mpeg.c

ffmpeg源码分析

    int max_size, start_code;

    max_size = *size_ptr;
    pos_start = url_ftell(pb);

    /* in order to go faster, we fill the buffer */
    pos = pos_start - 16386;
    if (pos < 0)
        pos = 0;
    url_fseek(pb, pos, SEEK_SET);
    get_byte(pb);

    pos = pos_start;
    for(;;) {
        pos--;
        if (pos < 0 || (pos_start - pos) >= max_size) {
            start_code = -1;
            goto the_end;
        }
        url_fseek(pb, pos, SEEK_SET);
        start_code = get_be32(pb);
        if ((start_code & 0xffffff00) == 0x100)
            break;
    }
 the_end:
    *size_ptr = pos_start - pos;
    return start_code;
}
#endif

/**
 * Extracts stream types from a program stream map
 * According to ISO/IEC 13818-1 ('MPEG-2 Systems') table 2-35
 *
 * @return number of bytes occupied by PSM in the bitstream
 */
static long mpegps_psm_parse(MpegDemuxContext *m, ByteIOContext *pb)
{
    int psm_length, ps_info_length, es_map_length;

    psm_length = get_be16(pb);
    get_byte(pb);
    get_byte(pb);
    ps_info_length = get_be16(pb);

    /* skip program_stream_info */
    url_fskip(pb, ps_info_length);
    es_map_length = get_be16(pb);

    /* at least one es available? */
    while (es_map_length >= 4){
        unsigned char type = get_byte(pb);
        unsigned char es_id = get_byte(pb);
        uint16_t es_info_length = get_be16(pb);
        /* remember mapping from stream id to stream type */
        m->psm_es_type[es_id] = type;
        /* skip program_stream_info */
        url_fskip(pb, es_info_length);
        es_map_length -= 4 + es_info_length;
    }
    get_be32(pb); /* crc32 */
    return 2 + psm_length;
}

/* read the next PES header. Return its position in ppos
   (if not NULL), and its start code, pts and dts.
 */
static int mpegps_read_pes_header(AVFormatContext *s,
                                  int64_t *ppos, int *pstart_code,
                                  int64_t *ppts, int64_t *pdts)
{
    MpegDemuxContext *m = s->priv_data;
    int len, size, startcode, c, flags, header_len;
    int64_t pts, dts, last_pos;

    last_pos = -1;
 redo:
        /* next start code (should be immediately after) */
        m->header_state = 0xff;
        size = MAX_SYNC_SIZE;
        startcode = find_next_start_code(&s->pb, &size, &m->header_state);
    //printf("startcode=%x pos=0x%Lx\n", startcode, url_ftell(&s->pb));
    if (startcode < 0)
        return AVERROR_IO;
    if (startcode == PACK_START_CODE)
        goto redo;
    if (startcode == SYSTEM_HEADER_START_CODE)
        goto redo;
    if (startcode == PADDING_STREAM ||
        startcode == PRIVATE_STREAM_2) {
        /* skip them */
        len = get_be16(&s->pb);
        url_fskip(&s->pb, len);
        goto redo;
    }
    if (startcode == PROGRAM_STREAM_MAP) {
        mpegps_psm_parse(m, &s->pb);
        goto redo;
    }

