flvdec.c

ffmpeg源码分析

/*
 * FLV encoder.
 * 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
 */
#include "avformat.h"

static int flv_probe(AVProbeData *p)
{
    const uint8_t *d;

    if (p->buf_size < 6)
        return 0;
    d = p->buf;
    if (d[0] == 'F' && d[1] == 'L' && d[2] == 'V') {
        return 50;
    }
    return 0;
}

static int flv_read_header(AVFormatContext *s,
                           AVFormatParameters *ap)
{
    int offset, flags, size;

    s->ctx_flags |= AVFMTCTX_NOHEADER; //ok we have a header but theres no fps, codec type, sample_rate, ...

    url_fskip(&s->pb, 4);
    flags = get_byte(&s->pb);

    offset = get_be32(&s->pb);

    if(!url_is_streamed(&s->pb)){
        const int fsize= url_fsize(&s->pb);
        url_fseek(&s->pb, fsize-4, SEEK_SET);
        size= get_be32(&s->pb);
        url_fseek(&s->pb, fsize-3-size, SEEK_SET);
        if(size == get_be24(&s->pb) + 11){
            s->duration= get_be24(&s->pb) * (int64_t)AV_TIME_BASE / 1000;
        }
    }

    url_fseek(&s->pb, offset, SEEK_SET);

    return 0;
}

static int flv_read_packet(AVFormatContext *s, AVPacket *pkt)
{
    int ret, i, type, size, pts, flags, is_audio, next;
    AVStream *st = NULL;

 for(;;){
    url_fskip(&s->pb, 4); /* size of previous packet */
    type = get_byte(&s->pb);
    size = get_be24(&s->pb);
    pts = get_be24(&s->pb);
//    av_log(s, AV_LOG_DEBUG, "type:%d, size:%d, pts:%d\n", type, size, pts);
    if (url_feof(&s->pb))
        return AVERROR_IO;
    url_fskip(&s->pb, 4); /* reserved */
    flags = 0;

    if(size == 0)
        continue;

    next= size + url_ftell(&s->pb);

    if (type == 8) {
        is_audio=1;
        flags = get_byte(&s->pb);
    } else if (type == 9) {
        is_audio=0;
        flags = get_byte(&s->pb);
    } else if (type == 18 && size > 13+1+4) {
        url_fskip(&s->pb, 13); //onMetaData blah
        if(get_byte(&s->pb) == 8){
            url_fskip(&s->pb, 4);
        }
        while(url_ftell(&s->pb) + 5 < next){
            char tmp[128];
            int type, len;
            double d= 0;

            len= get_be16(&s->pb);
            if(len >= sizeof(tmp) || !len)
                break;
            get_buffer(&s->pb, tmp, len);
            tmp[len]=0;

            type= get_byte(&s->pb);
            if(type==0){
                d= av_int2dbl(get_be64(&s->pb));
            }else if(type==2){
                len= get_be16(&s->pb);
                if(len >= sizeof(tmp))
                    break;
                url_fskip(&s->pb, len);
            }else if(type==8){
                //array
                break;
            }else if(type==11){
                d= av_int2dbl(get_be64(&s->pb));
                get_be16(&s->pb);
            }

            if(!strcmp(tmp, "duration")){
                s->duration = d*AV_TIME_BASE;
            }else if(!strcmp(tmp, "videodatarate")){
            }else if(!strcmp(tmp, "audiodatarate")){
            }
        }
        url_fseek(&s->pb, next, SEEK_SET);
        continue;
    } else {
        /* skip packet */
        av_log(s, AV_LOG_ERROR, "skipping flv packet: type %d, size %d, flags %d\n", type, size, flags);
        url_fseek(&s->pb, next, SEEK_SET);
        continue;
    }

    /* now find stream */
    for(i=0;i<s->nb_streams;i++) {
        st = s->streams[i];
        if (st->id == is_audio)
            break;
    }
    if(i == s->nb_streams){
        st = av_new_stream(s, is_audio);
        if (!st)
            return AVERROR_NOMEM;

        av_set_pts_info(st, 24, 1, 1000); /* 24 bit pts in ms */
        st->codec->time_base= (AVRational){1,1000};
    }
//    av_log(NULL, AV_LOG_DEBUG, "%d %X %d \n", is_audio, flags, st->discard);
    if(  (st->discard >= AVDISCARD_NONKEY && !((flags >> 4)==1 ||  is_audio))
       ||(st->discard >= AVDISCARD_BIDIR  &&  ((flags >> 4)==3 && !is_audio))
       || st->discard >= AVDISCARD_ALL
       ){
        url_fseek(&s->pb, next, SEEK_SET);
        continue;
    }
    break;
 }

    if(is_audio){
        if(st->codec->sample_rate == 0){
            st->codec->codec_type = CODEC_TYPE_AUDIO;
            st->codec->channels = (flags&1)+1;
            if((flags >> 4) == 5)
                st->codec->sample_rate= 8000;
            else
                st->codec->sample_rate = (44100<<((flags>>2)&3))>>3;
            switch(flags >> 4){/* 0: uncompressed 1: ADPCM 2: mp3 5: Nellymoser 8kHz mono 6: Nellymoser*/
            case 0: if (flags&2) st->codec->codec_id = CODEC_ID_PCM_S16BE;
                    else st->codec->codec_id = CODEC_ID_PCM_S8; break;
            case 1: st->codec->codec_id = CODEC_ID_ADPCM_SWF; break;
            case 2: st->codec->codec_id = CODEC_ID_MP3; break;
            // this is not listed at FLV but at SWF, strange...
            case 3: if (flags&2) st->codec->codec_id = CODEC_ID_PCM_S16LE;
                    else st->codec->codec_id = CODEC_ID_PCM_S8; break;
            default:
                    av_log(s, AV_LOG_INFO, "Unsupported audio codec (%x)\n", flags >> 4);
                st->codec->codec_tag= (flags >> 4);
            }
            st->codec->bits_per_sample = (flags & 2) ? 16 : 8;
        }
    }else{
            st->codec->codec_type = CODEC_TYPE_VIDEO;
            switch(flags & 0xF){
            case 2: st->codec->codec_id = CODEC_ID_FLV1; break;
            default:
                    av_log(s, AV_LOG_INFO, "Unsupported video codec (%x)\n", flags & 0xf);
                st->codec->codec_tag= flags & 0xF;
            }
    }

    ret= av_get_packet(&s->pb, pkt, size - 1);
    if (ret <= 0) {
        return AVERROR_IO;
    }
    /* note: we need to modify the packet size here to handle the last
       packet */
    pkt->size = ret;
    pkt->pts = pts;
    pkt->stream_index = st->index;

    if (is_audio || ((flags >> 4)==1))
        pkt->flags |= PKT_FLAG_KEY;

    return ret;
}

static int flv_read_close(AVFormatContext *s)
{
    return 0;
}

AVInputFormat flv_iformat = {
    "flv",
    "flv format",
    0,
    flv_probe,
    flv_read_header,
    flv_read_packet,
    flv_read_close,
    .extensions = "flv",
    .value = CODEC_ID_FLV1,
};

int flvdec_init(void)
{
    av_register_input_format(&flv_iformat);
    return 0;
}