vqavideo.c

ffmpeg源码分析

/*
 * Westwood Studios VQA Video Decoder
 * Copyright (C) 2003 the ffmpeg project
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 *
 */

/**
 * @file vqavideo.c
 * VQA Video Decoder by Mike Melanson ([e-mail])
 * 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.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "common.h"
#include "avcodec.h"
#include "dsputil.h"

#define PALETTE_COUNT 256
#define VQA_HEADER_SIZE 0x2A
#define CHUNK_PREAMBLE_SIZE 8

/* allocate the maximum vector space, regardless of the file version:
 * (0xFF00 codebook vectors + 0x100 solid pixel vectors) * (4x4 pixels/block) */
#define MAX_CODEBOOK_VECTORS 0xFF00
#define SOLID_PIXEL_VECTORS 0x100
#define MAX_VECTORS (MAX_CODEBOOK_VECTORS + SOLID_PIXEL_VECTORS)
#define MAX_CODEBOOK_SIZE (MAX_VECTORS * 4 * 4)

#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 VQA_DEBUG 0

#if VQA_DEBUG
#define vqa_debug printf
#else
static inline void vqa_debug(const char *format, ...) { }
#endif

typedef struct VqaContext {

    AVCodecContext *avctx;
    DSPContext dsp;
    AVFrame frame;

    unsigned char *buf;
    int size;

    unsigned int palette[PALETTE_COUNT];

    int width;   /* width of a frame */
    int height;   /* height of a frame */
    int vector_width;  /* width of individual vector */
    int vector_height;  /* height of individual vector */
    int vqa_version;  /* this should be either 1, 2 or 3 */

    unsigned char *codebook;         /* the current codebook */
    int codebook_size;
    unsigned char *next_codebook_buffer;  /* accumulator for next codebook */
    int next_codebook_buffer_index;

    unsigned char *decode_buffer;
    int decode_buffer_size;

    /* number of frames to go before replacing codebook */
    int partial_countdown;
    int partial_count;

} VqaContext;

static int vqa_decode_init(AVCodecContext *avctx)
{
    VqaContext *s = (VqaContext *)avctx->priv_data;
    unsigned char *vqa_header;
    int i, j, codebook_index;;

    s->avctx = avctx;
    avctx->pix_fmt = PIX_FMT_PAL8;
    avctx->has_b_frames = 0;
    dsputil_init(&s->dsp, avctx);

    /* make sure the extradata made it */
    if (s->avctx->extradata_size != VQA_HEADER_SIZE) {
        av_log(s->avctx, AV_LOG_ERROR, "  VQA video: expected extradata size of %d\n", VQA_HEADER_SIZE);
        return -1;
    }

    /* load up the VQA parameters from the header */
    vqa_header = (unsigned char *)s->avctx->extradata;
    s->vqa_version = vqa_header[0];
    s->width = LE_16(&vqa_header[6]);
    s->height = LE_16(&vqa_header[8]);
    if(avcodec_check_dimensions(avctx, s->width, s->height)){
        s->width= s->height= 0;
        return -1;
    }
    s->vector_width = vqa_header[10];
    s->vector_height = vqa_header[11];
    s->partial_count = s->partial_countdown = vqa_header[13];

    /* the vector dimensions have to meet very stringent requirements */
    if ((s->vector_width != 4) ||
        ((s->vector_height != 2) && (s->vector_height != 4))) {
        /* return without further initialization */
        return -1;
    }

    /* allocate codebooks */
    s->codebook_size = MAX_CODEBOOK_SIZE;
    s->codebook = av_malloc(s->codebook_size);
    s->next_codebook_buffer = av_malloc(s->codebook_size);

