RFC 7826 recommends (but does not require) starting at 0,
but at least one known server implementation fails to copy
request sequence numbers <1 into responses due to an
incorrect null check.
The server known to exhibit this behavior is the Parrot
Streaming Server, serving video from their UAV devices.
A fix has been submitted upstream as well:
https://github.com/Parrot-Developers/librtsp/pull/2
The Parrot developers are known to have tested with LibVLC.
In WireShark debugging, LibVLC appears to start with a CSeq
of 2, which is likely why this bug went unnoticed.
This reverts
487595a7d6e2d, which set this to 0 citing the
RFC. The switch to 0 was thus a recent one; it's therefore
possible server implementors relied on the previous
GStreamer client behavior in their tests as well.
Fixes #624.
newconn->url = gst_rtsp_url_copy (url);
newconn->timer = g_timer_new ();
newconn->timeout = 60;
- newconn->cseq = 0; /* RFC 7826: "it is RECOMMENDED to start at 0." */
+ newconn->cseq = 1; /* RFC 7826: "it is RECOMMENDED to start at 0.",
+ but some servers don't copy values <1 due to bugs. */
newconn->remember_session_id = TRUE;