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# theoradec.h File Reference

The `libtheoradec` C decoding API. More...

`#include <ogg/ogg.h>`
`#include "codec.h"`

Go to the source code of this file.

## Data Structures
struct | th_stripe_callback
| The striped decode callback data to pass to TH_DECCTL_SET_STRIPE_CB. More...
## Defines
#define | _O_THEORA_THEORADEC_H_ (1)
th_decode_ctl() codes
These are the available request codes for th_decode_ctl(). By convention, these are odd, to distinguish them from the encoder control codes. Keep any experimental or vendor-specific values above `0x8000`.
#define | TH_DECCTL_GET_PPLEVEL_MAX (1)
| Gets the maximum post-processing level.
#define | TH_DECCTL_SET_PPLEVEL (3)
| Sets the post-processing level.
#define | TH_DECCTL_SET_GRANPOS (5)
| Sets the granule position.
#define | TH_DECCTL_SET_STRIPE_CB (7)
| Sets the striped decode callback function.
## Typedefs
typedef void(*) | th_stripe_decoded_func (void *_ctx, th_ycbcr_buffer _buf, int _yfrag0, int _yfrag_end)
| A callback function for striped decode.
Decoder state
The following data structures are opaque, and their contents are not publicly defined by this API. Referring to their internals directly is unsupported, and may break without warning.
typedef th_dec_ctx | th_dec_ctx
| The decoder context.
typedef th_setup_info | th_setup_info
| Setup information.
## Functions
Functions for decoding
You must link to `libtheoradec` if you use any of the functions in this section. The functions are listed in the order they are used in a typical decode. The basic steps are: Parse the header packets by repeatedly calling th_decode_headerin(). Allocate a th_dec_ctx handle with th_decode_alloc(). Call th_setup_free() to free any memory used for codec setup information. Perform any additional decoder configuration with th_decode_ctl(). For each video data packet: Submit the packet to the decoder via th_decode_packetin(). Retrieve the uncompressed video data via th_decode_ycbcr_out(). Call th_decode_free() to release all decoder memory.
int | th_decode_headerin (th_info *_info, th_comment *_tc, th_setup_info **_setup, ogg_packet *_op)
| Decodes the header packets of a Theora stream.
th_dec_ctx * | th_decode_alloc (const th_info *_info, const th_setup_info *_setup)
| Allocates a decoder instance.
void | th_setup_free (th_setup_info *_setup)
| Releases all storage used for the decoder setup information.
int | th_decode_ctl (th_dec_ctx *_dec, int _req, void *_buf, size_t _buf_sz)
| Decoder control function.
int | th_decode_packetin (th_dec_ctx *_dec, const ogg_packet *_op, ogg_int64_t *_granpos)
| Submits a packet containing encoded video data to the decoder.
int | th_decode_ycbcr_out (th_dec_ctx *_dec, th_ycbcr_buffer _ycbcr)
| Outputs the next available frame of decoded Y'CbCr data.
void | th_decode_free (th_dec_ctx *_dec)
| Frees an allocated decoder instance.

## Detailed Description

The `libtheoradec` C decoding API.

## Define Documentation

#define TH_DECCTL_GET_PPLEVEL_MAX (1)

Gets the maximum post-processing level.

Parameters:

  `[out]` | _buf | int: The maximum post-processing level.

Return values:

  | TH_EFAULT | _dec_ctx or _buf is `NULL`.
  | TH_EINVAL | _buf_sz is not `sizeof(int)`.
  | TH_EIMPL | Not supported by this implementation.

#define TH_DECCTL_SET_GRANPOS (5)

Sets the granule position.

Call this after a seek, before decoding the first frame, to ensure that the proper granule position is returned for all subsequent frames. If you track timestamps yourself and do not use the granule position returned by the decoder, then you need not call this function.

Parameters:

  `[in]` | _buf | `ogg_int64_t`: The granule position of the next frame.

Return values:

  | TH_EFAULT | _dec_ctx or _buf is `NULL`.
  | TH_EINVAL | _buf_sz is not `sizeof(ogg_int64_t)`, or the granule position is negative.

#define TH_DECCTL_SET_PPLEVEL (3)

Sets the post-processing level.

By default, post-processing is disabled.

Parameters:

  `[in]` | _buf | int: The new post-processing level. 0 to disable; larger values use more CPU.

Return values:

  | TH_EFAULT | _dec_ctx or _buf is `NULL`.
  | TH_EINVAL | _buf_sz is not `sizeof(int)`, or the post-processing level is out of bounds. The maximum post-processing level may be implementation-specific, and can be obtained via TH_DECCTL_GET_PPLEVEL_MAX.
  | TH_EIMPL | Not supported by this implementation.

#define TH_DECCTL_SET_STRIPE_CB (7)

Sets the striped decode callback function.

If set, this function will be called as each piece of a frame is fully decoded in th_decode_packetin(). You can pass in a th_stripe_callback with th_stripe_callback::stripe_decoded set to `NULL` to disable the callbacks at any point. Enabling striped decode does not prevent you from calling th_decode_ycbcr_out() after the frame is fully decoded.

Parameters:

  `[in]` | _buf | th_stripe_callback: The callback parameters.

Return values:

  | TH_EFAULT | _dec_ctx or _buf is `NULL`.
  | TH_EINVAL | _buf_sz is not `sizeof(th_stripe_callback)`.

## Typedef Documentation

typedef struct th_setup_info th_setup_info

Setup information.

This contains auxiliary information (Huffman tables and quantization parameters) decoded from the setup header by th_decode_headerin() to be passed to th_decode_alloc(). It can be re-used to initialize any number of decoders, and can be freed via th_setup_free() at any time.

typedef void(*) th_stripe_decoded_func(void *_ctx, th_ycbcr_buffer _buf, int _yfrag0, int _yfrag_end)

A callback function for striped decode.

This is a function pointer to an application-provided function that will be called each time a section of the image is fully decoded in th_decode_packetin(). This allows the application to process the section immediately, while it is still in cache. Note that the frame is decoded bottom to top, so _yfrag0 will steadily decrease with each call until it reaches 0, at which point the full frame is decoded. The number of fragment rows made available in each call depends on the pixel format and the number of post-processing filters enabled, and may not even be constant for the entire frame. If a non-`NULL` _granpos pointer is passed to th_decode_packetin(), the granule position for the frame will be stored in it before the first callback is made. If an entire frame is dropped (a 0-byte packet), then no callbacks will be made at all for that frame.

Parameters:

  | _ctx | An application-provided context pointer.
  | _buf | The image buffer for the decoded frame.
  | _yfrag0 | The Y coordinate of the first row of 8x8 fragments decoded. Multiply this by 8 to obtain the pixel row number in the luma plane. If the chroma planes are subsampled in the Y direction, this will always be divisible by two.
  | _yfrag_end | The Y coordinate of the first row of 8x8 fragments past the newly decoded section. If the chroma planes are subsampled in the Y direction, this will always be divisible by two. I.e., this section contains fragment rows `_yfrag0 ..._yfrag_end -1`.