I'm not sure about other platforms but on my Windows 64 bit box here's what I did:
ffmpeg - go to
http://ffmpeg.zeranoe.com/builds/ and download the latest static build for your system. This site is for Windows builds. Check
http://www.ffmpeg.org/download.html for other OS's. I just extracted the ffmpeg.exe and replaced the file in C:\Subsonic\transcode
After installing the newer ffmpeg it started using more than one core if needed to keep up with the transcoding. All my spinning wheels stopped and everything ran smooth as glass. I have lots of video on my site if you want to see the results. Link is at the bottom.
I'm also using JW 5.7
To update JW Player to the newest version, go to
http://forum.subsonic.org/forum/viewtopic.php?t=5977
and read the instructions. Read the whole thread as you'll see there is the long way and the short way. I use the method I suggested as it seemed to be less time consuming. IF I want to know what version of the player I'm running, I'll just fo a right click on the installed player and it will tell me what version it is.
I just downloaded JW 5.7, extract player.swf, rename it to the current name in the subsonic/jetty/xxxx/webapp/flash folder and replace the original file. Rename JW Player 5.4 to Old JW Player 5.4. then drop player.swf into the directory and rename it to JW Player 5.4 when you're done it'll be named 5.4 but if you right click on it in SS you'll se that it's really 5.7