<<8)+(VERSION_SUBMINOR)

Returns:

the version number.

const char* th_version_string

(

void

)

Retrieves a human-readable string to identify the library vendor and version.

Returns:

the version string.