Hi, All
I think I have found a bug with live555 library which is used in VLC
media player. When it' playing a RTSP stream from the MediaServer, I drag the
slider to a new position but an error occurs : The slider will no longer move,
while the video and audio still run correctly. (the tsx file is right there,
and sequential playing is no problem). So I say, the live555 library with the
client is not able to 'SEEK' to a position.
The cause is located in MediaSubsession::getNormalPlayTime() ,
MediaSession.cpp. Look at this line:
u_int32_t timestampOffset = rtpSource()->curPacketRTPTimestamp()
- rtpInfo.timestamp;
In the suitation of 'SEEKING', it will not work because rtpInfo.timestamp will
be larger than curPacketRTPTimestamp. According to RFC 2326, the media server
echo a reply in response of 'PLAY' with the timestamp and seq_num. And should
it be noted that the seq_num can be something in the future. So current RTP
packet's timestamp maybe smaller than the rtpInfo.timestamp.
A solution to this problem can be just add a judgement before compute
the new fNPT_PTS_Offset:
..........................
if (rtpInfo.infoIsNew) {
if(rtpSource()->curPacketRTPSeqNum() < rtpInfo.seqNum) return -0.1; //
add this line
u_int32_t timestampOffset = rtpSource()->curPacketRTPTimestamp() -
rtpInfo.timestamp;
double nptOffset =
(timestampOffset/(double)(rtpSource()->timestampFrequency()))*scale();
..........................
Then the VLC media will work fine.
John. ShaoFa
2010-9-9
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