avidec.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

    for(i=sync=url_ftell(pb); !url_feof(pb); i++) {
        int j;

        for(j=0; j<7; j++)
            d[j]= d[j+1];
        d[7]= get_byte(pb);

        size= d[4] + (d[5]<<8) + (d[6]<<16) + (d[7]<<24);

        if(    d[2] >= '0' && d[2] <= '9'
            && d[3] >= '0' && d[3] <= '9'){
            n= (d[2] - '0') * 10 + (d[3] - '0');
        }else{
            n= 100; //invalid stream id
        }
//av_log(NULL, AV_LOG_DEBUG, "%X %X %X %X %X %X %X %X %"PRId64" %d %d\n", d[0], d[1], d[2], d[3], d[4], d[5], d[6], d[7], i, size, n);
        if(i + size > avi->fsize || d[0]<0)
            continue;

        //parse ix##
        if(  (d[0] == 'i' && d[1] == 'x' && n < s->nb_streams)
        //parse JUNK
           ||(d[0] == 'J' && d[1] == 'U' && d[2] == 'N' && d[3] == 'K')
           ||(d[0] == 'i' && d[1] == 'd' && d[2] == 'x' && d[3] == '1')){
            url_fskip(pb, size);
//av_log(NULL, AV_LOG_DEBUG, "SKIP\n");
            goto resync;
        }

        if(    d[0] >= '0' && d[0] <= '9'
            && d[1] >= '0' && d[1] <= '9'){
            n= (d[0] - '0') * 10 + (d[1] - '0');
        }else{
            n= 100; //invalid stream id
        }

        //parse ##dc/##wb
        if(n < s->nb_streams){
          AVStream *st;
          AVIStream *ast;
          st = s->streams[n];
          ast = st->priv_data;

          if(   (st->discard >= AVDISCARD_DEFAULT && size==0)
             /*|| (st->discard >= AVDISCARD_NONKEY && !(pkt->flags & PKT_FLAG_KEY))*/ //FIXME needs a little reordering
             || st->discard >= AVDISCARD_ALL){
                if(ast->sample_size) ast->frame_offset += pkt->size;
                else                 ast->frame_offset++;
                url_fskip(pb, size);
                goto resync;
          }

          if(   ((ast->prefix_count<5 || sync+9 > i) && d[2]<128 && d[3]<128) ||
                d[2]*256+d[3] == ast->prefix /*||
                (d[2] == 'd' && d[3] == 'c') ||
                (d[2] == 'w' && d[3] == 'b')*/) {

//av_log(NULL, AV_LOG_DEBUG, "OK\n");
            if(d[2]*256+d[3] == ast->prefix)
                ast->prefix_count++;
            else{
                ast->prefix= d[2]*256+d[3];
                ast->prefix_count= 0;
            }

            avi->stream_index= n;
            ast->packet_size= size + 8;
            ast->remaining= size;

            {
                uint64_t pos= url_ftell(pb) - 8;
                if(!st->index_entries || !st->nb_index_entries || st->index_entries[st->nb_index_entries - 1].pos < pos){
                    av_add_index_entry(st, pos, ast->frame_offset / FFMAX(1, ast->sample_size), size, 0, AVINDEX_KEYFRAME);
                }
            }
            goto resync;
          }
        }
        /* palette changed chunk */
        if (   d[0] >= '0' && d[0] <= '9'
            && d[1] >= '0' && d[1] <= '9'
            && ((d[2] == 'p' && d[3] == 'c'))
            && n < s->nb_streams && i + size <= avi->fsize) {

            AVStream *st;
            int first, clr, flags, k, p;

            st = s->streams[n];

            first = get_byte(pb);
            clr = get_byte(pb);
            if(!clr) /* all 256 colors used */
                clr = 256;
            flags = get_le16(pb);
            p = 4;
            for (k = first; k < clr + first; k++) {
                int r, g, b;
                r = get_byte(pb);
                g = get_byte(pb);
                b = get_byte(pb);
                    get_byte(pb);
                st->codec->palctrl->palette[k] = b + (g << 8) + (r << 16);
            }
            st->codec->palctrl->palette_changed = 1;
            goto resync;
        }

