libavcodec/vqavideo.c File Reference

VQA Video Decoder. More...

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "libavutil/intreadwrite.h"
#include "libavutil/imgutils.h"
#include "avcodec.h"

Go to the source code of this file.

Data Structures

struct  VqaContext


#define PALETTE_COUNT   256
#define VQA_HEADER_SIZE   0x2A
#define SOLID_PIXEL_VECTORS   0x100
#define CBF0_TAG   MKBETAG('C', 'B', 'F', '0')
#define CBFZ_TAG   MKBETAG('C', 'B', 'F', 'Z')
#define CBP0_TAG   MKBETAG('C', 'B', 'P', '0')
#define CBPZ_TAG   MKBETAG('C', 'B', 'P', 'Z')
#define CPL0_TAG   MKBETAG('C', 'P', 'L', '0')
#define CPLZ_TAG   MKBETAG('C', 'P', 'L', 'Z')
#define VPTZ_TAG   MKBETAG('V', 'P', 'T', 'Z')
#define CHECK_COUNT()


static av_cold int vqa_decode_init (AVCodecContext *avctx)
static void decode_format80 (const unsigned char *src, int src_size, unsigned char *dest, int dest_size, int check_size)
static void vqa_decode_chunk (VqaContext *s)
static int vqa_decode_frame (AVCodecContext *avctx, void *data, int *data_size, AVPacket *avpkt)
static av_cold int vqa_decode_end (AVCodecContext *avctx)


AVCodec ff_vqa_decoder

Detailed Description

VQA Video Decoder.

Mike Melanson (
See also:
The VQA video decoder outputs PAL8 or RGB555 colorspace data, depending on the type of data in the file.

This decoder needs the 42-byte VQHD header from the beginning of the VQA file passed through the extradata field. The VQHD header is laid out as:

bytes 0-3 chunk fourcc: 'VQHD' bytes 4-7 chunk size in big-endian format, should be 0x0000002A bytes 8-49 VQHD chunk data

Bytes 8-49 are what this decoder expects to see.

Briefly, VQA is a vector quantized animation format that operates in a VGA palettized colorspace. It operates on pixel vectors (blocks) of either 4x2 or 4x4 in size. Compressed VQA chunks can contain vector codebooks, palette information, and code maps for rendering vectors onto frames. Any of these components can also be compressed with a run-length encoding (RLE) algorithm commonly referred to as "format80".

VQA takes a novel approach to rate control. Each group of n frames (usually, n = 8) relies on a different vector codebook. Rather than transporting an entire codebook every 8th frame, the new codebook is broken up into 8 pieces and sent along with the compressed video chunks for each of the 8 frames preceding the 8 frames which require the codebook. A full codebook is also sent on the very first frame of a file. This is an interesting technique, although it makes random file seeking difficult despite the fact that the frames are all intracoded.

V1,2 VQA uses 12-bit codebook indexes. If the 12-bit indexes were packed into bytes and then RLE compressed, bytewise, the results would be poor. That is why the coding method divides each index into 2 parts, the top 4 bits and the bottom 8 bits, then RL encodes the 4-bit pieces together and the 8-bit pieces together. If most of the vectors are clustered into one group of 256 vectors, most of the 4-bit index pieces should be the same.

Definition in file vqavideo.c.

Define Documentation

#define CBF0_TAG   MKBETAG('C', 'B', 'F', '0')

Definition at line 85 of file vqavideo.c.

Referenced by vqa_decode_chunk().

#define CBFZ_TAG   MKBETAG('C', 'B', 'F', 'Z')

Definition at line 86 of file vqavideo.c.

Referenced by vqa_decode_chunk().

#define CBP0_TAG   MKBETAG('C', 'B', 'P', '0')

Definition at line 87 of file vqavideo.c.

Referenced by vqa_decode_chunk().

#define CBPZ_TAG   MKBETAG('C', 'B', 'P', 'Z')

Definition at line 88 of file vqavideo.c.

Referenced by vqa_decode_chunk().

#define CHECK_COUNT (  ) 


if (dest_index + count > dest_size) { \
        av_log(NULL, AV_LOG_ERROR, "  VQA video: decode_format80 problem: next op would overflow dest_index\n"); \
        av_log(NULL, AV_LOG_ERROR, "  VQA video: current dest_index = %d, count = %d, dest_size = %d\n", \
            dest_index, count, dest_size); \
        return; \

Definition at line 197 of file vqavideo.c.

Referenced by decode_format80(), and mpegts_probe().


Definition at line 76 of file vqavideo.c.

Referenced by ipmovie_read_header(), process_ipmovie_chunk(), and vqa_decode_chunk().

#define CPL0_TAG   MKBETAG('C', 'P', 'L', '0')

Definition at line 89 of file vqavideo.c.

Referenced by vqa_decode_chunk().

#define CPLZ_TAG   MKBETAG('C', 'P', 'L', 'Z')

Definition at line 90 of file vqavideo.c.

Referenced by vqa_decode_chunk().


Definition at line 83 of file vqavideo.c.

Referenced by vqa_decode_chunk(), and vqa_decode_init().


Definition at line 80 of file vqavideo.c.


Definition at line 82 of file vqavideo.c.

#define PALETTE_COUNT   256

Definition at line 74 of file vqavideo.c.

#define SOLID_PIXEL_VECTORS   0x100

Definition at line 81 of file vqavideo.c.

#define VPTZ_TAG   MKBETAG('V', 'P', 'T', 'Z')

Definition at line 91 of file vqavideo.c.

Referenced by vqa_decode_chunk().

#define VQA_HEADER_SIZE   0x2A

Definition at line 75 of file vqavideo.c.

Referenced by vqa_decode_init(), and wsvqa_read_header().

Function Documentation

static void decode_format80 ( const unsigned char *  src,
int  src_size,
unsigned char *  dest,
int  dest_size,
int  check_size 
) [static]

Definition at line 205 of file vqavideo.c.

Referenced by vqa_decode_chunk().

static void vqa_decode_chunk ( VqaContext s  )  [static]

Definition at line 302 of file vqavideo.c.

Referenced by vqa_decode_frame().

static av_cold int vqa_decode_end ( AVCodecContext avctx  )  [static]

Definition at line 605 of file vqavideo.c.

static int vqa_decode_frame ( AVCodecContext avctx,
void *  data,
int *  data_size,
AVPacket avpkt 
) [static]

Definition at line 573 of file vqavideo.c.

static av_cold int vqa_decode_init ( AVCodecContext avctx  )  [static]

Definition at line 123 of file vqavideo.c.

Variable Documentation

Initial value:

    .name           = "vqavideo",
    .type           = AVMEDIA_TYPE_VIDEO,
    .id             = CODEC_ID_WS_VQA,
    .priv_data_size = sizeof(VqaContext),
    .init           = vqa_decode_init,
    .close          = vqa_decode_end,
    .decode         = vqa_decode_frame,
    .capabilities   = CODEC_CAP_DR1,
    .long_name = NULL_IF_CONFIG_SMALL("Westwood Studios VQA (Vector Quantized Animation) video"),

Definition at line 619 of file vqavideo.c.

Generated on Fri Oct 26 02:43:50 2012 for FFmpeg by  doxygen 1.5.8