mpeg.c

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    if (s->is_vcd || s->is_mpeg2)
        /* every packet */
        s->pack_header_freq = 1;
    else
        /* every 2 seconds */
        s->pack_header_freq = 2 * bitrate / s->packet_size / 8;

    /* the above seems to make pack_header_freq zero sometimes */
    if (s->pack_header_freq == 0)
       s->pack_header_freq = 1;
    
    if (s->is_mpeg2)
        /* every 200 packets. Need to look at the spec.  */
        s->system_header_freq = s->pack_header_freq * 40;
    else if (s->is_vcd)
        /* the standard mandates that there are only two system headers
           in the whole file: one in the first packet of each stream.
           (see standard p. IV-7 and IV-8) */
        s->system_header_freq = 0x7fffffff;
    else
        s->system_header_freq = s->pack_header_freq * 5;
    
    for(i=0;i<ctx->nb_streams;i++) {
        stream = ctx->streams[i]->priv_data;
        stream->buffer_ptr = 0;
        stream->packet_number = 0;
        stream->start_pts = AV_NOPTS_VALUE;
        stream->start_dts = AV_NOPTS_VALUE;
    }
    s->system_header_size = get_system_header_size(ctx);
    s->last_scr = 0;
    return 0;
 fail:
    for(i=0;i<ctx->nb_streams;i++) {
        av_free(ctx->streams[i]->priv_data);
    }
    return -ENOMEM;
}

static inline void put_timestamp(ByteIOContext *pb, int id, int64_t timestamp)
{
    put_byte(pb, 
             (id << 4) | 
             (((timestamp >> 30) & 0x07) << 1) | 
             1);
    put_be16(pb, (uint16_t)((((timestamp >> 15) & 0x7fff) << 1) | 1));
    put_be16(pb, (uint16_t)((((timestamp) & 0x7fff) << 1) | 1));
}


/* return the number of padding bytes that should be inserted into
   the multiplexed stream.*/
static int get_vcd_padding_size(AVFormatContext *ctx, int64_t pts)
{
    MpegMuxContext *s = ctx->priv_data;
    int pad_bytes = 0;

    if (s->vcd_padding_bitrate > 0 && pts!=AV_NOPTS_VALUE)
    {
        int64_t full_pad_bytes;
        
        full_pad_bytes = (int64_t)((s->vcd_padding_bitrate * (pts / 90000.0)) / 8.0);
        pad_bytes = (int) (full_pad_bytes - s->vcd_padding_bytes_written);

        if (pad_bytes<0)
            /* might happen if we have already padded to a later timestamp. This
               can occur if another stream has already advanced further.*/
            pad_bytes=0;
    }

    return pad_bytes;
}


/* return the exact available payload size for the next packet for
   stream 'stream_index'. 'pts' and 'dts' are only used to know if
   timestamps are needed in the packet header. */
static int get_packet_payload_size(AVFormatContext *ctx, int stream_index,
                                   int64_t pts, int64_t dts)
{
    MpegMuxContext *s = ctx->priv_data;
    int buf_index;
    StreamInfo *stream;

    stream = ctx->streams[stream_index]->priv_data;

    buf_index = 0;
    if (((s->packet_number % s->pack_header_freq) == 0)) {
        /* pack header size */
        if (s->is_mpeg2) 
            buf_index += 14;
        else
            buf_index += 12;
        
        if (s->is_vcd) {
            /* there is exactly one system header for each stream in a VCD MPEG,
               One in the very first video packet and one in the very first
               audio packet (see VCD standard p. IV-7 and IV-8).*/
            
            if (stream->packet_number==0)
                /* The system headers refer only to the stream they occur in,
                   so they have a constant size.*/
                buf_index += 15;

        } else {            
            if ((s->packet_number % s->system_header_freq) == 0)
                buf_index += s->system_header_size;
        }
    }

    if ((s->is_vcd && stream->packet_number==0)
        || (s->is_svcd && s->packet_number==0))
        /* the first pack of each stream contains only the pack header,
           the system header and some padding (see VCD standard p. IV-6) 
           Add the padding size, so that the actual payload becomes 0.*/
        buf_index += s->packet_size - buf_index;
    else {
        /* packet header size */
        buf_index += 6;
        if (s->is_mpeg2) {
            buf_index += 3;
            if (stream->packet_number==0)
                buf_index += 3; /* PES extension */
            buf_index += 1;    /* obligatory stuffing byte */
        }
        if (pts != AV_NOPTS_VALUE) {
            if (dts != pts)
                buf_index += 5 + 5;
            else
                buf_index += 5;

        } else {
            if (!s->is_mpeg2)
                buf_index++;
        }
    
        if (stream->id < 0xc0) {
            /* AC3/LPCM private data header */
            buf_index += 4;
            if (stream->id >= 0xa0) {
                int n;
                buf_index += 3;
                /* NOTE: we round the payload size to an integer number of
                   LPCM samples */
                n = (s->packet_size - buf_index) % stream->lpcm_align;
                if (n)
                    buf_index += (stream->lpcm_align - n);
            }
        }

        if (s->is_vcd && stream->id == AUDIO_ID)
            /* The VCD standard demands that 20 zero bytes follow
               each audio packet (see standard p. IV-8).*/
            buf_index+=20;
    }
    return s->packet_size - buf_index; 
}

