How to compile Red5 from source?

You need Java SE Development Kit (JDK) and Apache Ant (a Java-based build tool) installed to compile/build Red5 yourself.
What ports are used by Red5 server?

By default Red5 runs under Jetty WebServer and the following ports are used:
RTMP: 1935
RTMPT: 8088
HTTP servlet engine: 5080 (Tomcat uses 8080)
Debug proxy port: 1936

RTMP and RTMPT are protocols for video/audio communication (http://en.wikipedia.org/wiki/Real_Time_Messaging_Protocol). The latter protocol is a wrapper (HTTP tunneling) as a fallback if port 1935 is blocked. The HTTP servlet engine is the ‘webpage’-server like Apache and IIS (Internet Information Server). Normally this service runs on port 80. Finally port 1936 is used. I don’t know its purpose and how to use it.
When I connect from flash to my red5-server-app I get NetConnection.Connect.Failed

Probably another Red5 server is still running (e.g. NT red5 service).
How to fetch the latest source and compile it into a WAR file?

On Linux use the command ‘svn’ (subversion) to obtain the sources and use ‘ant’ (apache ant) to compile to a war file. (Look also in Howtos!)
Is there a way to save an image (screen capture) from Flash using Red5?

There are a bunch of implementations without(!) Red5. The idea is to freeze the local video screen, scan all pixels of the video area in a (byte)array and send (HTTP POST) it to a PHP/JSP/ASP/CFM/… webserver. (Another way for this transport is to stream it (RTMP) to the Red5 server.) On the server the pixels are converted to a jpg or gif and stored as an image file. This works from Flash player 8. A visual example: http://www.bytearray.org/wp-content/uploads/2006/09/media_snapshot/
Complete flash frontend/php backend example by Robert Hall: http://www.ifbin.com/ (look in actionscript -> classes -> flash.display*)
Flash BitmapExporter, Compress and Save Images: http://www.quasimondo.com/archives/000645.php
Png encoder in as3 (Flash 9): http://www.kaourantin.net/2005/10/png-encoder-in-as3.html

Note: the Flash Security Sandbox prevents RTMP streams to be drawn() to BitmapData objects. In AS3 there is a hack possible to circumvent this, but this will probably be fixed in a future update of the Flash player: http://chennney.com/2006/12/08/security-sandbox-violation-bitmapdatadraw-on-rtmp-source/
Converting audio FLV file to MP3?

Once your FLV file gets to the server, you’d presumably like to do something with it. But the FLV is encoded using a format known as NellyMoser. This is a proprietary codec, and no transcodecs are readily available for it.

So that’s where this tool enters the picture. It will convert NellyMoser encoded FLV files to WAV, which you can then convert to MP3 or whatever else you’d like. It works by leveraging the NellyMoser decoder which is compiled into the standard Flash Player.
How do fix NetConnection.Connect.InvalidApp on begining red5 tutorial

would be great if the author provide a downloadable zip or xml file because lot of people get this error even if you follow the tutorial step by step.