mpeg.c

F:图像处理资料264264书籍ffmpeg-0.4.9-pre1VideoStream.rar 一个视频解压缩源代码

                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 {
                /* AC3 */
                put_byte(&ctx->pb, stream->nb_frames);
                put_be16(&ctx->pb, stream->frame_start_offset);
            }
        }

        /* output data */
        put_buffer(&ctx->pb, stream->buffer, payload_size - stuffing_size);
    }

    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++;
    stream->nb_frames = 0;
    stream->frame_start_offset = 0;
}

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++;
}

static int64_t update_scr(AVFormatContext *ctx,int stream_index,int64_t pts)
{
    MpegMuxContext *s = ctx->priv_data;
    int64_t scr;
    StreamInfo *stream;
    int i;

    if (s->is_vcd) {
        /* 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;


#if 0
        for(i=0;i<ctx->nb_streams;i++) {
            stream = ctx->streams[i]->priv_data;
            
            if(scr > stream->start_pts && stream->start_pts!=AV_NOPTS_VALUE) {
                av_log(ctx, AV_LOG_DEBUG, "mpeg vcd: SCR above PTS (scr=%0.3f, stream index=%d, stream_pts=%0.3f).\n", scr/90000.0, i, stream->start_pts / 90000.0);                 
            }
        }
#endif
    }
    else {
        
        
        /* XXX I believe this calculation of SCR is wrong. SCR
           specifies at which time the data should enter the decoder.
           Two packs cannot enter the decoder at the same time. */

        /* XXX: system clock should be computed precisely, especially for
        CBR case. The current mode gives at least something coherent */
        if (stream_index == s->scr_stream_index
            && pts != AV_NOPTS_VALUE)
            scr = pts;
        else
            scr = s->last_scr;

        /* "Sanity hack": make sure that the SCR does not overtake the pts of
           buffered data that is still waiting to be written.*/
        for(i=0;i<ctx->nb_streams;i++) {
            stream = ctx->streams[i]->priv_data;
            
            if(scr > stream->start_pts && stream->start_pts!=AV_NOPTS_VALUE) {
                /* av_log(ctx, AV_LOG_DEBUG, "mpeg: restricting scr to stream pts (scr=%0.3f, stream index=%d, stream_pts=%0.3f).\n", scr/90000.0, i, stream->start_pts / 90000.0); */
                scr = stream->start_pts;
            }
        }
    }

    s->last_scr=scr;

    return scr;
}    


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, new_start_pts, new_start_dts;
    int len, avail_size;
    
    pts= pkt->pts;
    dts= pkt->dts;

    if(s->is_svcd) {
        /* offset pts and dts slightly into the future to be able
           to do the compatibility fix below.*/
        pts = (pts + 2) & ((1LL << 33) - 1);
        dts = (dts + 2) & ((1LL << 33) - 1);

        if (stream->packet_number == 0 && dts == pts)
            /* For the very first packet we want to force the DTS to be included.
               This increases compatibility with lots of DVD players.
               Since the MPEG-2 standard mandates that DTS is only written when
               it is different from PTS we have to move it slightly into the past.*/
            dts = (dts - 2) & ((1LL << 33) - 1);
    }
    if(s->is_vcd) {
        /* We have to offset the PTS, so that it is consistent with the SCR.
           SCR starts at 36000, but the first two packs contain only padding
           and the first pack from the other stream, respectively, may also have
           been written before.
           So the real data starts at SCR 36000+3*1200. */
        pts = (pts + 36000 + 3600) & ((1LL << 33) - 1);
        dts = (dts + 36000 + 3600) & ((1LL << 33) - 1);
    }
    
#if 0
    update_scr(ctx,stream_index,pts);

    printf("%d: pts=%0.3f dts=%0.3f scr=%0.3f\n", 
           stream_index, 
           pts / 90000.0, 
           dts / 90000.0, 
           s->last_scr / 90000.0);
#endif
    
