udp.c

uclinux 下的vlc播放器源代码

    block_t      *p_block;

    /* Read data */
    p_block = block_New( p_access, p_sys->i_mtu );
    p_block->i_buffer = net_Read( p_access, p_sys->fd, NULL,
                                  p_block->p_buffer, p_sys->i_mtu,
                                  VLC_FALSE );
    if( p_block->i_buffer <= 0 )
    {
        block_Release( p_block );
        return NULL;
    }

    if( (p_block->i_buffer >= p_sys->i_mtu) && p_sys->b_auto_mtu &&
        p_sys->i_mtu < 32767 )
    {
        /* Increase by 100% */
        p_sys->i_mtu *= 2;
        msg_Dbg( p_access, "increasing MTU to %d", p_sys->i_mtu );
    }

    return p_block;
}

/*
 * rtp_ChainInsert - insert a p_block in the chain and
 * look at the sequence numbers.
 */
static inline vlc_bool_t rtp_ChainInsert( access_t *p_access, block_t *p_block )
{
    access_sys_t *p_sys = (access_sys_t *) p_access->p_sys;
    block_t *p_prev = NULL;
    block_t *p = p_sys->p_end;
    uint16_t i_new = (uint16_t) p_block->i_dts;
    uint16_t i_tmp = 0;

    if( !p_sys->p_list )
    {
        p_sys->p_list = p_block;
        p_sys->p_end = p_block;
        return VLC_TRUE;
    }
    /* walk through the queue from top down since the new packet is in 
    most cases just appended to the end */

    for( ;; )
    {
        i_tmp = i_new - (uint16_t) p->i_dts;

        if( !i_tmp )   /* trash duplicate */
            break; 

        if ( i_tmp < 32768 )
        {   /* insert after this block ( i_new > p->i_dts ) */
            p_block->p_next = p->p_next;
            p->p_next = p_block;
            p_block->p_prev = p;
            if (p_prev)
            {
                p_prev->p_prev = p_block;
                msg_Dbg(p_access, "RTP reordering: insert after %d, new %d", 
                    (uint16_t) p->i_dts, i_new );
            }
            else 
            {
                p_sys->p_end = p_block;
            }
            return VLC_TRUE;
        }
        if( p == p_sys->p_list )
        {   /* we've reached bottom of chain */
            i_tmp = p_sys->i_last_seqno - i_new;
            if( !p_access->info.b_prebuffered || (i_tmp > 32767) )
            {
                msg_Dbg(p_access, "RTP reordering: prepend %d before %d", 
                        i_new, (uint16_t) p->i_dts );
                p_block->p_next = p;
                p->p_prev = p_block;
                p_sys->p_list = p_block;
                return VLC_TRUE;
            }

            if( !i_tmp )   /* trash duplicate */
                break;    

            /* reordering failed - append the packet to the end of queue */
            msg_Dbg(p_access, "RTP: sequence changed (or buffer too small) "
                "new: %d, buffer %d...%d", i_new, (uint16_t) p->i_dts, 
                (uint16_t) p_sys->p_end->i_dts);
            p_sys->p_end->p_next = p_block;
            p_block->p_prev = p_sys->p_end;
            p_sys->p_end = p_block;
            return VLC_TRUE;
        }
        p_prev = p;
        p = p->p_prev;
    }
    block_Release( p_block );
    return VLC_FALSE;
}

/*****************************************************************************
 * BlockParseRTP/BlockRTP:
 *****************************************************************************/
static block_t *BlockParseRTP( access_t *p_access, block_t *p_block )
{
    int      i_rtp_version;
    int      i_CSRC_count;
    int      i_payload_type;
    int      i_skip = 0;
    int      i_extension_flag = 0;
    int      i_extension_length = 0;
    uint16_t i_sequence_number = 0;

    if( p_block == NULL )
        return NULL;

    if( p_block->i_buffer < RTP_HEADER_LEN )
        goto trash;

    /* Parse the header and make some verifications.
     * See RFC 3550. */
    i_rtp_version     = ( p_block->p_buffer[0] & 0xC0 ) >> 6;
    i_CSRC_count      = p_block->p_buffer[0] & 0x0F;
    i_extension_flag  = p_block->p_buffer[0] & 0x10;
    i_payload_type    = p_block->p_buffer[1] & 0x7F;
    i_sequence_number = (p_block->p_buffer[2] << 8 ) + p_block->p_buffer[3];

    if( i_rtp_version != 2 )
        msg_Dbg( p_access, "RTP version is %u, should be 2", i_rtp_version );

    if( i_payload_type == 14 || i_payload_type == 32)
        i_skip = 4;
    else if( i_payload_type !=  33 )
        msg_Dbg( p_access, "unsupported RTP payload type (%u)", i_payload_type );
    if( i_extension_flag )
        i_extension_length = 4 +
            4 * ( (p_block->p_buffer[14] << 8) + p_block->p_buffer[15] );

