libtheora: theora.h File Reference

# theora.h File Reference

The libtheora pre-1.0 legacy C API. More...

`#include <stddef.h>`
`#include <ogg/ogg.h>`

Go to the source code of this file.

## Data Structures
struct | yuv_buffer
| A YUV buffer for passing uncompressed frames to and from the codec. More...
struct | theora_info
| Theora bitstream info. More...
struct | theora_state
| Codec internal state and context. More...
struct | theora_comment
| Comment header metadata. More...
## Defines
#define | OC_FAULT -1
| General failure.
#define | OC_EINVAL -10
| Library encountered invalid internal data.
#define | OC_DISABLED -11
| Requested action is disabled.
#define | OC_BADHEADER -20
| Header packet was corrupt/invalid.
#define | OC_NOTFORMAT -21
| Packet is not a theora packet.
#define | OC_VERSION -22
| Bitstream version is not handled.
#define | OC_IMPL -23
| Feature or action not implemented.
#define | OC_BADPACKET -24
| Packet is corrupt.
#define | OC_NEWPACKET -25
| Packet is an (ignorable) unhandled extension.
#define | OC_DUPFRAME 1
| Packet is a dropped frame.
theora_control() codes
#define | TH_DECCTL_GET_PPLEVEL_MAX (1)
| Get the maximum post-processing level.
#define | TH_DECCTL_SET_PPLEVEL (3)
| Set the post-processing level.
#define | TH_ENCCTL_SET_KEYFRAME_FREQUENCY_FORCE (4)
| Sets the maximum distance between key frames.
#define | TH_DECCTL_SET_GRANPOS (5)
| Set the granule position.
#define | TH_ENCCTL_SET_QUANT_PARAMS (2)
| Sets the quantization parameters to use.
#define | TH_ENCCTL_SET_VP3_COMPATIBLE (10)
| Disables any encoder features that would prevent lossless transcoding back to VP3.
#define | TH_ENCCTL_GET_SPLEVEL_MAX (12)
| Gets the maximum speed level.
#define | TH_ENCCTL_SET_SPLEVEL (14)
| Sets the speed level.
## Enumerations
enum | theora_colorspace { OC_CS_UNSPECIFIED, OC_CS_ITU_REC_470M, OC_CS_ITU_REC_470BG, OC_CS_NSPACES }
| A Colorspace. More...
enum | theora_pixelformat { OC_PF_420, OC_PF_RSVD, OC_PF_422, OC_PF_444 }
| A Chroma subsampling. More...
## Functions
const char * | theora_version_string (void)
| Retrieve a human-readable string to identify the encoder vendor and version.
ogg_uint32_t | theora_version_number (void)
| Retrieve a 32-bit version number.
int | theora_encode_init (theora_state *th, theora_info *ti)
| Initialize the theora encoder.
int | theora_encode_YUVin (theora_state *t, yuv_buffer *yuv)
| Submit a YUV buffer to the theora encoder.
int | theora_encode_packetout (theora_state *t, int last_p, ogg_packet *op)
| Request the next packet of encoded video.
int | theora_encode_header (theora_state *t, ogg_packet *op)
| Request a packet containing the initial header.
int | theora_encode_comment (theora_comment *tc, ogg_packet *op)
| Request a comment header packet from provided metadata.
int | theora_encode_tables (theora_state *t, ogg_packet *op)
| Request a packet containing the codebook tables for the stream.
int | theora_decode_header (theora_info *ci, theora_comment *cc, ogg_packet *op)
| Decode an Ogg packet, with the expectation that the packet contains an initial header, comment data or codebook tables.
int | theora_decode_init (theora_state *th, theora_info *c)
| Initialize a theora_state handle for decoding.
int | theora_decode_packetin (theora_state *th, ogg_packet *op)
| Input a packet containing encoded data into the theora decoder.
int | theora_decode_YUVout (theora_state *th, yuv_buffer *yuv)
| Output the next available frame of decoded YUV data.
int | theora_packet_isheader (ogg_packet *op)
| Report whether a theora packet is a header or not This function does no verification beyond checking the header flag bit so it should not be used for bitstream identification; use theora_decode_header() for that.
int | theora_packet_iskeyframe (ogg_packet *op)
| Report whether a theora packet is a keyframe or not.
int | theora_granule_shift (theora_info *ti)
| Report the granulepos shift radix.
ogg_int64_t | theora_granule_frame (theora_state *th, ogg_int64_t granulepos)
| Convert a granulepos to an absolute frame index, starting at 0.
double | theora_granule_time (theora_state *th, ogg_int64_t granulepos)
| Convert a granulepos to absolute time in seconds.
void | theora_info_init (theora_info *c)
| Initialize a theora_info structure.
void | theora_info_clear (theora_info *c)
| Clear a theora_info structure.
void | theora_clear (theora_state *t)
| Free all internal data associated with a theora_state handle.
void | theora_comment_init (theora_comment *tc)
| Initialize an allocated theora_comment structure.
void | theora_comment_add (theora_comment *tc, char *comment)
| Add a comment to an initialized theora_comment structure.
void | theora_comment_add_tag (theora_comment *tc, char *tag, char *value)
| Add a comment to an initialized theora_comment structure.
char * | theora_comment_query (theora_comment *tc, char *tag, int count)
| Look up a comment value by tag.
int | theora_comment_query_count (theora_comment *tc, char *tag)
| Look up the number of instances of a tag.
void | theora_comment_clear (theora_comment *tc)
| Clear an allocated theora_comment struct so that it can be freed.
int | theora_control (theora_state *th, int req, void *buf, size_t buf_sz)
| Encoder control function.

