mpeg.c

ffmpeg源码分析

                put_timestamp(&ctx->pb, (pes_flags & 0x40) ? 0x03 : 0x02, pts);
            if (pes_flags & 0x40)  /*write dts*/
                put_timestamp(&ctx->pb, 0x01, dts);

            if (pes_flags & 0x01) {  /*write pes extension*/
                put_byte(&ctx->pb, 0x10); /* flags */

                /* P-STD buffer info */
                if (id == AUDIO_ID)
                    put_be16(&ctx->pb, 0x4000 | stream->max_buffer_size/128);
                else
                    put_be16(&ctx->pb, 0x6000 | stream->max_buffer_size/1024);
            }

        } else {
            if (pts != AV_NOPTS_VALUE) {
                if (dts != pts) {
                    put_timestamp(&ctx->pb, 0x03, pts);
                    put_timestamp(&ctx->pb, 0x01, dts);
                } else {
                    put_timestamp(&ctx->pb, 0x02, pts);
                }
            } else {
                put_byte(&ctx->pb, 0x0f);
            }
        }

        if (s->is_mpeg2) {
            /* special stuffing byte that is always written
               to prevent accidental generation of start codes. */
            put_byte(&ctx->pb, 0xff);

            for(i=0;i<stuffing_size;i++)
                put_byte(&ctx->pb, 0xff);
        }

        if (startcode == PRIVATE_STREAM_1) {
            put_byte(&ctx->pb, id);
            if (id >= 0xa0) {
                /* LPCM (XXX: check nb_frames) */
                put_byte(&ctx->pb, 7);
                put_be16(&ctx->pb, 4); /* skip 3 header bytes */
                put_byte(&ctx->pb, stream->lpcm_header[0]);
                put_byte(&ctx->pb, stream->lpcm_header[1]);
                put_byte(&ctx->pb, stream->lpcm_header[2]);
            } else if (id >= 0x40) {
                /* AC3 */
                put_byte(&ctx->pb, nb_frames);
                put_be16(&ctx->pb, trailer_size+1);
            }
        }

        /* output data */
        if(put_fifo(&ctx->pb, &stream->fifo, payload_size - stuffing_size, &stream->fifo.rptr) < 0)
            return -1;
    }else{
        payload_size=
        stuffing_size= 0;
    }

    if (pad_packet_bytes > 0)
        put_padding_packet(ctx,&ctx->pb, pad_packet_bytes);

    for(i=0;i<zero_trail_bytes;i++)
        put_byte(&ctx->pb, 0x00);

    put_flush_packet(&ctx->pb);

    s->packet_number++;

    /* only increase the stream packet number if this pack actually contains
       something that is specific to this stream! I.e. a dedicated header
       or some data.*/
    if (!general_pack)
        stream->packet_number++;

    return payload_size - stuffing_size;
}

static void put_vcd_padding_sector(AVFormatContext *ctx)
{
    /* There are two ways to do this padding: writing a sector/pack
       of 0 values, or writing an MPEG padding pack. Both seem to
       work with most decoders, BUT the VCD standard only allows a 0-sector
       (see standard p. IV-4, IV-5).
       So a 0-sector it is...*/

    MpegMuxContext *s = ctx->priv_data;
    int i;

    for(i=0;i<s->packet_size;i++)
        put_byte(&ctx->pb, 0);

    s->vcd_padding_bytes_written += s->packet_size;

    put_flush_packet(&ctx->pb);

    /* increasing the packet number is correct. The SCR of the following packs
       is calculated from the packet_number and it has to include the padding
       sector (it represents the sector index, not the MPEG pack index)
       (see VCD standard p. IV-6)*/
    s->packet_number++;
}

#if 0 /* unused, remove? */
static int64_t get_vcd_scr(AVFormatContext *ctx,int stream_index,int64_t pts)
{
    MpegMuxContext *s = ctx->priv_data;
    int64_t scr;

