[FFmpeg-devel] Additional RTSP issues

Luca Abeni lucabe72
Tue Jul 14 17:45:13 CEST 2009

Stas Oskin wrote:
> Hi.
> In addition to the SEQ problem that I'm working on right now, I have other 2
> issues which I might be able to tinker:
> 1) There is a delay between the moment initial connection to RTSP is done
> ,and before the read__packet() returns the first packet. The delay is about
> 2-3 seconds, and then all the packets for these seconds are returned at once
> (one after another), with AV_NOPTS_VALUE for their PTS/DTS value.

This should only happen if you receive a stream that has been started before
the player (basically, you cannot receive reliable timestamps until the first
RTCP SR packet has been received).

> Other RTSP implementation don't seem to have this issue.

Some players return fake timestamps until the first RTCP SR packet is received
(for example, if receiving a multicast stream with "vlc file.sdp" you can see
a discontinuity in the audio or in the video after few seconds).

> Any idea if it's as intended, and there any setting which controls it? If
> not, is it a know issue, which can be solved?

If you are playing an "rtsp://" URL, ensure that the server sends an RTCP SR
packet as soon as the player starts playing the stream.

> 2) It seems that current RTSP implementation doesn't send keep-alive signals

Not sure what a "keep-alive" signal is... Where is it described in the standard?
For sure, the RTCP RR packets sent by libavformat contain unreliable information,
but this seems to be by design.


More information about the ffmpeg-devel mailing list