gavl

Data Structures | Macros | Enumerations | Functions
Compressed stream support

Compressed stream support. More...

## Data Structures
struct | gavl_compression_info_t
| Compression format. More...
struct | gavl_packet_t
| Packet structure. More...

## Macros
#define | GAVL_COMPRESSION_HAS_P_FRAMES (1<<0)
| Not all frames are keyframes.
#define | GAVL_COMPRESSION_HAS_B_FRAMES (1<<1)
| Frames don't appear in presentation order.
#define | GAVL_COMPRESSION_HAS_FIELD_PICTURES (1<<2)
| Packets can consist of 2 consecutive fields.
#define | GAVL_COMPRESSION_SBR (1<<3)
| Samplerate got doubled by decoder, format and sample counts are for the upsampled rate.
#define | GAVL_PACKET_TYPE_I 'I'
| Packet is an I-frame.
#define | GAVL_PACKET_TYPE_P 'P'
| Packet is a P-frame.
#define | GAVL_PACKET_TYPE_B 'B'
| Packet is a B-frame.
#define | GAVL_PACKET_TYPE_MASK 0xff
| Mask for frame type.
#define | GAVL_PACKET_KEYFRAME (1<<8)
| Packet is a keyframe.
#define | GAVL_PACKET_LAST (1<<9)
| Packet is the last in the stream (only Xiph codecs need this flag)

## Enumerations
enum | gavl_codec_id_t { GAVL_CODEC_ID_NONE = 0 , GAVL_CODEC_ID_ALAW = 1 , GAVL_CODEC_ID_ULAW , GAVL_CODEC_ID_MP2 , GAVL_CODEC_ID_MP3 , GAVL_CODEC_ID_AC3 , GAVL_CODEC_ID_AAC , GAVL_CODEC_ID_VORBIS , GAVL_CODEC_ID_FLAC , GAVL_CODEC_ID_JPEG = 0x10000 , GAVL_CODEC_ID_PNG , GAVL_CODEC_ID_TIFF , GAVL_CODEC_ID_TGA , GAVL_CODEC_ID_MPEG1 , GAVL_CODEC_ID_MPEG2 , GAVL_CODEC_ID_MPEG4_ASP , GAVL_CODEC_ID_H264 , GAVL_CODEC_ID_THEORA , GAVL_CODEC_ID_DIRAC , GAVL_CODEC_ID_DV }
| Codec ID. More...

## Functions
GAVL_PUBLIC void | gavl_compression_info_free (gavl_compression_info_t *info)
| Free all dynamically allocated memory of a compression info.
GAVL_PUBLIC void | gavl_compression_info_dump (const gavl_compression_info_t *info)
| Dump a compression info to stderr.
GAVL_PUBLIC void | gavl_compression_info_copy (gavl_compression_info_t *dst, const gavl_compression_info_t *src)
| Copy a compression info.
GAVL_PUBLIC const char * | gavl_compression_get_extension (gavl_codec_id_t id, int *separate)
| Get the file extension of the corresponding raw format.
GAVL_PUBLIC int | gavl_compression_need_pixelformat (gavl_codec_id_t id)
| Check if the compression supports multiple pixelformats.
GAVL_PUBLIC int | gavl_compression_constant_frame_samples (gavl_codec_id_t id)
| Check if an audio compression constant frame samples.
GAVL_PUBLIC void | gavl_packet_alloc (gavl_packet_t *p, int len)
| Allocate memory for a packet.
GAVL_PUBLIC void | gavl_packet_free (gavl_packet_t *p)
| Free memory of a packet.
GAVL_PUBLIC void | gavl_packet_dump (const gavl_packet_t *p)
| Dump a packet to stderr.

## Detailed Description

Compressed stream support.

gavl provides some structures and functions for handling compressed data packets. It is a completely independent API layer and has nothing to do with the uncompressed video and audio API. In particular the conversion between compressed and uncompressed data (i.e. codecs) are outside the scope of gavl. These are implemented in gmerlin-avdecoder and gmerlin encoding plugins.

## Macro Definition Documentation

## ◆ GAVL_COMPRESSION_HAS_P_FRAMES

#define GAVL_COMPRESSION_HAS_P_FRAMES (1<<0)

Not all frames are keyframes.

## ◆ GAVL_COMPRESSION_HAS_B_FRAMES

#define GAVL_COMPRESSION_HAS_B_FRAMES (1<<1)

Frames don't appear in presentation order.

## ◆ GAVL_COMPRESSION_HAS_FIELD_PICTURES

#define GAVL_COMPRESSION_HAS_FIELD_PICTURES (1<<2)

Packets can consist of 2 consecutive fields.

## ◆ GAVL_COMPRESSION_SBR

#define GAVL_COMPRESSION_SBR (1<<3)

Samplerate got doubled by decoder, format and sample counts are for the upsampled rate.

## ◆ GAVL_PACKET_TYPE_I

#define GAVL_PACKET_TYPE_I 'I'

Packet is an I-frame.

## ◆ GAVL_PACKET_TYPE_P

#define GAVL_PACKET_TYPE_P 'P'

Packet is a P-frame.

## ◆ GAVL_PACKET_TYPE_B

#define GAVL_PACKET_TYPE_B 'B'

Packet is a B-frame.

