Mark Turner dot Net

I’ve been resigned lately to having my Myth Frontend not keep pace on playing back HDTV content. My theory has been that the laptop PC I’ve set up for this task is just not peppy enough.

Well, today the kids were watching the latest NOVA episode and I noticed that the every-two-second blip seemed to sometimes stop for 10 or more seconds at a time. The content, however, seemed to be just as intense as before. This seemed to tell me that the frontend hardware is capable of keeping up with the HD stream but something else is keeping it from doing so.

I’ll have to investigate all the little performance tweaks for the frontend to see what might be the magic step.

A few months ago I bought a used motherboard with the goal of upgrading my MythTV backend. The upgrade went smoothly from a hardware and operating system point of view but Myth was never the same for some reason. Adding to the confusion was that I could tune and watch channels using the command-line tool mplayer but Myth would never properly scan channels.

After a little tinkering (and Googling) yesterday, I decided to try increasing the scanning timeouts using MythTV-setup. Where the previous 3 second timeout was once adequate, I bumped both the tuning and signal timeouts to 10 seconds. By feeding the channels.conf file I created using atscscan, I avoided having Myth tune through all 83 channels. That mitigated the pain of the longer timeouts. Presto! I successfully added the channels back into Myth.

And boy, do they look good. The previous HDTV signals were good, but they were also spotty. Now that the digital antennas have claimed the top spots on the stations’ transmission towers, the digital signals are coming in rock solid.

Myth should save our sanity a bit at home, as the kids can now watch something other than the DVD shows they’ve seen 1,000 times already!

Ever since I upgraded to an HD capture card in my MythTV backend, I’ve noticed a wide variation in the playback speeds of the recordings it makes. Some play back at normal speed while others play back far too slowly or quickly. It’s frustrating.

I was going to blame MythTV for this craziness until I remembered the dvb-utils application azap. This little app tunes the HD card and dumps the output to a pipe, thus it provides a way of testing the card (and driver) outside of Myth. I’ve never used it before but it seems to be the perfect test tool. It turns out the streams produced by the driver and card exhibit the same synchronization issues I’ve seen in Myth itself. That means Myth isn’t to blame.

But what is? My card or its driver? I suppose the next step is to somehow get Windows running on my server long enough to test the card using the Windows driver. If that works, I know Linux or the Linux driver is to blame.

The investigation continues…

Last night I took another hack at getting MythTV working with my DVB card. This time I was much more successful! The key was configuring Myth to use the LNB, which was hidden in the mythtv-setup under “capture cards-DiSEqC options. An LNB is not a DiSEqC, so I would’ve never thought to look there, but there it was.
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Yesterday’s space shuttle launch finally motivated me to dust off my DVB-S card and set up satellite reception in our new home. I’d put it off for almost a year, thinking the tree cover in our back yard was too extensive to find a good shot at the sky. It turns out I discovered a very nice spot right on our back deck, so Travis and I spent a little time building a temporary stand for a dish, aiming it, and threading the cable back into our network closet. After a few duh moments where I shook off the cobwebs covering my knowledge of DVB-S, I got reception of the NASA channel – only three hours after the shuttle launched! Better late than never.

Even so, I wasn’t able to get Myth to pull down video for some reason. The dvb-utils applications can tune (and capture) the streams just fine, but Myth just shows a blank screen – even though it can tune the channel and see a signal from the transponder. I don’t know what else I can tinker with to get Myth working with it but I’ll keep hacking at it.