        /* Since the data delivery rate is constant, SCR is computed
           using the formula C + i * 1200 where C is the start constant
           and i is the pack index.
           It is recommended that SCR 0 is at the beginning of the VCD front
           margin (a sequence of empty Form 2 sectors on the CD).
           It is recommended that the front margin is 30 sectors long, so
           we use C = 30*1200 = 36000
           (Note that even if the front margin is not 30 sectors the file
           will still be correct according to the standard. It just won't have
           the "recommended" value).*/
        scr = 36000 + s->packet_number * 1200;

    return scr;
}
#endif

static int remove_decoded_packets(AVFormatContext *ctx, int64_t scr){
//    MpegMuxContext *s = ctx->priv_data;
    int i;

    for(i=0; i<ctx->nb_streams; i++){
        AVStream *st = ctx->streams[i];
        StreamInfo *stream = st->priv_data;
        PacketDesc *pkt_desc= stream->predecode_packet;

        while(pkt_desc && scr > pkt_desc->dts){ //FIXME > vs >=
            if(stream->buffer_index < pkt_desc->size ||
               stream->predecode_packet == stream->premux_packet){
                av_log(ctx, AV_LOG_ERROR, "buffer underflow\n");
                break;
            }
            stream->buffer_index -= pkt_desc->size;

            stream->predecode_packet= pkt_desc->next;
            av_freep(&pkt_desc);
        }
    }

    return 0;
}

static int output_packet(AVFormatContext *ctx, int flush){
    MpegMuxContext *s = ctx->priv_data;
    AVStream *st;
    StreamInfo *stream;
    int i, avail_space, es_size, trailer_size;
    int best_i= -1;
    int best_score= INT_MIN;
    int ignore_constraints=0;
    int64_t scr= s->last_scr;
    PacketDesc *timestamp_packet;
    const int64_t max_delay= av_rescale(ctx->max_delay, 90000, AV_TIME_BASE);

retry:
    for(i=0; i<ctx->nb_streams; i++){
        AVStream *st = ctx->streams[i];
        StreamInfo *stream = st->priv_data;
        const int avail_data=  fifo_size(&stream->fifo, stream->fifo.rptr);
        const int space= stream->max_buffer_size - stream->buffer_index;
        int rel_space= 1024*space / stream->max_buffer_size;
        PacketDesc *next_pkt= stream->premux_packet;

        /* for subtitle, a single PES packet must be generated,
           so we flush after every single subtitle packet */
        if(s->packet_size > avail_data && !flush
           && st->codec->codec_type != CODEC_TYPE_SUBTITLE)
            return 0;
        if(avail_data==0)
            continue;
        assert(avail_data>0);

        if(space < s->packet_size && !ignore_constraints)
            continue;

        if(next_pkt && next_pkt->dts - scr > max_delay)
            continue;

        if(rel_space > best_score){
            best_score= rel_space;
            best_i = i;
            avail_space= space;
        }
    }

    if(best_i < 0){
        int64_t best_dts= INT64_MAX;

        for(i=0; i<ctx->nb_streams; i++){
            AVStream *st = ctx->streams[i];
            StreamInfo *stream = st->priv_data;
            PacketDesc *pkt_desc= stream->predecode_packet;
            if(pkt_desc && pkt_desc->dts < best_dts)
                best_dts= pkt_desc->dts;
        }

#if 0
        av_log(ctx, AV_LOG_DEBUG, "bumping scr, scr:%f, dts:%f\n",
               scr/90000.0, best_dts/90000.0);
#endif
        if(best_dts == INT64_MAX)
            return 0;

        if(scr >= best_dts+1 && !ignore_constraints){
            av_log(ctx, AV_LOG_ERROR, "packet too large, ignoring buffer limits to mux it\n");
            ignore_constraints= 1;
        }
        scr= FFMAX(best_dts+1, scr);
        if(remove_decoded_packets(ctx, scr) < 0)
            return -1;
        goto retry;
    }

    assert(best_i >= 0);

    st = ctx->streams[best_i];
    stream = st->priv_data;