## Detailed Description

The libtheora pre-1.0 legacy C API.

## Introduction

This is the documentation for the libtheora legacy C API, declared in the theora.h header, which describes the old interface used before the 1.0 release. This API was widely deployed for several years and remains supported, but for new code we recommend the cleaner API declared in theoradec.h and theoraenc.h.

libtheora is the reference implementation for Theora, a free video codec. Theora is derived from On2's VP3 codec with improved integration with Ogg multimedia formats by Xiph.Org.

## Overview

This library will both decode and encode theora packets to/from raw YUV frames. In either case, the packets will most likely either come from or need to be embedded in an Ogg stream. Use libogg or liboggz to extract/package these packets.

## Decoding Process

Decoding can be separated into the following steps:

1. initialise theora_info and theora_comment structures using theora_info_init() and theora_comment_init():

        theora_info     info;
        theora_comment  comment;

        theora_info_init(&info);
        theora_comment_init(&comment);

2. retrieve header packets from Ogg stream (there should be 3) and decode into theora_info and theora_comment structures using theora_decode_header(). See Identifying Theora Packets for more information on identifying which packets are theora packets.

        int i;
        for (i = 0; i < 3; i++)
        {
          (get a theora packet "op" from the Ogg stream)
          theora_decode_header(&info, &comment, op);
        }

3. initialise the decoder based on the information retrieved into the theora_info struct by theora_decode_header(). You will need a theora_state struct.

        theora_state state;

        theora_decode_init(&state, &info);

4. pass in packets and retrieve decoded frames! See the yuv_buffer documentation for information on how to retrieve raw YUV data.

        yuf_buffer buffer;
        while (last packet was not e_o_s) {
          (get a theora packet "op" from the Ogg stream)
          theora_decode_packetin(&state, op);
          theora_decode_YUVout(&state, &buffer);
        }

### Identifying Theora Packets

All streams inside an Ogg file have a unique serial_no attached to the stream. Typically, you will want to

- retrieve the serial_no for each b_o_s (beginning of stream) page encountered within the Ogg file;
- test the first (only) packet on that page to determine if it is a theora packet;
- once you have found a theora b_o_s page then use the retrieved serial_no to identify future packets belonging to the same theora stream.

Note that you cannot use theora_packet_isheader() to determine if a packet is a theora packet or not, as this function does not perform any checking beyond whether a header bit is present. Instead, use the theora_decode_header() function and check the return value; or examine the header bytes at the beginning of the Ogg page.