# Functions for Encoding

You must link to `libtheoraenc` and `libtheoradec` if you use any of the functions in this section. The functions are listed in the order they are used in a typical encode. The basic steps are:

- Fill in a th_info structure with details on the format of the video you wish to encode.
- Allocate a th_enc_ctx handle with th_encode_alloc().
- Perform any additional encoder configuration required with th_encode_ctl().
- Repeatedly call th_encode_flushheader() to retrieve all the header packets.
- For each uncompressed frame:
  - Submit the uncompressed frame via th_encode_ycbcr_in()
  - Repeatedly call th_encode_packetout() to retrieve any video data packets that are ready.
- Call th_encode_free() to release all encoder memory.

th_enc_ctx * | th_encode_alloc (const th_info *_info)
| Allocates an encoder instance.
int | th_encode_ctl (th_enc_ctx *_enc, int _req, void *_buf, size_t _buf_sz)
| Encoder control function.
int | th_encode_flushheader (th_enc_ctx *_enc, th_comment *_comments, ogg_packet *_op)
| Outputs the next header packet.
int | th_encode_ycbcr_in (th_enc_ctx *_enc, th_ycbcr_buffer _ycbcr)
| Submits an uncompressed frame to the encoder.
int | th_encode_packetout (th_enc_ctx *_enc, int _last, ogg_packet *_op)
| Retrieves encoded video data packets.
void | th_encode_free (th_enc_ctx *_enc)
| Frees an allocated encoder instance.

## Function Documentation

th_enc_ctx* th_encode_alloc | ( | const th_info * | _info | ) |

Allocates an encoder instance.

Parameters:

  | _info | A th_info struct filled with the desired encoding parameters.

Returns:
  The initialized th_enc_ctx handle.

Return values:

  | NULL | If the encoding parameters were invalid.

int th_encode_ctl | ( | th_enc_ctx * | _enc,
|  | int | _req,
|  | void * | _buf,
|  | size_t | _buf_sz |
| ) |  |  |

Encoder control function.

This is used to provide advanced control the encoding process.

Parameters:

  | _enc | A th_enc_ctx handle.
  | _req | The control code to process. See the list of available control codes for details.
  | _buf | The parameters for this control code.
  | _buf_sz | The size of the parameter buffer.

int th_encode_flushheader | ( | th_enc_ctx * | _enc,
|  | th_comment * | _comments,
|  | ogg_packet * | _op |
| ) |  |  |

Outputs the next header packet.

This should be called repeatedly after encoder initialization until it returns 0 in order to get all of the header packets, in order, before encoding actual video data.

Parameters:

  | _enc | A th_enc_ctx handle.
  | _comments | The metadata to place in the comment header, when it is encoded.
  | _op | An `ogg_packet` structure to fill. All of the elements of this structure will be set, including a pointer to the header data. The memory for the header data is owned by `libtheoraenc`, and may be invalidated when the next encoder function is called.

Returns:
  A positive value indicates that a header packet was successfully produced.

Return values:

  | 0 | No packet was produced, and no more header packets remain.
  | TH_EFAULT | _enc, _comments, or _op was `NULL`.

void th_encode_free | ( | th_enc_ctx * | _enc | ) |

Frees an allocated encoder instance.

Parameters:

  | _enc | A th_enc_ctx handle.

int th_encode_packetout | ( | th_enc_ctx * | _enc,
|  | int | _last,
|  | ogg_packet * | _op |
| ) |  |  |

Retrieves encoded video data packets.

This should be called repeatedly after each frame is submitted to flush any encoded packets, until it returns 0. The encoder will not buffer these packets as subsequent frames are compressed, so a failure to do so will result in lost video data.

Note:
  Currently the encoder operates in a one-frame-in, one-packet-out manner. However, this may be changed in the future.

Parameters:

  | _enc | A th_enc_ctx handle.
  | _last | Set this flag to a non-zero value if no more uncompressed frames will be submitted. This ensures that a proper EOS flag is set on the last packet.
  | _op | An `ogg_packet` structure to fill. All of the elements of this structure will be set, including a pointer to the video data. The memory for the video data is owned by `libtheoraenc`, and may be invalidated when the next encoder function is called.

Returns:
  A positive value indicates that a video data packet was successfully produced.

Return values:

  | 0 | No packet was produced, and no more encoded video data remains.
  | TH_EFAULT | _enc or _op was `NULL`.

int th_encode_ycbcr_in | ( | th_enc_ctx * | _enc,
|  | th_ycbcr_buffer | _ycbcr |
| ) |  |  |

Submits an uncompressed frame to the encoder.

Parameters:

  | _enc | A th_enc_ctx handle.
  | _ycbcr | A buffer of Y'CbCr data to encode.

Return values:

  | 0 | Success.
  | TH_EFAULT | _enc or _ycbcr is `NULL`.
  | TH_EINVAL | The buffer size does not match the frame size the encoder was initialized with, or encoding has already completed.