    assert(fifo_size(&stream->fifo, stream->fifo.rptr) > 0);

    assert(avail_space >= s->packet_size || ignore_constraints);

    timestamp_packet= stream->premux_packet;
    if(timestamp_packet->unwritten_size == timestamp_packet->size){
        trailer_size= 0;
    }else{
        trailer_size= timestamp_packet->unwritten_size;
        timestamp_packet= timestamp_packet->next;
    }

    if(timestamp_packet){
//av_log(ctx, AV_LOG_DEBUG, "dts:%f pts:%f scr:%f stream:%d\n", timestamp_packet->dts/90000.0, timestamp_packet->pts/90000.0, scr/90000.0, best_i);
        es_size= flush_packet(ctx, best_i, timestamp_packet->pts, timestamp_packet->dts, scr, trailer_size);
    }else{
        assert(fifo_size(&stream->fifo, stream->fifo.rptr) == trailer_size);
        es_size= flush_packet(ctx, best_i, AV_NOPTS_VALUE, AV_NOPTS_VALUE, scr, trailer_size);
    }

    if (s->is_vcd) {
        /* Write one or more padding sectors, if necessary, to reach
           the constant overall bitrate.*/
        int vcd_pad_bytes;

        while((vcd_pad_bytes = get_vcd_padding_size(ctx,stream->premux_packet->pts) ) >= s->packet_size){ //FIXME pts cannot be correct here
            put_vcd_padding_sector(ctx);
            s->last_scr += s->packet_size*90000LL / (s->mux_rate*50LL); //FIXME rounding and first few bytes of each packet
        }
    }

    stream->buffer_index += es_size;
    s->last_scr += s->packet_size*90000LL / (s->mux_rate*50LL); //FIXME rounding and first few bytes of each packet

    while(stream->premux_packet && stream->premux_packet->unwritten_size <= es_size){
        es_size -= stream->premux_packet->unwritten_size;
        stream->premux_packet= stream->premux_packet->next;
    }
    if(es_size)
        stream->premux_packet->unwritten_size -= es_size;

    if(remove_decoded_packets(ctx, s->last_scr) < 0)
        return -1;

    return 1;
}

static int mpeg_mux_write_packet(AVFormatContext *ctx, AVPacket *pkt)
{
    MpegMuxContext *s = ctx->priv_data;
    int stream_index= pkt->stream_index;
    int size= pkt->size;
    uint8_t *buf= pkt->data;
    AVStream *st = ctx->streams[stream_index];
    StreamInfo *stream = st->priv_data;
    int64_t pts, dts;
    PacketDesc *pkt_desc;
    const int preload= av_rescale(ctx->preload, 90000, AV_TIME_BASE);
    const int is_iframe = st->codec->codec_type == CODEC_TYPE_VIDEO && (pkt->flags & PKT_FLAG_KEY);

    pts= pkt->pts;
    dts= pkt->dts;

    if(pts != AV_NOPTS_VALUE) pts += preload;
    if(dts != AV_NOPTS_VALUE) dts += preload;

//av_log(ctx, AV_LOG_DEBUG, "dts:%f pts:%f flags:%d stream:%d nopts:%d\n", dts/90000.0, pts/90000.0, pkt->flags, pkt->stream_index, pts != AV_NOPTS_VALUE);
    if (!stream->premux_packet)
        stream->next_packet = &stream->premux_packet;
    *stream->next_packet=
    pkt_desc= av_mallocz(sizeof(PacketDesc));
    pkt_desc->pts= pts;
    pkt_desc->dts= dts;
    pkt_desc->unwritten_size=
    pkt_desc->size= size;
    if(!stream->predecode_packet)
        stream->predecode_packet= pkt_desc;
    stream->next_packet= &pkt_desc->next;

    fifo_realloc(&stream->fifo, fifo_size(&stream->fifo, NULL) + size + 1);

