There are many variables that go into the question: "How fast a CPU do I need to run MythTV"? Obviously, the faster your CPU, the better your experience will be with MythTV. If you are using the software MPEG-4 encoder and performing the "Watch TV" function, where the CPU is both encoding and decoding video simultaneously to allow Pause, Fast Forward and Rewind functions for live TV requires more CPU then just encoding or decoding. MythTV also supports multiple encoder cards in a single PC, thereby increasing the CPU requirements if you plan on simultaneously encoding multiple programs. As a general guideline, plan on 1GHz per encoder if you are doing software-based encoding, less if you are using a hardware-based encoder.
Here are a few data points:
* A PIII/733MHz system can encode one video stream using the MPEG-4 codec using 480x480 capture resolution. This does not allow for live TV watching, but does allow for encoding video and then watching it later.
* A developer states that his AMD1800+ system can almost encode two MPEG-4 video streams and watch one program simultaneously.
* A PIII/800MHz system with 512MB RAM can encode one video stream using the RTjpeg codec with 480x480 capture resolution and play it back simultaneously, thereby allowing live TV watching.
* A dual Celeron/450MHz is able to view a 480x480 MPEG-4/3300kbps file created on a different system with 30% CPU usage.
* A P4 2.4GHz machine can encode two 3300Kbps 480x480 MPEG-4 files and simultaneously serve content to a remote frontend.