    /* find matching stream */
    if (!((startcode >= 0x1c0 && startcode <= 0x1df) ||
          (startcode >= 0x1e0 && startcode <= 0x1ef) ||
          (startcode == 0x1bd)))
        goto redo;
    if (ppos) {
        *ppos = url_ftell(&s->pb) - 4;
    }
    len = get_be16(&s->pb);
    pts = AV_NOPTS_VALUE;
    dts = AV_NOPTS_VALUE;
    /* stuffing */
    for(;;) {
        if (len < 1)
            goto redo;
        c = get_byte(&s->pb);
        len--;
        /* XXX: for mpeg1, should test only bit 7 */
        if (c != 0xff)
            break;
    }
    if ((c & 0xc0) == 0x40) {
        /* buffer scale & size */
        if (len < 2)
            goto redo;
        get_byte(&s->pb);
        c = get_byte(&s->pb);
        len -= 2;
    }
    if ((c & 0xf0) == 0x20) {
        if (len < 4)
            goto redo;
        dts = pts = get_pts(&s->pb, c);
        len -= 4;
    } else if ((c & 0xf0) == 0x30) {
        if (len < 9)
            goto redo;
        pts = get_pts(&s->pb, c);
        dts = get_pts(&s->pb, -1);
        len -= 9;
    } else if ((c & 0xc0) == 0x80) {
        /* mpeg 2 PES */
        if ((c & 0x30) != 0) {
            /* Encrypted multiplex not handled */
            goto redo;
        }
        flags = get_byte(&s->pb);
        header_len = get_byte(&s->pb);
        len -= 2;
        if (header_len > len)
            goto redo;
        if ((flags & 0xc0) == 0x80) {
            dts = pts = get_pts(&s->pb, -1);
            if (header_len < 5)
                goto redo;
            header_len -= 5;
            len -= 5;
        } if ((flags & 0xc0) == 0xc0) {
            pts = get_pts(&s->pb, -1);
            dts = get_pts(&s->pb, -1);
            if (header_len < 10)
                goto redo;
            header_len -= 10;
            len -= 10;
        }
        len -= header_len;
        while (header_len > 0) {
            get_byte(&s->pb);
            header_len--;
        }
    }
    else if( c!= 0xf )
        goto redo;

    if (startcode == PRIVATE_STREAM_1 && !m->psm_es_type[startcode & 0xff]) {
        if (len < 1)
            goto redo;
        startcode = get_byte(&s->pb);
        len--;
        if (startcode >= 0x80 && startcode <= 0xbf) {
            /* audio: skip header */
            if (len < 3)
                goto redo;
            get_byte(&s->pb);
            get_byte(&s->pb);
            get_byte(&s->pb);
            len -= 3;
        }
    }
    if(dts != AV_NOPTS_VALUE && ppos){
        int i;
        for(i=0; i<s->nb_streams; i++){
            if(startcode == s->streams[i]->id) {
                av_add_index_entry(s->streams[i], *ppos, dts, 0, 0, AVINDEX_KEYFRAME /* FIXME keyframe? */);
            }
        }
    }

    *pstart_code = startcode;
    *ppts = pts;
    *pdts = dts;
    return len;
}

static int mpegps_read_packet(AVFormatContext *s,
                              AVPacket *pkt)
{
    MpegDemuxContext *m = s->priv_data;
    AVStream *st;
    int len, startcode, i, type, codec_id = 0, es_type;
    int64_t pts, dts, dummy_pos; //dummy_pos is needed for the index building to work

 redo:
    len = mpegps_read_pes_header(s, &dummy_pos, &startcode, &pts, &dts);
    if (len < 0)
        return len;

    /* now find stream */
    for(i=0;i<s->nb_streams;i++) {
        st = s->streams[i];
        if (st->id == startcode)
            goto found;
    }

