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codec.h File Reference

The shared libtheoradec and libtheoraenc C API. More...

#include <ogg/ogg.h>

Go to the source code of this file.

Data Structures

struct  th_img_plane
 A buffer for a single color plane in an uncompressed image. More...
struct  th_info
 Theora bitstream information. More...
struct  th_comment
 The comment information. More...
struct  th_quant_ranges
 A set of qi ranges. More...
struct  th_quant_info
 A complete set of quantization parameters. More...
struct  th_huff_code
 A Huffman code for a Theora DCT token. More...

Return codes

#define TH_EFAULT   (-1)
 An invalid pointer was provided.
#define TH_EINVAL   (-10)
 An invalid argument was provided.
#define TH_EBADHEADER   (-20)
 The contents of the header were incomplete, invalid, or unexpected.
#define TH_ENOTFORMAT   (-21)
 The header does not belong to a Theora stream.
#define TH_EVERSION   (-22)
 The bitstream version is too high.
#define TH_EIMPL   (-23)
 The specified function is not implemented.
#define TH_EBADPACKET   (-24)
 There were errors in the video data packet.
#define TH_DUPFRAME   (1)
 The decoded packet represented a dropped frame.

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.

Defines

#define _O_THEORA_CODEC_H_   (1)
#define TH_NHUFFMAN_TABLES   (80)
 The number of Huffman tables used by Theora.
#define TH_NDCT_TOKENS   (32)
 The number of DCT token values in each table.

Typedefs

typedef th_img_plane th_ycbcr_buffer [3]
 A complete image buffer for an uncompressed frame.
typedef th_comment th_comment
 The comment information.
typedef unsigned char th_quant_base [64]
 A single base matrix.

Enumerations

enum  th_colorspace { TH_CS_UNSPECIFIED, TH_CS_ITU_REC_470M, TH_CS_ITU_REC_470BG, TH_CS_NSPACES }
 The currently defined color space tags. More...
enum  th_pixel_fmt {
  TH_PF_420, TH_PF_RSVD, TH_PF_422, TH_PF_444,
  TH_PF_NFORMATS
}
 The currently defined pixel format tags. More...


Detailed Description

The shared libtheoradec and libtheoraenc C API.

You don't need to include this directly.


Define Documentation

#define _O_THEORA_CODEC_H_   (1)
 

#define TH_DUPFRAME   (1)
 

The decoded packet represented a dropped frame.

The player can continue to display the current frame, as the contents of the decoded frame buffer have not changed.

#define TH_EBADHEADER   (-20)
 

The contents of the header were incomplete, invalid, or unexpected.

#define TH_EBADPACKET   (-24)
 

There were errors in the video data packet.

#define TH_EFAULT   (-1)
 

An invalid pointer was provided.

#define TH_EIMPL   (-23)
 

The specified function is not implemented.

#define TH_EINVAL   (-10)
 

An invalid argument was provided.

#define TH_ENOTFORMAT   (-21)
 

The header does not belong to a Theora stream.

#define TH_EVERSION   (-22)
 

The bitstream version is too high.

#define TH_NDCT_TOKENS   (32)
 

The number of DCT token values in each table.

#define TH_NHUFFMAN_TABLES   (80)
 

The number of Huffman tables used by Theora.


Typedef Documentation

typedef struct th_comment th_comment
 

The comment information.

This structure holds the in-stream metadata corresponding to the 'comment' header packet. The comment header is meant to be used much like someone jotting a quick note on the label of a video. It should be a short, to the point text note that can be more than a couple words, but not more than a short paragraph.

The metadata is stored as a series of (tag, value) pairs, in length-encoded string vectors. The first occurrence of the '=' character delimits the tag and value. A particular tag may occur more than once, and order is significant. The character set encoding for the strings is always UTF-8, but the tag names are limited to ASCII, and treated as case-insensitive. See the Theora specification, Section 6.3.3 for details.

In filling in this structure, th_decode_headerin() will null-terminate the user_comment strings for safety. However, the bitstream format itself treats them as 8-bit clean vectors, possibly containing null characters, and so the length array should be treated as their authoritative length.

typedef unsigned char th_quant_base[64]
 

A single base matrix.

typedef th_img_plane th_ycbcr_buffer[3]
 

A complete image buffer for an uncompressed frame.

The chroma planes may be decimated by a factor of two in either direction, as indicated by th_info::pixel_fmt. The width and height of the Y' plane must be multiples of 16. They may need to be cropped for display, using the rectangle specified by th_info::pic_x, th_info::pic_y, th_info::pic_width, and th_info::pic_height. All samples are 8 bits.

Note:
The term YUV often used to describe a colorspace is ambiguous. The exact parameters of the RGB to YUV conversion process aside, in many contexts the U and V channels actually have opposite meanings. To avoid this confusion, we are explicit: the name of the color channels are Y'CbCr, and they appear in that order, always. The prime symbol denotes that the Y channel is non-linear. Cb and Cr stand for "Chroma blue" and "Chroma red", respectively.


Enumeration Type Documentation

enum th_colorspace
 

The currently defined color space tags.

See the Theora specification, Chapter 4, for exact details on the meaning of each of these color spaces.

Enumerator:
TH_CS_UNSPECIFIED  The color space was not specified at the encoder.

It may be conveyed by an external means.

TH_CS_ITU_REC_470M  A color space designed for NTSC content.
TH_CS_ITU_REC_470BG  A color space designed for PAL/SECAM content.
TH_CS_NSPACES  The total number of currently defined color spaces.

enum th_pixel_fmt
 

The currently defined pixel format tags.

See the Theora specification, Section 4.4, for details on the precise sample locations.

Enumerator:
TH_PF_420  Chroma decimation by 2 in both the X and Y directions (4:2:0).

The Cb and Cr chroma planes are half the width and half the height of the luma plane.

TH_PF_RSVD  Currently reserved.
TH_PF_422  Chroma decimation by 2 in the X direction (4:2:2).

The Cb and Cr chroma planes are half the width of the luma plane, but full height.

TH_PF_444  No chroma decimation (4:4:4).

The Cb and Cr chroma planes are full width and full height.

TH_PF_NFORMATS  The total number of currently defined pixel formats.


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.


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