    /* we assume here that pts != AV_NOPTS_VALUE */
    new_start_pts = stream->start_pts;
    new_start_dts = stream->start_dts;
    
    if (stream->start_pts == AV_NOPTS_VALUE) {
        new_start_pts = pts;
        new_start_dts = dts;
    }
    avail_size = get_packet_payload_size(ctx, stream_index,
                                         new_start_pts, 
                                         new_start_dts);
    if (stream->buffer_ptr >= avail_size) {

        update_scr(ctx,stream_index,stream->start_pts);

        /* unlikely case: outputing the pts or dts increase the packet
           size so that we cannot write the start of the next
           packet. In this case, we must flush the current packet with
           padding.
           Note: this always happens for the first audio and video packet
           in a VCD file, since they do not carry any data.*/
        flush_packet(ctx, stream_index,
                     stream->start_pts, stream->start_dts, s->last_scr);
        stream->buffer_ptr = 0;
    }
    stream->start_pts = new_start_pts;
    stream->start_dts = new_start_dts;
    stream->nb_frames++;
    if (stream->frame_start_offset == 0)
        stream->frame_start_offset = stream->buffer_ptr + 1;
    while (size > 0) {
        avail_size = get_packet_payload_size(ctx, stream_index,
                                             stream->start_pts, 
                                             stream->start_dts);
        len = avail_size - stream->buffer_ptr;
        if (len > size)
            len = size;
        memcpy(stream->buffer + stream->buffer_ptr, buf, len);
        stream->buffer_ptr += len;
        buf += len;
        size -= len;
        if (stream->buffer_ptr >= avail_size) {

            update_scr(ctx,stream_index,stream->start_pts);

            /* if packet full, we send it now */
            flush_packet(ctx, stream_index,
                         stream->start_pts, stream->start_dts, s->last_scr);
            stream->buffer_ptr = 0;

            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->start_pts) ) >= s->packet_size)
                    put_vcd_padding_sector(ctx);
            }

            /* Make sure only the FIRST pes packet for this frame has
               a timestamp */
            stream->start_pts = AV_NOPTS_VALUE;
            stream->start_dts = AV_NOPTS_VALUE;
        }
    }

    return 0;
}

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

    /* flush each packet */
    for(i=0;i<ctx->nb_streams;i++) {
        stream = ctx->streams[i]->priv_data;
        if (stream->buffer_ptr > 0) {
            update_scr(ctx,i,stream->start_pts);

            /* NOTE: we can always write the remaining data as it was
               tested before in mpeg_mux_write_packet() */
            flush_packet(ctx, i, stream->start_pts, stream->start_dts, 
                         s->last_scr);
        }
    }

    /* 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++)
        av_freep(&ctx->streams[i]->priv_data);

    return 0;
}
#endif //CONFIG_ENCODERS

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

#define MAX_SYNC_SIZE 100000

static int mpegps_probe(AVProbeData *p)
{
    int code, c, i;

    code = 0xff;
    /* we search the first start code. If it is a packet start code,
       then we decide it is mpeg ps. We do not send highest value to
       give a chance to mpegts */
    /* NOTE: the search range was restricted to avoid too many false
       detections */

    if (p->buf_size < 6)
        return 0;

    for (i = 0; i < 20; i++) {
        c = p->buf[i];
        code = (code << 8) | c;
        if ((code & 0xffffff00) == 0x100) {
            if (code == PACK_START_CODE ||
                code == SYSTEM_HEADER_START_CODE ||
                (code >= 0x1e0 && code <= 0x1ef) ||
                (code >= 0x1c0 && code <= 0x1df) ||
                code == PRIVATE_STREAM_2 ||
                code == PROGRAM_STREAM_MAP ||
                code == PRIVATE_STREAM_1 ||
                code == PADDING_STREAM)
                return AVPROBE_SCORE_MAX - 2;
            else
                return 0;
        }
    }
    return 0;
}


typedef struct MpegDemuxContext {
    int header_state;
} 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;
    }