## ◆ GAVL_PACKET_TYPE_MASK

#define GAVL_PACKET_TYPE_MASK 0xff

Mask for frame type.

## ◆ GAVL_PACKET_KEYFRAME

#define GAVL_PACKET_KEYFRAME (1<<8)

Packet is a keyframe.

## ◆ GAVL_PACKET_LAST

#define GAVL_PACKET_LAST (1<<9)

Packet is the last in the stream (only Xiph codecs need this flag)

## Enumeration Type Documentation

## ◆ gavl_codec_id_t

enum gavl_codec_id_t

Codec ID.

These are used as identifiers for the type of compression

Enumerator
GAVL_CODEC_ID_NONE | Unknown/unsupported compression format.
GAVL_CODEC_ID_ALAW | alaw 2:1
GAVL_CODEC_ID_ULAW | mu-law 2:1
GAVL_CODEC_ID_MP2 | MPEG-1 audio layer II.
GAVL_CODEC_ID_MP3 | MPEG-1/2 audio layer 3 CBR/VBR.
GAVL_CODEC_ID_AC3 | AC3.
GAVL_CODEC_ID_AAC | AAC as stored in quicktime/mp4.
GAVL_CODEC_ID_VORBIS | Vorbis (segmented extradata and packets)
GAVL_CODEC_ID_FLAC | Flac (extradata contain a file header without comment and seektable)
GAVL_CODEC_ID_JPEG | JPEG image.
GAVL_CODEC_ID_PNG | PNG image.
GAVL_CODEC_ID_TIFF | TIFF image.
GAVL_CODEC_ID_TGA | TGA image.
GAVL_CODEC_ID_MPEG1 | MPEG-1 video.
GAVL_CODEC_ID_MPEG2 | MPEG-2 video.
GAVL_CODEC_ID_MPEG4_ASP | MPEG-4 ASP (a.k.a. Divx4)
GAVL_CODEC_ID_H264 | H.264 (Annex B)
GAVL_CODEC_ID_THEORA | Theora (segmented extradata)
GAVL_CODEC_ID_DIRAC | Complete DIRAC frames, sequence end code appended to last packet.
GAVL_CODEC_ID_DV | DV (several variants)

## Function Documentation

## ◆ gavl_compression_info_free()

GAVL_PUBLIC void gavl_compression_info_free | ( | gavl_compression_info_t * | info | ) |

Free all dynamically allocated memory of a compression info.

Parameters

  info | A compression info

## ◆ gavl_compression_info_dump()

GAVL_PUBLIC void gavl_compression_info_dump | ( | const gavl_compression_info_t * | info | ) |

Dump a compression info to stderr.

Parameters

  info | A compression info

Use this for debugging

## ◆ gavl_compression_info_copy()

GAVL_PUBLIC void gavl_compression_info_copy | ( | gavl_compression_info_t * | dst,
|  | const gavl_compression_info_t * | src
| ) |  |

Copy a compression info.

Parameters

  dst | Destination
  src | Source

## ◆ gavl_compression_get_extension()

GAVL_PUBLIC const char * gavl_compression_get_extension | ( | gavl_codec_id_t | id,
|  | int * | separate
| ) |  |

Get the file extension of the corresponding raw format.

Parameters

  id | A codec ID
  separate | If non-null returns 1 if each packet should be in a separate file

Returns
  The file extension of the raw file or NULL

This function can be used for writing elementary streams to files. It returns a suitable file extension. If separate is 1, each packet should be written to a separate file. This basically means, that the codec corresponds to an image format.

Not all compression formats have a suitable elementary stream format, in this case NULL is returned for the extension. Most prominent examples are Vorbis and Theora, which can hardly exist outside an OGG container.

## ◆ gavl_compression_need_pixelformat()

GAVL_PUBLIC int gavl_compression_need_pixelformat | ( | gavl_codec_id_t | id | ) |

Check if the compression supports multiple pixelformats.

Parameters

  id | A codec ID

Returns
  1 if the compression ID must be associated with a pixelformat, 0 else

This function can be used by decoding libraries to check if the compresison ID is sufficient or if the pixelformat must be valid in the associated video format.

## ◆ gavl_compression_constant_frame_samples()

GAVL_PUBLIC int gavl_compression_constant_frame_samples | ( | gavl_codec_id_t | id | ) |

Check if an audio compression constant frame samples.

Parameters

  id | A codec ID

Returns
  1 if the compression has the same number of samples in each frame, 0 else

## ◆ gavl_packet_alloc()

GAVL_PUBLIC void gavl_packet_alloc | ( | gavl_packet_t * | p,
|  | int | len
| ) |  |

Allocate memory for a packet.

Parameters

  p | A packet
  len | Number of bytes you want to store in the packet

This function uses realloc(), which means that it preserves the data already contained in the packet.

## ◆ gavl_packet_free()

GAVL_PUBLIC void gavl_packet_free | ( | gavl_packet_t * | p | ) |

Free memory of a packet.

Parameters

  p | A packet

## ◆ gavl_packet_dump()

GAVL_PUBLIC void gavl_packet_dump | ( | const gavl_packet_t * | p | ) |

Dump a packet to stderr.

Parameters

  p | A packet

Use this for debugging