Brian's Brain

Continued from 'Microsoft's Windows Vista: A (Nearly) Perfect Media Center Extension'…

Orb's PR representative, Ron Perrotta, put me in touch with tech support manager William Ndiaye who, after a few preliminary questions, suggested that I override the Dscaler MPEG-2 video filter installed along with Orb and instead select the default Microsoft MPEG-2 filter via Orb's configuration menu. That step wasn't enough, but additionally 'punching the button' in the options screen in order to deinstall DScaler did the trick…at least for video. Now, I couldn't hear the accompanying audio track. That setback was more easily surmounted, as Ndiaye surmised that my tuner card was one of the rare few that output an AC-3 bitstream instead of MPEG audio. Installing AC3Filter therefore did the trick.

The next glitch, while also audio-related, took several hours to solve. I happened to notice that the NBC Olympics broadcasts I'd earlier recorded were playing back in 2-channel Dolby Digital both upstairs and downstairs, even though all of my A/V receiver's speaker lights were illuminated. That was odd, as NBC had previously made a big to-do about its surround sound plans, going so far as to convert 2-channel recordings into pseudo-5.1 (PDF). At first, I thought my two-speaker laptop might be down-mixing the surround source, so I set it to 5.1-channel mode both in the overall Windows and Media Center-specific configuration menus. No improvement.

Next, I remembered that Media Center was doing a one-generation transcode of the incoming MPEG-2 video and Dolby Digital audio source streams, in the process of creating the DVR-MS recording (which I think is the case even in the 'best' quality mode I have been using, though I may be wrong here). I looked at the AC3Filter settings and noticed that this DirectSshow decoder also by default down-mixed the audio to a 2-channel presentation, since (among other things) Orb currently only supports 'stereo' playback. Therefore, I thought by tapping into that same DirectShow filter chain, the DVR-MS transcoder might also be inadvertently down-mixing the incoming audio. Therefore, I de-installed Orb and AC3Filter, and I also found a 5.1 channel audio-inclusive WMV clip which I stored on the Vista-based laptop and subsequently successfully played back in surround over both Xbox 360 Extenders (via a different audio codec, I realized, but still a gratifying proof-of-concept).

The next Olympics broadcast on NBC was set to start at 8PM PT, and at 7:45PM I tuned in a surround audio-inclusive ATSC broadcast from KRXI (Fox) that correctly played back through all six speakers attached to both game consoles. I felt confident I had the problem licked. Imagine my surprise, then, to access the in-progress Olympics recording at 8:30 PM PT and find that it was still in two-channel audio mode! I confirmed that both KRXI and KTVN (CBC) were coming through in surround, both when I watched 'live TV" and when I recorded and then played back short clips. My conclusion at this point is that, for some unknown reason, Reno's NBC affiliate KRNV is broadcasting ATSC (at least the Olympics) in a no-surround down-mix form.

My next issue, I believe, involves available network bandwidth in combination with the quality recording option that I'm employing. A 3-hour 'best' quality recording takes up 19.1 GBytes of HDD space, translating to a 14 Mbps average bitstream size. When you fast-forward through a recording, you periodically get served still shots (i.e. key frames) to show you where you are in the video presentation. The first-level fast forward is only slightly faster than realtime, and the key frames are therefore able to keep up; when I return to 'play' mode I'm usually exactly where the key frames suggest I should be.

Second-level fast-forward is much quicker, but I invariably end up overshooting my key frame-suggested target. Here's an experiment that will quantify the problem. It took 4 minutes and 30 seconds for me to second-level fast-forward through a 3-hour recording. But, once the time graph on the bottom of the Media Center display suggested that I'd reached the end of the clip, successive key frames continued getting served to my eyeballs for another 2+ minutes! I'm surprised that Microsoft isn't giving a more accurate key frame representation of a user's navigation progress by, for example, sensing available network bandwidth to the Extender and accordingly adjusting the key frame delivery rate. With that said, the presence of my bandwidth-gobbling VUDU box isn't making Microsoft's job any easier.

And speaking of network bandwidth, I'll close out this writeup with a related observation. One of the on-site ATSC tuners available for my possible eval is Silicondust's slick HDHomeRun unit. Unlike most PC-targeted products of this nature, it doesn't directly attach to a computer…instead it sits standalone on a LAN and PCs connect to it via software installed on them. Conceptually, this approach is compelling; I can put HDHomeRun near the antenna feed (as long as a means of also tethering it to the LAN is available) and the associated computer(s) can be anywhere LAN-accessible. Plus HDHomeRun has two integrated ATSC tuners, so I can be watching one channel while I'm recording another (or alternatively, two computers can each be simultaneously watching and/or recording different content).

But think about it from a bitrate standpoint. A ~20 Mbps ATSC stream goes from HDHomeRun to a PC, gets transcoded into DVR-MS, then gets simultaneously sent back out by that PC over that same LAN to an Extender such as an Xbox 360. That's a lot of limited LAN bandwidth getting gobbled up. Concurrently utilize HDHomeRun's second tuner and even more precious bandwidth is necessary. It's too bad that Extenders can't directly tap into HDHomeRun's output content, or that I don't have a PC directly connected to my bedroom or living room LCD. but as long as a PC intermediary is involved, a mainstream 100 Mbps CAT5-created LAN will seemingly best-case have barely enough bandwidth to handle a dual-tuner HDHomeRun usage model, and lower-speed wired and wireless LAN technologies will suffer even more. Silicondust customers, I welcome your feedback on whether or not my calculations reflect your hands-on experiences.

p.s...By the way, HDHomeRun is on sale for $138.99 with free shipping at Newegg until midnight tonight, after $30.00-off promo code EMCAJBCAF...

Followup: Had I hit AVSForum from the start, I would have saved myself a lot of debugging trouble...;-)

Followup II: If you'd like to follow in my Media Center Extender footsteps, consider picking up a refurb'd Xbox 360 for $170. Two qualifiers; this first-generation Core system doesn't include a HDMI output (though it offers both component video and VGA options, the latter particularly appealing for its upscaled-DVD compatibility), nor does it include a HDD (which means that the Media Center software gets downloaded each time you attempt to access it...though you can always buy a HDD add-on if the instant-gratification delay becomes too annoying). But the price...goodness gracious!