FFmpeg/libavcodec/mpeg4video_parser.c

/*
 * MPEG4 Video frame extraction
 * Copyright (c) 2003 Fabrice Bellard
 * Copyright (c) 2003 Michael Niedermayer
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg 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 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg 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 FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#define UNCHECKED_BITSTREAM_READER 1

#include "parser.h"
#include "mpegvideo.h"
#include "mpeg4video.h"
#include "mpeg4video_parser.h"

struct Mp4vParseContext {
    ParseContext pc;
    struct MpegEncContext enc;
    int first_picture;
};

int ff_mpeg4_find_frame_end(ParseContext *pc, const uint8_t *buf, int buf_size){
    int vop_found, i;
    uint32_t state;

    vop_found= pc->frame_start_found;
    state= pc->state;

    i=0;
    if(!vop_found){
        for(i=0; i<buf_size; i++){
            state= (state<<8) | buf[i];
            if(state == 0x1B6){
                i++;
                vop_found=1;
                break;
            }
        }
    }

    if(vop_found){
        /* EOF considered as end of frame */
        if (buf_size == 0)
            return 0;
        for(; i<buf_size; i++){
            state= (state<<8) | buf[i];
            if((state&0xFFFFFF00) == 0x100){
                pc->frame_start_found=0;
                pc->state=-1;
                return i-3;
            }
        }
    }
    pc->frame_start_found= vop_found;
    pc->state= state;
    return END_NOT_FOUND;
}

/* XXX: make it use less memory */
static int av_mpeg4_decode_header(AVCodecParserContext *s1,
                                  AVCodecContext *avctx,
                                  const uint8_t *buf, int buf_size)
{
    struct Mp4vParseContext *pc = s1->priv_data;
    MpegEncContext *s = &pc->enc;
    GetBitContext gb1, *gb = &gb1;
    int ret;

    s->avctx = avctx;
    s->current_picture_ptr = &s->current_picture;

    if (avctx->extradata_size && pc->first_picture){
        init_get_bits(gb, avctx->extradata, avctx->extradata_size*8);
        ret = ff_mpeg4_decode_picture_header(s, gb);
    }

    init_get_bits(gb, buf, 8 * buf_size);
    ret = ff_mpeg4_decode_picture_header(s, gb);
    if (s->width && (!avctx->width || !avctx->height || !avctx->coded_width || !avctx->coded_height)) {
        avcodec_set_dimensions(avctx, s->width, s->height);
    }
    s1->pict_type= s->pict_type;
    pc->first_picture = 0;
    return ret;
}

static av_cold int mpeg4video_parse_init(AVCodecParserContext *s)
{
    struct Mp4vParseContext *pc = s->priv_data;

    pc->first_picture = 1;
    pc->enc.quant_precision=5;
    pc->enc.slice_context_count = 1;
    return 0;
}

static int mpeg4video_parse(AVCodecParserContext *s,
                           AVCodecContext *avctx,
                           const uint8_t **poutbuf, int *poutbuf_size,
                           const uint8_t *buf, int buf_size)
{
    ParseContext *pc = s->priv_data;
    int next;

    if(s->flags & PARSER_FLAG_COMPLETE_FRAMES){
        next= buf_size;
    }else{
        next= ff_mpeg4_find_frame_end(pc, buf, buf_size);

        if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
            *poutbuf = NULL;
            *poutbuf_size = 0;
            return buf_size;
        }
    }
    av_mpeg4_decode_header(s, avctx, buf, buf_size);

    *poutbuf = buf;
    *poutbuf_size = buf_size;
    return next;
}


AVCodecParser ff_mpeg4video_parser = {
    .codec_ids      = { CODEC_ID_MPEG4 },
    .priv_data_size = sizeof(struct Mp4vParseContext),
    .parser_init    = mpeg4video_parse_init,
    .parser_parse   = mpeg4video_parse,
    .parser_close   = ff_parse_close,
    .split          = ff_mpeg4video_split,
};