    /* Skip header + CSRC extension field n*(32 bits) + extension */
    i_skip += RTP_HEADER_LEN + 4*i_CSRC_count + i_extension_length;

    if( i_skip >= p_block->i_buffer )
        goto trash;

    /* Return the packet without the RTP header, remember seqno in i_dts */
    p_block->i_buffer -= i_skip;
    p_block->p_buffer += i_skip;
    p_block->i_pts = mdate();
    p_block->i_dts = (mtime_t) i_sequence_number;

#if 0
    /* Emulate packet loss */
    if ( (i_sequence_number % 4000) == 0)
    {
        msg_Warn( p_access, "Emulating packet drop" );
        block_Release( p_block );
        return NULL;
    }
#endif

    return p_block;


trash:
    msg_Warn( p_access, "received a too short packet for RTP" );
    block_Release( p_block );
    return NULL;
}

static block_t *BlockPrebufferRTP( access_t *p_access, block_t *p_block )
{
    access_sys_t *p_sys = p_access->p_sys;
    mtime_t   i_first = mdate();
    int       i_count = 0;
    block_t   *p = p_block;

    for( ;; )
    {
        mtime_t i_date = mdate();

        if( p && rtp_ChainInsert( p_access, p ))
            i_count++;

        /* Require at least 2 packets in the buffer */
        if( i_count > 2 && (i_date - i_first) > p_sys->i_rtp_late )
            break;

        p = BlockParseRTP( p_access, BlockUDP( p_access ));
        if( !p && (i_date - i_first) > p_sys->i_rtp_late ) 
        {
            msg_Err( p_access, "error in RTP prebuffering!" );
            break;
        }
    }

    msg_Dbg( p_access, "RTP: prebuffered %d packets", i_count - 1 );
    p_access->info.b_prebuffered = VLC_TRUE;
    p = p_sys->p_list;
    p_sys->p_list = p_sys->p_list->p_next;
    p_sys->i_last_seqno = (uint16_t) p->i_dts;
    p->p_next = NULL;
    return p;
}

static block_t *BlockRTP( access_t *p_access )
{
    access_sys_t *p_sys = p_access->p_sys;
    block_t *p;

    while ( !p_sys->p_list || 
             ( mdate() - p_sys->p_list->i_pts ) < p_sys->i_rtp_late )
    {
        p = BlockParseRTP( p_access, BlockUDP( p_access ));

        if ( !p ) 
            return NULL;

        rtp_ChainInsert( p_access, p );
    }

    p = p_sys->p_list;
    p_sys->p_list = p_sys->p_list->p_next;
    p_sys->i_last_seqno++;
    if( p_sys->i_last_seqno != (uint16_t) p->i_dts )
    {
        msg_Dbg( p_access, "RTP: packet(s) lost, expected %d, got %d",
                 p_sys->i_last_seqno, (uint16_t) p->i_dts );
        p_sys->i_last_seqno = (uint16_t) p->i_dts;
    }
    p->p_next = NULL;
    return p;
}

/*****************************************************************************
 * BlockChoose: decide between RTP and UDP
 *****************************************************************************/
static block_t *BlockChoose( access_t *p_access )
{
    block_t *p_block;
    int     i_rtp_version;
    int     i_CSRC_count;
    int     i_payload_type;

    if( ( p_block = BlockUDP( p_access ) ) == NULL )
        return NULL;

    if( p_block->p_buffer[0] == 0x47 )
    {
        msg_Dbg( p_access, "detected TS over raw UDP" );
        p_access->pf_block = BlockUDP;
        p_access->info.b_prebuffered = VLC_TRUE;
        return p_block;
    }

    if( p_block->i_buffer < RTP_HEADER_LEN )
        return p_block;

    /* Parse the header and make some verifications.
     * See RFC 3550. */

    i_rtp_version  = ( p_block->p_buffer[0] & 0xC0 ) >> 6;
    i_CSRC_count   = ( p_block->p_buffer[0] & 0x0F );
    i_payload_type = ( p_block->p_buffer[1] & 0x7F );

    if( i_rtp_version != 2 )
    {
        msg_Dbg( p_access, "no supported RTP header detected" );
        p_access->pf_block = BlockUDP;
        p_access->info.b_prebuffered = VLC_TRUE;
        return p_block;
    }

    switch( i_payload_type )
    {
        case 33:
            msg_Dbg( p_access, "detected TS over RTP" );
            p_access->psz_demux = strdup( "ts" );
            break;

        case 14:
            msg_Dbg( p_access, "detected MPEG audio over RTP" );
            p_access->psz_demux = strdup( "mpga" );
            break;

        case 32:
            msg_Dbg( p_access, "detected MPEG video over RTP" );
            p_access->psz_demux = strdup( "mpgv" );
            break;

        default:
            msg_Dbg( p_access, "no RTP header detected" );
            p_access->pf_block = BlockUDP;
            p_access->info.b_prebuffered = VLC_TRUE;
            return p_block;
    }

    if( !BlockParseRTP( p_access, p_block )) return NULL;

    p_access->pf_block = BlockRTP;

    return BlockPrebufferRTP( p_access, p_block );
}