/* Write an MPEG padding packet header. */
static int put_padding_header(AVFormatContext *ctx,uint8_t* buf, int full_padding_size)
{
    MpegMuxContext *s = ctx->priv_data;
    int size = full_padding_size - 6;    /* subtract header length */

    buf[0] = (uint8_t)(PADDING_STREAM >> 24);
    buf[1] = (uint8_t)(PADDING_STREAM >> 16);
    buf[2] = (uint8_t)(PADDING_STREAM >> 8);
    buf[3] = (uint8_t)(PADDING_STREAM);
    buf[4] = (uint8_t)(size >> 8);
    buf[5] = (uint8_t)(size & 0xff);

    if (!s->is_mpeg2) {
        buf[6] = 0x0f;
        return 7;
    } else
        return 6;
}

static void put_padding_packet(AVFormatContext *ctx, ByteIOContext *pb,int packet_bytes)
{
    uint8_t buffer[7];
    int size, i;
    
    size = put_padding_header(ctx,buffer, packet_bytes);
    put_buffer(pb, buffer, size);
    packet_bytes -= size;

    for(i=0;i<packet_bytes;i++)
        put_byte(pb, 0xff);
}


/* flush the packet on stream stream_index */
static void flush_packet(AVFormatContext *ctx, int stream_index, 
                         int64_t pts, int64_t dts, int64_t scr)
{
    MpegMuxContext *s = ctx->priv_data;
    StreamInfo *stream = ctx->streams[stream_index]->priv_data;
    uint8_t *buf_ptr;
    int size, payload_size, startcode, id, stuffing_size, i, header_len;
    int packet_size;
    uint8_t buffer[128];
    int zero_trail_bytes = 0;
    int pad_packet_bytes = 0;
    int pes_flags;
    int general_pack = 0;  /*"general" pack without data specific to one stream?*/
    
    id = stream->id;
    
#if 0
    printf("packet ID=%2x PTS=%0.3f\n", 
           id, pts / 90000.0);
#endif

    buf_ptr = buffer;

    if (((s->packet_number % s->pack_header_freq) == 0)) {
        /* output pack and systems header if needed */
        size = put_pack_header(ctx, buf_ptr, scr);
        buf_ptr += size;

        if (s->is_vcd) {
            /* there is exactly one system header for each stream in a VCD MPEG,
               One in the very first video packet and one in the very first
               audio packet (see VCD standard p. IV-7 and IV-8).*/
            
            if (stream->packet_number==0) {
                size = put_system_header(ctx, buf_ptr, id);
                buf_ptr += size;
            }
        } else {
            if ((s->packet_number % s->system_header_freq) == 0) {
                size = put_system_header(ctx, buf_ptr, 0);
                buf_ptr += size;
            }
        }
    }
    size = buf_ptr - buffer;
    put_buffer(&ctx->pb, buffer, size);

    packet_size = s->packet_size - size;

    if (s->is_vcd && id == AUDIO_ID)
        /* The VCD standard demands that 20 zero bytes follow
           each audio pack (see standard p. IV-8).*/
        zero_trail_bytes += 20;
            
    if ((s->is_vcd && stream->packet_number==0)
        || (s->is_svcd && s->packet_number==0)) {
        /* for VCD the first pack of each stream contains only the pack header,
           the system header and lots of padding (see VCD standard p. IV-6).
           In the case of an audio pack, 20 zero bytes are also added at
           the end.*/
        /* For SVCD we fill the very first pack to increase compatibility with
           some DVD players. Not mandated by the standard.*/
        if (s->is_svcd)
            general_pack = 1;    /* the system header refers to both streams and no stream data*/
        pad_packet_bytes = packet_size - zero_trail_bytes;
    }

    packet_size -= pad_packet_bytes + zero_trail_bytes;

    if (packet_size > 0) {

        /* packet header size */
        packet_size -= 6;
        
        /* packet header */
        if (s->is_mpeg2) {
            header_len = 3;
            if (stream->packet_number==0)
                header_len += 3; /* PES extension */
            header_len += 1; /* obligatory stuffing byte */
        } else {
            header_len = 0;
        }
        if (pts != AV_NOPTS_VALUE) {
            if (dts != pts)
                header_len += 5 + 5;
            else
                header_len += 5;
        } else {
            if (!s->is_mpeg2)
                header_len++;
        }

        payload_size = packet_size - header_len;
        if (id < 0xc0) {
            startcode = PRIVATE_STREAM_1;
            payload_size -= 4;
            if (id >= 0xa0)
                payload_size -= 3;
        } else {
            startcode = 0x100 + id;
        }

        stuffing_size = payload_size - stream->buffer_ptr;
        if (stuffing_size < 0)
            stuffing_size = 0;
        if (stuffing_size > 16) {    /*<=16 for MPEG-1, <=32 for MPEG-2*/
            pad_packet_bytes += stuffing_size;
            packet_size -= stuffing_size;
            payload_size -= stuffing_size;
            stuffing_size = 0;
        }

        put_be32(&ctx->pb, startcode);

        put_be16(&ctx->pb, packet_size);
        
        if (!s->is_mpeg2)
            for(i=0;i<stuffing_size;i++)
                put_byte(&ctx->pb, 0xff);

        if (s->is_mpeg2) {
            put_byte(&ctx->pb, 0x80); /* mpeg2 id */

            pes_flags=0;

            if (pts != AV_NOPTS_VALUE) {
                pes_flags |= 0x80;
                if (dts != pts)
                    pes_flags |= 0x40;
            }

            /* Both the MPEG-2 and the SVCD standards demand that the
               P-STD_buffer_size field be included in the first packet of
               every stream. (see SVCD standard p. 26 V.2.3.1 and V.2.3.2
               and MPEG-2 standard 2.7.7) */
            if (stream->packet_number == 0)
                pes_flags |= 0x01;

            put_byte(&ctx->pb, pes_flags); /* flags */
            put_byte(&ctx->pb, header_len - 3 + stuffing_size);

            if (pes_flags & 0x80)  /*write pts*/
                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++)