    }

    return -1;
}

/* XXX: we make the implicit supposition that the position are sorted
   for each stream */
static int avi_read_idx1(AVFormatContext *s, int size)
{
    AVIContext *avi = s->priv_data;
    ByteIOContext *pb = &s->pb;
    int nb_index_entries, i;
    AVStream *st;
    AVIStream *ast;
    unsigned int index, tag, flags, pos, len;
    unsigned last_pos= -1;

    nb_index_entries = size / 16;
    if (nb_index_entries <= 0)
        return -1;

    /* read the entries and sort them in each stream component */
    for(i = 0; i < nb_index_entries; i++) {
        tag = get_le32(pb);
        flags = get_le32(pb);
        pos = get_le32(pb);
        len = get_le32(pb);
#if defined(DEBUG_SEEK)
        av_log(NULL, AV_LOG_DEBUG, "%d: tag=0x%x flags=0x%x pos=0x%x len=%d/",
               i, tag, flags, pos, len);
#endif
        if(i==0 && pos > avi->movi_list)
            avi->movi_list= 0; //FIXME better check
        pos += avi->movi_list;

        index = ((tag & 0xff) - '0') * 10;
        index += ((tag >> 8) & 0xff) - '0';
        if (index >= s->nb_streams)
            continue;
        st = s->streams[index];
        ast = st->priv_data;

#if defined(DEBUG_SEEK)
        av_log(NULL, AV_LOG_DEBUG, "%d cum_len=%"PRId64"\n", len, ast->cum_len);
#endif
        if(last_pos == pos)
            avi->non_interleaved= 1;
        else
            av_add_index_entry(st, pos, ast->cum_len / FFMAX(1, ast->sample_size), len, 0, (flags&AVIIF_INDEX) ? AVINDEX_KEYFRAME : 0);
        if(ast->sample_size)
            ast->cum_len += len;
        else
            ast->cum_len ++;
        last_pos= pos;
    }
    return 0;
}

static int guess_ni_flag(AVFormatContext *s){
    int i;
    int64_t last_start=0;
    int64_t first_end= INT64_MAX;

    for(i=0; i<s->nb_streams; i++){
        AVStream *st = s->streams[i];
        int n= st->nb_index_entries;

        if(n <= 0)
            continue;

        if(st->index_entries[0].pos > last_start)
            last_start= st->index_entries[0].pos;
        if(st->index_entries[n-1].pos < first_end)
            first_end= st->index_entries[n-1].pos;
    }
    return last_start > first_end;
}

static int avi_load_index(AVFormatContext *s)
{
    AVIContext *avi = s->priv_data;
    ByteIOContext *pb = &s->pb;
    uint32_t tag, size;
    offset_t pos= url_ftell(pb);

    url_fseek(pb, avi->movi_end, SEEK_SET);
#ifdef DEBUG_SEEK
    printf("movi_end=0x%"PRIx64"\n", avi->movi_end);
#endif
    for(;;) {
        if (url_feof(pb))
            break;
        tag = get_le32(pb);
        size = get_le32(pb);
#ifdef DEBUG_SEEK
        printf("tag=%c%c%c%c size=0x%x\n",
               tag & 0xff,
               (tag >> 8) & 0xff,
               (tag >> 16) & 0xff,
               (tag >> 24) & 0xff,
               size);
#endif
        switch(tag) {
        case MKTAG('i', 'd', 'x', '1'):
            if (avi_read_idx1(s, size) < 0)
                goto skip;
            else
                goto the_end;
            break;
        default:
        skip:
            size += (size & 1);
            url_fskip(pb, size);
            break;
        }
    }
 the_end:
    url_fseek(pb, pos, SEEK_SET);
    return 0;
}

