h261_parser.c

mediastreamer2是开源的网络传输媒体流的库

/*
 * H261 parser
 * Copyright (c) 2002-2004 Michael Niedermayer <[e-mail]>
 * Copyright (c) 2004 Maarten Daniels
 *
 * 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
 */

/**
 * @file h261_parser.c
 * h261codec.
 */

#include "parser.h"


static int h261_find_frame_end(ParseContext *pc, AVCodecContext* avctx, const uint8_t *buf, int buf_size){
    int vop_found, i, j;
    uint32_t state;

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

    for(i=0; i<buf_size && !vop_found; i++){
        state= (state<<8) | buf[i];
        for(j=0; j<8; j++){
            if(((state>>j)&0xFFFFF0) == 0x000100){
                vop_found=1;
                break;
            }
        }
    }
    if(vop_found){
        for(; i<buf_size; i++){
            state= (state<<8) | buf[i];
            for(j=0; j<8; j++){
                if(((state>>j)&0xFFFFF0) == 0x000100){
                    pc->frame_start_found=0;
                    pc->state= (state>>(3*8))+0xFF00;
                    return i-2;
                }
            }
        }
    }

    pc->frame_start_found= vop_found;
    pc->state= state;
    return END_NOT_FOUND;
}

static int h261_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;

    next= h261_find_frame_end(pc,avctx, buf, buf_size);
    if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
        *poutbuf = NULL;
        *poutbuf_size = 0;
        return buf_size;
    }
    *poutbuf = buf;
    *poutbuf_size = buf_size;
    return next;
}

AVCodecParser h261_parser = {
    { CODEC_ID_H261 },
    sizeof(ParseContext),
    NULL,
    h261_parse,
    ff_parse_close,
};