    if (s->is_dvd){
        if (is_iframe && (s->packet_number == 0 || (pts - stream->vobu_start_pts >= 36000))) { // min VOBU length 0.4 seconds (mpucoder)
            stream->fifo_iframe_ptr = stream->fifo.wptr;
            stream->align_iframe = 1;
            stream->vobu_start_pts = pts;
        } else {
            stream->align_iframe = 0;
        }
    }

    fifo_write(&stream->fifo, buf, size, &stream->fifo.wptr);

    for(;;){
        int ret= output_packet(ctx, 0);
        if(ret<=0)
            return ret;
    }
}

static int mpeg_mux_end(AVFormatContext *ctx)
{
//    MpegMuxContext *s = ctx->priv_data;
    StreamInfo *stream;
    int i;

    for(;;){
        int ret= output_packet(ctx, 1);
        if(ret<0)
            return ret;
        else if(ret==0)
            break;
    }

    /* End header according to MPEG1 systems standard. We do not write
       it as it is usually not needed by decoders and because it
       complicates MPEG stream concatenation. */
    //put_be32(&ctx->pb, ISO_11172_END_CODE);
    //put_flush_packet(&ctx->pb);

    for(i=0;i<ctx->nb_streams;i++) {
        stream = ctx->streams[i]->priv_data;

        assert(fifo_size(&stream->fifo, stream->fifo.rptr) == 0);
        fifo_free(&stream->fifo);
    }
    return 0;
}
#endif //CONFIG_MUXERS

/*********************************************/
/* demux code */

#define MAX_SYNC_SIZE 100000

static int mpegps_probe(AVProbeData *p)
{
    uint32_t code= -1;
    int sys=0, pspack=0, priv1=0, vid=0;
    int i;

    for(i=0; i<p->buf_size; i++){
        code = (code<<8) + p->buf[i];
        if ((code & 0xffffff00) == 0x100) {
            switch(code){
            case SYSTEM_HEADER_START_CODE:    sys++; break;
            case         PRIVATE_STREAM_1:  priv1++; break;
            case          PACK_START_CODE: pspack++; break;
            case       (VIDEO_ID + 0x100):    vid++; break;
            }
        }
    }
    if(sys && sys*9 <= pspack*10)
        return AVPROBE_SCORE_MAX/2+2; // +1 for .mpg
    if((priv1 || vid) && (priv1+vid)*9 <= pspack*10)
        return AVPROBE_SCORE_MAX/2+2; // +1 for .mpg
    return 0;
}


typedef struct MpegDemuxContext {
    int header_state;
    unsigned char psm_es_type[256];
} MpegDemuxContext;

static int mpegps_read_header(AVFormatContext *s,
                              AVFormatParameters *ap)
{
    MpegDemuxContext *m = s->priv_data;
    m->header_state = 0xff;
    s->ctx_flags |= AVFMTCTX_NOHEADER;

    /* no need to do more */
    return 0;
}

static int64_t get_pts(ByteIOContext *pb, int c)
{
    int64_t pts;
    int val;

    if (c < 0)
        c = get_byte(pb);
    pts = (int64_t)((c >> 1) & 0x07) << 30;
    val = get_be16(pb);
    pts |= (int64_t)(val >> 1) << 15;
    val = get_be16(pb);
    pts |= (int64_t)(val >> 1);
    return pts;
}

static int find_next_start_code(ByteIOContext *pb, int *size_ptr,
                                uint32_t *header_state)
{
    unsigned int state, v;
    int val, n;

    state = *header_state;
    n = *size_ptr;
    while (n > 0) {
        if (url_feof(pb))
            break;
        v = get_byte(pb);
        n--;
        if (state == 0x000001) {
            state = ((state << 8) | v) & 0xffffff;
            val = state;
            goto found;
        }
        state = ((state << 8) | v) & 0xffffff;
    }
    val = -1;
 found:
    *header_state = state;
    *size_ptr = n;
    return val;
}

#if 0 /* unused, remove? */
/* XXX: optimize */
static int find_prev_start_code(ByteIOContext *pb, int *size_ptr)
{
    int64_t pos, pos_start;