[vlc] Re: VLC MPEG2 streaming reception

[Robert.Smith at ses-astra.com]

Hi all,

Here is some additional information to my previous email:

>The interesting thing here is that when I stream this new file using vlc
>(vlc -vvv --extraintf logger axis-es-windows-mplayer.mpg --loop --sout
>#rtp{dst=228.96.1.1,sdp=file://guide5.sdp} ), I can receive it fine using
>mplayer (mplayer sdp://guide5.sdp) but if i try to receive it using vlc
>(vlc -vvv --extraintf logger udp:@228.96.1.1) then I see video corruption.

The original file (axis-es-windows-mplayer.mpg) contains an dump of an RTP
stream containing an MEPG-2 elementary video stream. Obviously if I try to
receive it as UDP instead of RTP, vlc displays the stream incorrectly. I am
actually surprised I see any picture at all.
If I try the reception using the command "vlc rtp:@28.96.1.1:1236" then I
have the same behaviour as with the SDP file, namely the log output shows
"ps warning: garbage at input" messages. The video corruption problem is
therefore a "brain corruption" problem on my part.

There remains the problem of not being able to view the stream using the
SDP file.
A closer look at the log file on the receiver shows the messages:
---
mpgv warning: ES module discarded (no startcode)
sap warning: SDP (UDP) module discarded
livedotcom warning: SDP module discarded
...
ps warning: this does not look like an MPEG PS stream,
continuing anyway
main debug: using demux2 module "ps"
access_udp warning: unimplemented query in control
main debug: `rtp:@:1236' sucessfully opened
ps warning: garbage at input
ps warning: garbage at input
----
I don't understand why the ES and SDP modules are discarded. Surely they
should be used in this case? Is there a way to force vlc to use the "ES"
demux module instead of PS?

BTW, while I was testing, I ran across a couple of anomalies:

1. VLC seems to interpret an SDP file containing a unicast destination
incorrectly

If I create an RTP stream using the command
"vlc axis-es-linux-mplayer.mpg --sout
#rtp{dst=228.96.1.1,sdp=file://guide5.sdp}"
the SDP file looks like this:
v=0
o=- 54114853253 1 IN IP4 127.0.0.1
s=NONE
t=0 0
a=tool:vlc 0.8.2-svn-20050215
c=IN IP4 228.96.1.1/0
m=video 10000 RTP/AVP 32
a=rtpmap:32 MPV/90000
and the player log file looks like this:
main debug: adding playlist item `NONE' ( rtp://@228.96.1.1:10000 )
The player receives the data.

If I create the same stream with a unicast destination
"vlc axis-es-linux-mplayer.mpg --sout
#rtp{dst=10.232.31.1,sdp=file://guide5.sdp}"
the SDP file looks like this
v=0
o=- 54458172939 1 IN IP4 127.0.0.1
s=NONE
t=0 0
a=tool:vlc 0.8.2-svn-20050215
c=IN IP4 10.232.31.1/0
m=video 10000 RTP/AVP 32 a=rtpmap:32 MPV/90000
and the player log file looks like this:
main debug: adding playlist item `NONE' ( rtp://10.232.31.1:10000 )

The missing "@" causes the player to interpret this as a stream from server
10.232.31.1 port 10000 to the local port 1234 (default), and the player
receives no data. It seems the player does not read the SDP file for
unicast streams correctly.

2. "vlc axis-es-linux-mplayer.mpg --sout
#rtp{dst=10.232.31.1,port=10000,sdp=file://guide5.sdp}" creates a unicast
stream with UDP destination port 1236, but
"vlc axis-es-linux-mplayer.mpg --sout
#rtp{dst=10.232.31.1,port-video=10000,sdp=file://guide5.sdp}" creates a
unicast stream with UDP destination port 10000.

I would expect both commands to have the same effect as the input stream is
a single elementary video stream.


best regards,
Robert







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