    es_type = m->psm_es_type[startcode & 0xff];
    if(es_type > 0){
        if(es_type == STREAM_TYPE_VIDEO_MPEG1){
            codec_id = CODEC_ID_MPEG2VIDEO;
            type = CODEC_TYPE_VIDEO;
        } else if(es_type == STREAM_TYPE_VIDEO_MPEG2){
            codec_id = CODEC_ID_MPEG2VIDEO;
            type = CODEC_TYPE_VIDEO;
        } else if(es_type == STREAM_TYPE_AUDIO_MPEG1 ||
                  es_type == STREAM_TYPE_AUDIO_MPEG2){
            codec_id = CODEC_ID_MP3;
            type = CODEC_TYPE_AUDIO;
        } else if(es_type == STREAM_TYPE_AUDIO_AAC){
            codec_id = CODEC_ID_AAC;
            type = CODEC_TYPE_AUDIO;
        } else if(es_type == STREAM_TYPE_VIDEO_MPEG4){
            codec_id = CODEC_ID_MPEG4;
            type = CODEC_TYPE_VIDEO;
        } else if(es_type == STREAM_TYPE_VIDEO_H264){
            codec_id = CODEC_ID_H264;
            type = CODEC_TYPE_VIDEO;
        } else if(es_type == STREAM_TYPE_AUDIO_AC3){
            codec_id = CODEC_ID_AC3;
            type = CODEC_TYPE_AUDIO;
        } else {
            goto skip;
        }
    } else if (startcode >= 0x1e0 && startcode <= 0x1ef) {
        type = CODEC_TYPE_VIDEO;
        codec_id = CODEC_ID_MPEG2VIDEO;
    } else if (startcode >= 0x1c0 && startcode <= 0x1df) {
        type = CODEC_TYPE_AUDIO;
        codec_id = CODEC_ID_MP2;
    } else if (startcode >= 0x80 && startcode <= 0x87) {
        type = CODEC_TYPE_AUDIO;
        codec_id = CODEC_ID_AC3;
    } else if (startcode >= 0x88 && startcode <= 0x9f) {
        type = CODEC_TYPE_AUDIO;
        codec_id = CODEC_ID_DTS;
    } else if (startcode >= 0xa0 && startcode <= 0xbf) {
        type = CODEC_TYPE_AUDIO;
        codec_id = CODEC_ID_PCM_S16BE;
    } else if (startcode >= 0x20 && startcode <= 0x3f) {
        type = CODEC_TYPE_SUBTITLE;
        codec_id = CODEC_ID_DVD_SUBTITLE;
    } else {
    skip:
        /* skip packet */
        url_fskip(&s->pb, len);
        goto redo;
    }
    /* no stream found: add a new stream */
    st = av_new_stream(s, startcode);
    if (!st)
        goto skip;
    st->codec->codec_type = type;
    st->codec->codec_id = codec_id;
    if (codec_id != CODEC_ID_PCM_S16BE)
        st->need_parsing = 1;
 found:
    if(st->discard >= AVDISCARD_ALL)
        goto skip;
    if (startcode >= 0xa0 && startcode <= 0xbf) {
        int b1, freq;

        /* for LPCM, we just skip the header and consider it is raw
           audio data */
        if (len <= 3)
            goto skip;
        get_byte(&s->pb); /* emphasis (1), muse(1), reserved(1), frame number(5) */
        b1 = get_byte(&s->pb); /* quant (2), freq(2), reserved(1), channels(3) */
        get_byte(&s->pb); /* dynamic range control (0x80 = off) */
        len -= 3;
        freq = (b1 >> 4) & 3;
        st->codec->sample_rate = lpcm_freq_tab[freq];
        st->codec->channels = 1 + (b1 & 7);
        st->codec->bit_rate = st->codec->channels * st->codec->sample_rate * 2;
    }
    av_new_packet(pkt, len);
    get_buffer(&s->pb, pkt->data, pkt->size);
    pkt->pts = pts;
    pkt->dts = dts;
    pkt->stream_index = st->index;
#if 0
    av_log(s, AV_LOG_DEBUG, "%d: pts=%0.3f dts=%0.3f size=%d\n",
           pkt->stream_index, pkt->pts / 90000.0, pkt->dts / 90000.0, pkt->size);
#endif

    return 0;
}

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

static int64_t mpegps_read_dts(AVFormatContext *s, int stream_index,
                               int64_t *ppos, int64_t pos_limit)
{
    int len, startcode;
    int64_t pos, pts, dts;

