Mac mini HDTV HTPC Notes - Elgato EyeTV 500 tuner

Here's round two for an HDTV HTPC (High-Definition Television Home-Theater PC).  For the previous round, see my web page of notes on using the FusionHDTVII tuner card.  As mentioned in the previous round, the most important consideration for an HTPC is noise.  While Shuttle XPCs are quieter than your average PC, they still are noisy, especially for the family room.  The noise was enough that my wife continuously asked me to turn it off.  So the HTPC was shut off more than it was on, essentially making it useless for time-shifting HDTV programs.  

Two announcements at MacWorld on January 11, 2005, got me to try again.

1. Elgato enhances HDTV support for the Macintosh
• MWSF: Elgato EyeTV 500 adds digital cable support
2. Apple Introduces Mac mini

Components

Experience and Setup

Elgato EyeTV 500

But we want to view HDTV programs on the big HTDV in the family room.  I used a 17" PowerBook with a 1GHz G4 to view Superbowl XXXIX on February 6, 2005.  The CPU was often pegged and there were occasional CPU overruns that exhibited jerky video where the image would hesitate and speed up, probably with significant frame dropping. It wasn't annoying enough to stop watching. The experience suggested that the Mac mini with its faster 1.42GHz G4 processor could handle the load.

The Mac mini arrived on March 3, 2005.  Apple's setup wizard for the Mac mini includes support for Bluetooth wireless keyboard and mouse; there's no need to have wired devices at hand just to get started!  Setup of the EyeTV 500 was easy as I'd already done it on both the Power Mac and PowerBook.  Copying /Library/Preferences/com.elgato.eyetv.plist from one machine to another works so you don't have to re-enter the channel names.  HDTV viewing was up in minutes with Mac OS / Mac mini / EyeTV 500 as opposed to hours with Windows XP / Shuttle XPC / FusionHDTVII.

M-Audio Transit

It took some web browsing and fiddling to configure the M-Audio Transit correctly.

1. System Preferences > M-Audio Transit USB > Settings > Active Channels: Output to AC-3.
2. System Preferences > Sound > Output > Choose a device for sound output - Name/Port: Headphones / Built-in Audio.
   • Do NOT choose M-Audio Transit USB / USB as the device for system sound output, or you will only get stereo output and will not be able to configure your applications for Dolby digital output.
3. Configure the application for digital audio as follows
1. Quit EyeTV (DVD Player) and restart EyeTV (DVD Player).
   • Applications like EyeTV (DVD Player) seem to check for digital audio only on startup, so if digital audio was not enabled at startup time, it will continue to be disabled.
2. Configure Digital Audio via the menu item Audio > Audio Output > Digital Audio Output.
3. Configure digital audio stream via the menu item Audio > Dolby Digital, or other named stream.
   • The available streams appear by name at the bottom of the Audio menu. The streams may have duplicate or incorrect names, so you should use trial-and-error until you get the best audio for the current program.

Make sure to check the M-Audio site for driver updates. With version 1.5.9, audio output from the Transit would stop under high CPU load, and I would have to switch Audio Output to System Sound Output and then back to Digital Audio Output to get it working again. I just updated to version 1.6 of the driver, and digital audio output has not stopped even with the CPU pegged by simultaneous playback of two or even three programs. I've heard a few audio dropouts, but kudos to M-Audio for improved robustness and performance.

Data Rate/Resolution versus CPU Usage

Q: The EyeTV 500 product requires a "G4 500 MHz or better" processor. Why is that?

A: Decoding MPEG-2 video is a very CPU-intensive task. EyeTV will not be able to decode MPEG-2 content in real-time on a slower processor. It takes a dual processor G5 to display full size, full frame rate HDTV.

The graph shows a scatter plot of 20 programs, labeled by their channel call-sign. The X axis is the datarate, and the Y axis is the CPU usage of EyeTV. The program type is obvious:

• High Definition programs are shown in green for 720p and red for 1080i. They are clearly toward the upper end of the graph, requiring a lot of bandwidth and consuming a lot of CPU for decoding.
• Standard Definition 480p programs are shown in blue, and are clumped around 3Mbps and 25% CPU.
• The audio-only channel is labeled "MC '90s" (Music Choice '90s) in blue. This is an example of an audio-only channel that doesn't have any motion video, just an occasional background image.

For this test, other overhead was WindowServer around 5% and Activity Monitor around 2%. Idle CPU headroom was often in single digits for HD programs.

Our visual experience matches the measurements. The Mac mini can easily handle SD and audio-only programs, and it has enough CPU to decode a single HD program almost all of the time without dropping frames. The headroom is small enough that we do get rare visible CPU overruns.

Other observations:

• Real-time viewing or viewing while recording have similar CPU loads.
• The program stream must be read from the EyeTV 500 tuner, and this firewire IO has some small but significant cost. In both of these cases, the program stream is written to disk. Real-time viewing writes the program to disk so that you can pause or do instant replay.
• Program playback has a lower CPU load than recording or real-time viewing.
  • Playback reads the program stream from disk, but doesn't have any firewire IO to the EyeTV 500 tuner.
• Some applications may have significant load even when idle. Use Activity Monitor to identify non-HDTV applications to quit.
  • Internet Explorer (IE) consumes around 7% CPU just displaying the TitanTV program grid, even when hidden.

Channel Lineup - Comcast of NJ

Video Display

Pending

Conclusion