[vlc] Re: Standardised URL for media streaming ?

[Ross Finlayson]

>Is there a standard way of representing URLs for streaming media sources?

Yes:
         rtsp://<server>:<port>/<streamName>
for RTSP/RTP streams (i.e., streamed from a RTSP server)

>I have the problem of generating generic URLs that are then translated into
>the correct form for each type of player.
>It would make my life easier if there was a standard for such URLs - perhaps
>an RFC

See RFC 2326 <http://www.ietf.org/rfc/rfc2326.txt>.

>For example for multicast udp streams:
>
>VLC => udp://@224.168.100.64:3000
>Moonlight => moonlight://224.168.100.64:3000/udp

These are both bogus, non-standard hacks.  The big problem with 'URLs' like 
this is that they don't convey enough information about the stream.  In 
particular, they don't say anything about what codec(s) are being used, and 
other parameters (e.g., sampling frequency) that are necessary in order for 
the receiver to play the stream.  Often this information is implicit - 
e.g., VLC's "udp://@" URLs will probably work only for MPEG-1 or 2 
Transport or Program Streams.

Also, many streams do not just use a single UDP port; instead, they use 
separate ports for audio and video.  These bogus, non-standard URLs can't 
describe streams like this.  They also can't describe unicast streams that 
are set up on-demand, and whose destination address (and port(s)) vary, 
depending on the receiver.  To play streams like this, you need to first 
communicate with the server - and that's what RTSP is for,

RTSP works by first querying the server (using a "DESCRIBE" command) to get 
information (codecs, sampling frequencies, etc.) that describes the 
stream.  This information is returned in a format called "SDP" ("Session 
Description Protocol" - see RFC 2327).  The RTSP client (i.e., media 
player) then issues RTSP "SETUP" and "PLAY" commands to start playing the 
media stream.

For some streams - in particular, multicast streams - you don't need to use 
RTSP to get the SDP information (because the stream's IP address and port 
number is the same for all recipients).  In this case, the media player 
client can just read a local SDP file instead.

Fortunately, VLC now supports both "rtsp://" URLs, and reading from local 
SDP files.  (Because of this, I hope that support for non-standard hacks 
like "udp://@" URLs can someday be removed.)


	Ross Finlayson
	LIVE.COM
	<http://www.live.com/>

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