Re: FYI: Using Squid as a Real Audio/Video works...

On Tue 8 Jul, 1997, Rodney van den Oever <roever@nse.simac.nl> wrote:
>Using the Preferences->Transport tab I selected 'Use specified transports'
>and with the 'Specified Transports' button I selected use 'HTTP Only'.

The RealPlayer (and RealPlayer Plus) manual states:

   Use HTTP Only
                  Select this option if you are behind a firewall and
                  cannot receive data through TCP. All data will be
                  streamed through HTTP.

                  Note: You may not be able to receive some content if
                  you select this option.

Its intent seems to be for those that have no other way of accessing the
realaudio files from a realaudio server (ie. no suitable proxy at their
firewall.) It's a new option, introduced with the release of version 4 players,
and version 4 servers.

>POST http://204.236.7.10/SmpDsBhgRl
>GET http://204.236.7.10/SmpDsBhgRld63e90e5-f7c1-11d0-fcb0-d91ef0931437?1="1"

Again, from the documentation:
  RealPlayer 4.0 identifies itself to the firewall when making a request
  for content to a RealServer. The following string is attached to any
  URL that the Player requests using HTTP GET:

     /SmpDsBhgRl

  Thus, to identify an HTTP GET request from the RealPlayer, look for:

     http://[^/]+/SmpDsBhgRl

  The Player can also be identified by the mime type in a POST to the
  RealServer. The RealPlayer POST has the following mime type:

     "application/x-pncmd"

Note that the first request was a POST, and the second has a '?' in the URL, so
standard Squid configurations would treat it as non-cacheable. It also looks
rather 'magic'.

To try and clarify:

HTTP is an alternative delivery mechanism introduced with version 3 players,
and it allows a reasonable approximation to "streaming" data - that is playing
it as you receive it. More details on that are available at
<URL:http://www.real.com/products/encoder/realvideo/httpstream.html>

It isn't available in the general case: only if someone has made the realaudio
file available via an HTTP server, or they're using a version 4 server, they've
switched it on, and you're using a version 4 client. If someone has made the
file available via their HTTP server, then it'll be cacheable. Otherwise, it
won't be (as far as we can tell.)

The more common RealAudio link connects via their own 'pnm:' method and is
transferred using their proprietary protocol (via TCP or UDP) and not using
HTTP. It can't be cached nor proxied by Squid, and requires something such as
the simple proxy that Progressive Networks themselves have made available, if
you're in a firewall/no direct route situation. Their product does not cache
(and I don't know of any software available that does.)

Some confusion arises because there is also a configuration option to use an
HTTP proxy (such as Squid) with the Realaudio/RealVideo players. This is
because the players can fetch the ".ram" file that contains the 'pnm:'
reference for the audio/video stream. They fetch that .ram file from an HTTP
server, using HTTP.

James.
Received on Tue Jul 08 1997 - 17:34:26 MDT