    /* initialize the solid-color vectors */
    if (s->vector_height == 4) {
        codebook_index = 0xFF00 * 16;
        for (i = 0; i < 256; i++)
            for (j = 0; j < 16; j++)
                s->codebook[codebook_index++] = i;
    } else {
        codebook_index = 0xF00 * 8;
        for (i = 0; i < 256; i++)
            for (j = 0; j < 8; j++)
                s->codebook[codebook_index++] = i;
    }
    s->next_codebook_buffer_index = 0;

    /* allocate decode buffer */
    s->decode_buffer_size = (s->width / s->vector_width) *
        (s->height / s->vector_height) * 2;
    s->decode_buffer = av_malloc(s->decode_buffer_size);

    s->frame.data[0] = NULL;

    return 0;
}

#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; \
    }

static void decode_format80(unsigned char *src, int src_size,
    unsigned char *dest, int dest_size, int check_size) {

    int src_index = 0;
    int dest_index = 0;
    int count;
    int src_pos;
    unsigned char color;
    int i;

    while (src_index < src_size) {

        vqa_debug("      opcode %02X: ", src[src_index]);

        /* 0x80 means that frame is finished */
        if (src[src_index] == 0x80)
            return;

        if (dest_index >= dest_size) {
            av_log(NULL, AV_LOG_ERROR, "  VQA video: decode_format80 problem: dest_index (%d) exceeded dest_size (%d)\n",
                dest_index, dest_size);
            return;
        }

        if (src[src_index] == 0xFF) {

            src_index++;
            count = LE_16(&src[src_index]);
            src_index += 2;
            src_pos = LE_16(&src[src_index]);
            src_index += 2;
            vqa_debug("(1) copy %X bytes from absolute pos %X\n", count, src_pos);
            CHECK_COUNT();
            for (i = 0; i < count; i++)
                dest[dest_index + i] = dest[src_pos + i];
            dest_index += count;

        } else if (src[src_index] == 0xFE) {

            src_index++;
            count = LE_16(&src[src_index]);
            src_index += 2;
            color = src[src_index++];
            vqa_debug("(2) set %X bytes to %02X\n", count, color);
            CHECK_COUNT();
            memset(&dest[dest_index], color, count);
            dest_index += count;

        } else if ((src[src_index] & 0xC0) == 0xC0) {

            count = (src[src_index++] & 0x3F) + 3;
            src_pos = LE_16(&src[src_index]);
            src_index += 2;
            vqa_debug("(3) copy %X bytes from absolute pos %X\n", count, src_pos);
            CHECK_COUNT();
            for (i = 0; i < count; i++)
                dest[dest_index + i] = dest[src_pos + i];
            dest_index += count;

        } else if (src[src_index] > 0x80) {

            count = src[src_index++] & 0x3F;
            vqa_debug("(4) copy %X bytes from source to dest\n", count);
            CHECK_COUNT();
            memcpy(&dest[dest_index], &src[src_index], count);
            src_index += count;
            dest_index += count;

        } else {

            count = ((src[src_index] & 0x70) >> 4) + 3;
            src_pos = BE_16(&src[src_index]) & 0x0FFF;
            src_index += 2;
            vqa_debug("(5) copy %X bytes from relpos %X\n", count, src_pos);
            CHECK_COUNT();
            for (i = 0; i < count; i++)
                dest[dest_index + i] = dest[dest_index - src_pos + i];
            dest_index += count;
        }
    }

    /* validate that the entire destination buffer was filled; this is
     * important for decoding frame maps since each vector needs to have a
     * codebook entry; it is not important for compressed codebooks because
     * not every entry needs to be filled */
    if (check_size)
        if (dest_index < dest_size)
            av_log(NULL, AV_LOG_ERROR, "  VQA video: decode_format80 problem: decode finished with dest_index (%d) < dest_size (%d)\n",
                dest_index, dest_size);
}

static void vqa_decode_chunk(VqaContext *s)
{
    unsigned int chunk_type;
    unsigned int chunk_size;
    int byte_skip;
    unsigned int index = 0;
    int i;
    unsigned char r, g, b;
    int index_shift;