static int avi_read_seek(AVFormatContext *s, int stream_index, int64_t timestamp, int flags)
{
    AVIContext *avi = s->priv_data;
    AVStream *st;
    int i, index;
    int64_t pos;

    if (!avi->index_loaded) {
        /* we only load the index on demand */
        avi_load_index(s);
        avi->index_loaded = 1;
    }
    assert(stream_index>= 0);

    st = s->streams[stream_index];
    index= av_index_search_timestamp(st, timestamp, flags);
    if(index<0)
        return -1;

    /* find the position */
    pos = st->index_entries[index].pos;
    timestamp = st->index_entries[index].timestamp;

//    av_log(NULL, AV_LOG_DEBUG, "XX %"PRId64" %d %"PRId64"\n", timestamp, index, st->index_entries[index].timestamp);

    if (ENABLE_DV_DEMUXER && avi->dv_demux) {
        /* One and only one real stream for DV in AVI, and it has video  */
        /* offsets. Calling with other stream indices should have failed */
        /* the av_index_search_timestamp call above.                     */
        assert(stream_index == 0);

        /* Feed the DV video stream version of the timestamp to the */
        /* DV demux so it can synth correct timestamps              */
        dv_offset_reset(avi->dv_demux, timestamp);

        url_fseek(&s->pb, pos, SEEK_SET);
        avi->stream_index= -1;
        return 0;
    }

    for(i = 0; i < s->nb_streams; i++) {
        AVStream *st2 = s->streams[i];
        AVIStream *ast2 = st2->priv_data;

        ast2->packet_size=
        ast2->remaining= 0;

        if (st2->nb_index_entries <= 0)
            continue;

//        assert(st2->codec->block_align);
        assert(st2->time_base.den == ast2->rate);
        assert(st2->time_base.num == ast2->scale);
        index = av_index_search_timestamp(
                st2,
                av_rescale(timestamp, st2->time_base.den*(int64_t)st->time_base.num, st->time_base.den * (int64_t)st2->time_base.num),
                flags | AVSEEK_FLAG_BACKWARD);
        if(index<0)
            index=0;

        if(!avi->non_interleaved){
            while(index>0 && st2->index_entries[index].pos > pos)
                index--;
            while(index+1 < st2->nb_index_entries && st2->index_entries[index].pos < pos)
                index++;
        }

//        av_log(NULL, AV_LOG_DEBUG, "%"PRId64" %d %"PRId64"\n", timestamp, index, st2->index_entries[index].timestamp);
        /* extract the current frame number */
        ast2->frame_offset = st2->index_entries[index].timestamp;
        if(ast2->sample_size)
            ast2->frame_offset *=ast2->sample_size;
    }

    /* do the seek */
    url_fseek(&s->pb, pos, SEEK_SET);
    avi->stream_index= -1;
    return 0;
}

static int avi_read_close(AVFormatContext *s)
{
    int i;
    AVIContext *avi = s->priv_data;

    for(i=0;i<s->nb_streams;i++) {
        AVStream *st = s->streams[i];
        AVIStream *ast = st->priv_data;
        av_free(ast);
        av_free(st->codec->palctrl);
    }

    if (avi->dv_demux)
        av_free(avi->dv_demux);

    return 0;
}

static int avi_probe(AVProbeData *p)
{
    int i;

    /* check file header */
    for(i=0; avi_headers[i][0]; i++)
        if(!memcmp(p->buf  , avi_headers[i]  , 4) &&
           !memcmp(p->buf+8, avi_headers[i]+4, 4))
            return AVPROBE_SCORE_MAX;

    return 0;
}

AVInputFormat avi_demuxer = {
    "avi",
    "avi format",
    sizeof(AVIContext),
    avi_probe,
    avi_read_header,
    avi_read_packet,
    avi_read_close,
    avi_read_seek,
};