Building a Linux PVR, Part 2: Microsoft's MCE 2004

Codecs

Unlike MythTV's virtually endless possibilities for using different codecs to transcode audio/video, MCE is designed only record with an MPEG2-based codec with the extension ".dvr-ms". These MPEG2 streams are created specifically with MCE features in mind, such as time shifting, live pause and simultaneously recording, and playing back audio and video. DVR-MS is really nothing more than MPEG2 wrapped in an encrypted ASF wrapper. DVR-MS has 3 quality settings that we mentioned on the previous page.

These .dvr-ms files can be played back on regular Windows XP machines unless they are copy-protected by the broadcaster, in which case they will only be able to play on the original Media Center PC where it was recorded, and only in Windows Media Player, we might add. There are some utilities that will covert dvr-ms files to MPEG2 DVD compliant files, but that is beyond the scope of our topic and is not supported by Microsoft.

Unfortunately, we have a large issue with the amount of disk space that the MPEG2 codec consumes. A 15-minute clip of video can take as much as 400MB. MythTV does not perform much better when video is downloaded at high quality, but we have the option to transcode, or re-render the MPEG stream into something a little more versatile. For example, we can compress our cartoon captures down to a lower quality MPEG1 codec without sacrificing much quality; or with a XviD plugin, we can transcode our entire library into MPEG4 in the background. Note that we are using the same Sempron 3100+ processor in both machines!

In this analysis, we are taking video capture from analog cable. We are able to capture digital cable from a digital cable feed as well, but it requires the MCE machine to use a special IR module that actually controls the digital cable box. This can be done with MythTV under LIRC as well.

A sample clip from MCE 2004.
Click to enlarge.

A close-up from MCE 2004.

Taking a small 200px square sample from the analog cable feed above, we see a bit of interference. This is more of a problem with our cable feed than MCE or MythTV, but on MythTV, we are able to use a lower quality codec to capture or transcode the signal. Using an MPEG2 stream to capture a low quality signal at 1.2GB per hour seems like a ridiculous waste of space. With MythTV, we are given the option to keep this kind of signal as a 480i MPEG1 stream instead.

MythTV's transcoding option.
Click to enlarge.