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

                ast->rate = get_le32(pb);
                url_fskip(pb, 4);  /* start time */

                dv_dur = get_le32(pb);
                if (ast->scale > 0 && ast->rate > 0 && dv_dur > 0) {
                    dv_dur *= AV_TIME_BASE;
                    s->duration = av_rescale(dv_dur, ast->scale, ast->rate);
                }
                /*
                 * else, leave duration alone; timing estimation in utils.c
                 *      will make a guess based on bit rate.
                 */

                stream_index = s->nb_streams - 1;
                url_fskip(pb, size - 9*4);
                break;
            }

            assert(stream_index < s->nb_streams);
            st->codec->stream_codec_tag= handler;

            get_le32(pb); /* flags */
            get_le16(pb); /* priority */
            get_le16(pb); /* language */
            get_le32(pb); /* initial frame */
            ast->scale = get_le32(pb);
            ast->rate = get_le32(pb);
            if(ast->scale && ast->rate){
            }else if(frame_period){
                ast->rate = 1000000;
                ast->scale = frame_period;
            }else{
                ast->rate = 25;
                ast->scale = 1;
            }
            av_set_pts_info(st, 64, ast->scale, ast->rate);

            ast->cum_len=get_le32(pb); /* start */
            nb_frames = get_le32(pb);

            st->start_time = 0;
            st->duration = nb_frames;
            get_le32(pb); /* buffer size */
            get_le32(pb); /* quality */
            ast->sample_size = get_le32(pb); /* sample ssize */
            ast->cum_len *= FFMAX(1, ast->sample_size);
//            av_log(NULL, AV_LOG_DEBUG, "%d %d %d %d\n", ast->rate, ast->scale, ast->start, ast->sample_size);

            switch(tag1) {
            case MKTAG('v', 'i', 'd', 's'):
                codec_type = CODEC_TYPE_VIDEO;

                ast->sample_size = 0;
                break;
            case MKTAG('a', 'u', 'd', 's'):
                codec_type = CODEC_TYPE_AUDIO;
                break;
            case MKTAG('t', 'x', 't', 's'):
                //FIXME
                codec_type = CODEC_TYPE_DATA; //CODEC_TYPE_SUB ?  FIXME
                break;
            default:
                av_log(s, AV_LOG_ERROR, "unknown stream type %X\n", tag1);
                goto fail;
            }
            ast->frame_offset= ast->cum_len;
            url_fskip(pb, size - 12 * 4);
            break;
        case MKTAG('s', 't', 'r', 'f'):
            /* stream header */
            if (stream_index >= (unsigned)s->nb_streams || avi->dv_demux) {
                url_fskip(pb, size);
            } else {
                st = s->streams[stream_index];
                switch(codec_type) {
                case CODEC_TYPE_VIDEO:
                    if(amv_file_format){
                        st->codec->width=avih_width;
                        st->codec->height=avih_height;
                        st->codec->codec_type = CODEC_TYPE_VIDEO;
                        st->codec->codec_id = CODEC_ID_AMV;
                        url_fskip(pb, size);
                        break;
                    }
                    get_le32(pb); /* size */
                    st->codec->width = get_le32(pb);
                    st->codec->height = get_le32(pb);
                    get_le16(pb); /* panes */
                    st->codec->bits_per_sample= get_le16(pb); /* depth */
                    tag1 = get_le32(pb);
                    get_le32(pb); /* ImageSize */
                    get_le32(pb); /* XPelsPerMeter */
                    get_le32(pb); /* YPelsPerMeter */
                    get_le32(pb); /* ClrUsed */
                    get_le32(pb); /* ClrImportant */

                    if (tag1 == MKTAG('D', 'X', 'S', 'B')) {
                        st->codec->codec_type = CODEC_TYPE_SUBTITLE;
                        st->codec->codec_tag = tag1;
                        st->codec->codec_id = CODEC_ID_XSUB;
                        break;
                    }

                    if(size > 10*4 && size<(1<<30)){
                        st->codec->extradata_size= size - 10*4;
                        st->codec->extradata= av_malloc(st->codec->extradata_size + FF_INPUT_BUFFER_PADDING_SIZE);
                        get_buffer(pb, st->codec->extradata, st->codec->extradata_size);
                    }

                    if(st->codec->extradata_size & 1) //FIXME check if the encoder really did this correctly
                        get_byte(pb);

                    /* Extract palette from extradata if bpp <= 8 */
                    /* This code assumes that extradata contains only palette */
                    /* This is true for all paletted codecs implemented in ffmpeg */
                    if (st->codec->extradata_size && (st->codec->bits_per_sample <= 8)) {
                        st->codec->palctrl = av_mallocz(sizeof(AVPaletteControl));
#ifdef WORDS_BIGENDIAN
                        for (i = 0; i < FFMIN(st->codec->extradata_size, AVPALETTE_SIZE)/4; i++)
                            st->codec->palctrl->palette[i] = bswap_32(((uint32_t*)st->codec->extradata)[i]);
#else
                        memcpy(st->codec->palctrl->palette, st->codec->extradata,
                               FFMIN(st->codec->extradata_size, AVPALETTE_SIZE));
#endif
                        st->codec->palctrl->palette_changed = 1;
                    }

