The Mac mini as a Media Computer

Limitations of iRecord & AV/C Browser

Despite the fact that they work quite well, there are a number of limitations to both of the programs that we looked at from the standpoint of being used as a DVR:

1. Lack of Guide Functionality - while iRecord is able to record on a schedule, neither iRecord or the AV/C Browser have any knowledge of what's actually airing in your area. For this, you'll have to turn to TV Guide online or TitanTV. There is potential for this sort of functionality to get integrated; however, that would fall on a developer to build up enough interest to do so.
2. No Preview while Recording – You have to be pretty confident that what you're recording is what you want to be recording because neither of these programs offer a preview of what you're recording. You can view the transport stream as it is being recorded, and Patrick Edson also has a plugin for VLC that lets you watch what's on a channel without actually recording it.
3. No 5C Encryption Support - Content that has 5C encryption enabled will not be playable, although it will appear to record fine. This will vary from one cable area to the next, but this type of content should primarily be premium channels (e.g. HBO HD). Although, we have seen situations where SD channels also appeared to have 5C encryption enabled.

Other limitations are ones that are surmountable. The data size issue can be worked with as you can always transcode the MPEG-2 transport stream to a smaller format, e.g. DivX. If you are familiar with AppleScript, you can actually build off of the FireWire SDK to add more functionality, which is how many of the initial Virtual D-VHS projects were done.

Performance on the Mac mini

Recording performance is absolutely a non-issue on the mini, since there's no decoding going on. Just simply write the MPEG-2 transport stream to your hard disk. Even when recording the highest bitrate HD streams, we didn't see CPU utilization go higher than 3% on our 1.25GHz Mac mini.

The problem, however, is that we haven't been able to find any applications that offer hardware accelerated MPEG-2 transport stream playback. It seems that the best application for playing back these transport streams natively is VLC (also available for the PC), which doesn't have any sort of hardware decode acceleration support. The end result is that anything above a 13Mbps stream ends up dropping frames on the 1.25GHz Mac mini, meaning that basically all HD streams are unplayable on the mini even though they record fine. The only solution here is to transcode the transport stream to something playable (e.g. DivX) before using your mini as a playback device, which is obviously a lot more work. Another option is to use only the mini as a capture device, and send the transport stream to a fileserver elsewhere in your house for playback or transcoding. The ideal solution would be to have a player that properly took advantage of the hardware, as the 1.25GHz G4 should be enough to playback the MPEG-2 transport stream. Currently, such a solution doesn’t exist for OS X.

Regardless, as impressive as the development support has been around DVR enablement on the mini (and OS X in general), it's still far from complete and far from polished.