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vqavideo.c File Reference


Detailed Description

VQA Video Decoder by Mike Melanson (melanson@pcisys.net) For more information about the RPZA format, visit: http://www.pcisys.net/~melanson/codecs/

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 indices. If the 12-bit indices 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.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "common.h"
#include "avcodec.h"
#include "dsputil.h"

Go to the source code of this file.

Classes

struct  VqaContext

Defines

#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 CHECK_COUNT()
#define CHUNK_PREAMBLE_SIZE   8
#define CPL0_TAG   MKBETAG('C', 'P', 'L', '0')
#define CPLZ_TAG   MKBETAG('C', 'P', 'L', 'Z')
#define MAX_CODEBOOK_SIZE   (MAX_VECTORS * 4 * 4)
#define MAX_CODEBOOK_VECTORS   0xFF00
#define MAX_VECTORS   (MAX_CODEBOOK_VECTORS + SOLID_PIXEL_VECTORS)
#define PALETTE_COUNT   256
#define SOLID_PIXEL_VECTORS   0x100
#define VPTZ_TAG   MKBETAG('V', 'P', 'T', 'Z')
#define VQA_DEBUG   0
#define VQA_HEADER_SIZE   0x2A

Functions

static void decode_format80 (unsigned char *src, int src_size, unsigned char *dest, int dest_size, int check_size)
static void vqa_debug (const char *format,...)
static void vqa_decode_chunk (VqaContext *s)
static int vqa_decode_end (AVCodecContext *avctx)
static int vqa_decode_frame (AVCodecContext *avctx, void *data, int *data_size, uint8_t *buf, int buf_size)
static int vqa_decode_init (AVCodecContext *avctx)

Variables

AVCodec vqa_decoder


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