#ifdef DEBUG
                    print_tag("video", tag1, 0);
#endif
                    st->codec->codec_type = CODEC_TYPE_VIDEO;
                    st->codec->codec_tag = tag1;
                    st->codec->codec_id = codec_get_id(codec_bmp_tags, tag1);
                    st->need_parsing = AVSTREAM_PARSE_HEADERS; // this is needed to get the pict type which is needed for generating correct pts
//                    url_fskip(pb, size - 5 * 4);
                    break;
                case CODEC_TYPE_AUDIO:
                    get_wav_header(pb, st->codec, size);
                    if(ast->sample_size && st->codec->block_align && ast->sample_size % st->codec->block_align)
                        av_log(s, AV_LOG_DEBUG, "invalid sample size or block align detected\n");
                    if (size%2) /* 2-aligned (fix for Stargate SG-1 - 3x18 - Shades of Grey.avi) */
                        url_fskip(pb, 1);
                    /* Force parsing as several audio frames can be in
                     * one packet and timestamps refer to packet start*/
                    st->need_parsing = AVSTREAM_PARSE_TIMESTAMPS;
                    /* ADTS header is in extradata, AAC without header must be stored as exact frames, parser not needed and it will fail */
                    if (st->codec->codec_id == CODEC_ID_AAC && st->codec->extradata_size)
                        st->need_parsing = AVSTREAM_PARSE_NONE;
                    /* AVI files with Xan DPCM audio (wrongly) declare PCM
                     * audio in the header but have Axan as stream_code_tag. */
                    if (st->codec->stream_codec_tag == ff_get_fourcc("Axan")){
                        st->codec->codec_id  = CODEC_ID_XAN_DPCM;
                        st->codec->codec_tag = 0;
                    }
                    if (amv_file_format)
                        st->codec->codec_id  = CODEC_ID_ADPCM_IMA_AMV;
                    break;
                default:
                    st->codec->codec_type = CODEC_TYPE_DATA;
                    st->codec->codec_id= CODEC_ID_NONE;
                    st->codec->codec_tag= 0;
                    url_fskip(pb, size);
                    break;
                }
            }
            break;
        case MKTAG('i', 'n', 'd', 'x'):
            i= url_ftell(pb);
            if(!url_is_streamed(pb) && !(s->flags & AVFMT_FLAG_IGNIDX)){
                read_braindead_odml_indx(s, 0);
            }
            url_fseek(pb, i+size, SEEK_SET);
            break;
        case MKTAG('I', 'N', 'A', 'M'):
            avi_read_tag(pb, s->title, sizeof(s->title), size);
            break;
        case MKTAG('I', 'A', 'R', 'T'):
            avi_read_tag(pb, s->author, sizeof(s->author), size);
            break;
        case MKTAG('I', 'C', 'O', 'P'):
            avi_read_tag(pb, s->copyright, sizeof(s->copyright), size);
            break;
        case MKTAG('I', 'C', 'M', 'T'):
            avi_read_tag(pb, s->comment, sizeof(s->comment), size);
            break;
        case MKTAG('I', 'G', 'N', 'R'):
            avi_read_tag(pb, s->genre, sizeof(s->genre), size);
            break;
        case MKTAG('I', 'P', 'R', 'D'):
            avi_read_tag(pb, s->album, sizeof(s->album), size);
            break;
        case MKTAG('I', 'P', 'R', 'T'):
            avi_read_tag(pb, str_track, sizeof(str_track), size);
            sscanf(str_track, "%d", &s->track);
            break;
        default:
            if(size > 1000000){
                av_log(s, AV_LOG_ERROR, "well something went wrong during header parsing, "
                                        "ill ignore it and try to continue anyway\n");
                avi->movi_list = url_ftell(pb) - 4;
                avi->movi_end  = url_fsize(pb);
                goto end_of_header;
            }
            /* skip tag */
            size += (size & 1);
            url_fskip(pb, size);
            break;
        }
    }
 end_of_header:
    /* check stream number */
    if (stream_index != s->nb_streams - 1) {
    fail:
        for(i=0;i<s->nb_streams;i++) {
            av_freep(&s->streams[i]->codec->extradata);
            av_freep(&s->streams[i]);
        }
        return -1;
    }

    if(!avi->index_loaded && !url_is_streamed(pb))
        avi_load_index(s);
    avi->index_loaded = 1;
    avi->non_interleaved |= guess_ni_flag(s);
    if(avi->non_interleaved)
        clean_index(s);

