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.

Detailed Description

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.