    pos = *ppos;
#ifdef DEBUG_SEEK
    printf("read_dts: pos=0x%llx next=%d -> ", pos, find_next);
#endif
    url_fseek(&s->pb, pos, SEEK_SET);
    for(;;) {
        len = mpegps_read_pes_header(s, &pos, &startcode, &pts, &dts);
        if (len < 0) {
#ifdef DEBUG_SEEK
            printf("none (ret=%d)\n", len);
#endif
            return AV_NOPTS_VALUE;
        }
        if (startcode == s->streams[stream_index]->id &&
            dts != AV_NOPTS_VALUE) {
            break;
        }
        url_fskip(&s->pb, len);
    }
#ifdef DEBUG_SEEK
    printf("pos=0x%llx dts=0x%llx %0.3f\n", pos, dts, dts / 90000.0);
#endif
    *ppos = pos;
    return dts;
}

#ifdef CONFIG_MUXERS
static AVOutputFormat mpeg1system_mux = {
    "mpeg",
    "MPEG1 System format",
    "video/mpeg",
    "mpg,mpeg",
    sizeof(MpegMuxContext),
    CODEC_ID_MP2,
    CODEC_ID_MPEG1VIDEO,
    mpeg_mux_init,
    mpeg_mux_write_packet,
    mpeg_mux_end,
};

static AVOutputFormat mpeg1vcd_mux = {
    "vcd",
    "MPEG1 System format (VCD)",
    "video/mpeg",
    NULL,
    sizeof(MpegMuxContext),
    CODEC_ID_MP2,
    CODEC_ID_MPEG1VIDEO,
    mpeg_mux_init,
    mpeg_mux_write_packet,
    mpeg_mux_end,
};

static AVOutputFormat mpeg2vob_mux = {
    "vob",
    "MPEG2 PS format (VOB)",
    "video/mpeg",
    "vob",
    sizeof(MpegMuxContext),
    CODEC_ID_MP2,
    CODEC_ID_MPEG2VIDEO,
    mpeg_mux_init,
    mpeg_mux_write_packet,
    mpeg_mux_end,
};

/* Same as mpeg2vob_mux except that the pack size is 2324 */
static AVOutputFormat mpeg2svcd_mux = {
    "svcd",
    "MPEG2 PS format (VOB)",
    "video/mpeg",
    "vob",
    sizeof(MpegMuxContext),
    CODEC_ID_MP2,
    CODEC_ID_MPEG2VIDEO,
    mpeg_mux_init,
    mpeg_mux_write_packet,
    mpeg_mux_end,
};

/*  Same as mpeg2vob_mux except the 'is_dvd' flag is set to produce NAV pkts */
static AVOutputFormat mpeg2dvd_mux = {
    "dvd",
    "MPEG2 PS format (DVD VOB)",
    "video/mpeg",
    "dvd",
    sizeof(MpegMuxContext),
    CODEC_ID_MP2,
    CODEC_ID_MPEG2VIDEO,
    mpeg_mux_init,
    mpeg_mux_write_packet,
    mpeg_mux_end,
};

#endif //CONFIG_MUXERS

AVInputFormat mpegps_demux = {
    "mpeg",
    "MPEG PS format",
    sizeof(MpegDemuxContext),
    mpegps_probe,
    mpegps_read_header,
    mpegps_read_packet,
    mpegps_read_close,
    NULL, //mpegps_read_seek,
    mpegps_read_dts,
    .flags = AVFMT_SHOW_IDS,
};

int mpegps_init(void)
{
#ifdef CONFIG_MUXERS
    av_register_output_format(&mpeg1system_mux);
    av_register_output_format(&mpeg1vcd_mux);
    av_register_output_format(&mpeg2vob_mux);
    av_register_output_format(&mpeg2svcd_mux);
    av_register_output_format(&mpeg2dvd_mux);
#endif //CONFIG_MUXERS
    av_register_input_format(&mpegps_demux);
    return 0;
}