    return 0;
}

static int avi_read_packet(AVFormatContext *s, AVPacket *pkt)
{
    AVIContext *avi = s->priv_data;
    ByteIOContext *pb = &s->pb;
    int n, d[8], size;
    offset_t i, sync;
    void* dstr;

    if (ENABLE_DV_DEMUXER && avi->dv_demux) {
        size = dv_get_packet(avi->dv_demux, pkt);
        if (size >= 0)
            return size;
    }

    if(avi->non_interleaved){
        int best_stream_index = 0;
        AVStream *best_st= NULL;
        AVIStream *best_ast;
        int64_t best_ts= INT64_MAX;
        int i;

        for(i=0; i<s->nb_streams; i++){
            AVStream *st = s->streams[i];
            AVIStream *ast = st->priv_data;
            int64_t ts= ast->frame_offset;

            if(ast->sample_size)
                ts /= ast->sample_size;
            ts= av_rescale(ts, AV_TIME_BASE * (int64_t)st->time_base.num, st->time_base.den);

//            av_log(NULL, AV_LOG_DEBUG, "%"PRId64" %d/%d %"PRId64"\n", ts, st->time_base.num, st->time_base.den, ast->frame_offset);
            if(ts < best_ts){
                best_ts= ts;
                best_st= st;
                best_stream_index= i;
            }
        }
        best_ast = best_st->priv_data;
        best_ts= av_rescale(best_ts, best_st->time_base.den, AV_TIME_BASE * (int64_t)best_st->time_base.num); //FIXME a little ugly
        if(best_ast->remaining)
            i= av_index_search_timestamp(best_st, best_ts, AVSEEK_FLAG_ANY | AVSEEK_FLAG_BACKWARD);
        else
            i= av_index_search_timestamp(best_st, best_ts, AVSEEK_FLAG_ANY);

//        av_log(NULL, AV_LOG_DEBUG, "%d\n", i);
        if(i>=0){
            int64_t pos= best_st->index_entries[i].pos;
            pos += best_ast->packet_size - best_ast->remaining;
            url_fseek(&s->pb, pos + 8, SEEK_SET);
//        av_log(NULL, AV_LOG_DEBUG, "pos=%"PRId64"\n", pos);

            assert(best_ast->remaining <= best_ast->packet_size);

            avi->stream_index= best_stream_index;
            if(!best_ast->remaining)
                best_ast->packet_size=
                best_ast->remaining= best_st->index_entries[i].size;
        }
    }

resync:
    if(avi->stream_index >= 0){
        AVStream *st= s->streams[ avi->stream_index ];
        AVIStream *ast= st->priv_data;
        int size;

        if(ast->sample_size <= 1) // minorityreport.AVI block_align=1024 sample_size=1 IMA-ADPCM
            size= INT_MAX;
        else if(ast->sample_size < 32)
            size= 64*ast->sample_size;
        else
            size= ast->sample_size;

        if(size > ast->remaining)
            size= ast->remaining;
        av_get_packet(pb, pkt, size);

        if (ENABLE_DV_DEMUXER && avi->dv_demux) {
            dstr = pkt->destruct;
            size = dv_produce_packet(avi->dv_demux, pkt,
                                    pkt->data, pkt->size);
            pkt->destruct = dstr;
            pkt->flags |= PKT_FLAG_KEY;
        } else {
            /* XXX: how to handle B frames in avi ? */
            pkt->dts = ast->frame_offset;
//                pkt->dts += ast->start;
            if(ast->sample_size)
                pkt->dts /= ast->sample_size;
//av_log(NULL, AV_LOG_DEBUG, "dts:%"PRId64" offset:%"PRId64" %d/%d smpl_siz:%d base:%d st:%d size:%d\n", pkt->dts, ast->frame_offset, ast->scale, ast->rate, ast->sample_size, AV_TIME_BASE, avi->stream_index, size);
            pkt->stream_index = avi->stream_index;

            if (st->codec->codec_type == CODEC_TYPE_VIDEO) {
                AVIndexEntry *e;
                int index;
                assert(st->index_entries);

                index= av_index_search_timestamp(st, pkt->dts, 0);
                e= &st->index_entries[index];

                if(index >= 0 && e->timestamp == ast->frame_offset){
                    if (e->flags & AVINDEX_KEYFRAME)
                        pkt->flags |= PKT_FLAG_KEY;
                }
            } else {
                pkt->flags |= PKT_FLAG_KEY;
            }
            if(ast->sample_size)
                ast->frame_offset += pkt->size;
            else
                ast->frame_offset++;
        }
        ast->remaining -= size;
        if(!ast->remaining){
            avi->stream_index= -1;
            ast->packet_size= 0;
        }

        return size;
    }

    memset(d, -1, sizeof(int)*8);