But there has been one problem that occurs intermittently: the audio on live & recorded programs will sound like it's being projected from a tin can. The sound is discernible, but wrong. Enduring an hour-long program with bad sound can be difficult.

At first, I wasn't sure if the sound distortion was coming from the digital cable box, the PVR-150 encoder card, or MythTV playback. We had never experienced this kind of audio distortion with our old Tivo service using the same digital cable box, so I had to rule out the cable box. Also, we never had any problems when using the PVR-150 tuner input, which combines video & audio in a single input. I had recently switched from the tuner input to the composite audio & video input on the PVR-150 due to the generally higher quality they deliver in comparison to coaxial feeds. So, I concluded that problem was with the PVR-150 composite audio input.

I'd noticed that leaving and then promptly returning to the channel would resolve the problem. But this is not possible when recording programs while away. After reading several posting on MythTV user lists, I decided to modify the channel-change script to fork a background that re-establishes the audio input 2 seconds after the channel-change script returns. This has worked successfully for a week now, which is a marked improvement over where we were.

The following shows the channel-change script:

[scott@eowyn ~]$ cat /usr/local/bin/change_chan.sh 
#!/bin/sh

# send infrared signals to change the current channel
REMOTE_NAME=comcast
for digit in $(echo $1 | sed -e 's/./& /g'); do 
  /usr/local/bin/irsend SEND_ONCE $REMOTE_NAME $digit
  sleep 0.4
done
/usr/local/bin/irsend SEND_ONCE $REMOTE_NAME "ok"

# start audio fix script in the background
/usr/local/bin/ivtv_audio_fix.sh &

And the following shows the contents of the audio fix-it script that runs in the background after the channel-change process has finished.

[scott@eowyn ~]$ cat /usr/local/bin/ivtv_audio_fix.sh 
#!/bin/sh

sleep 2

# reset the audio input to source 1
/usr/local/bin/v4l2-ctl --set-audio-input 1

I'll also mention that I don't notice any glitches in the audio despite the fact that the fix-it script runs 2 seconds after the channel has been changed. ]]> http://urlgrey.net/archives/2008/06/audio_distortio.php http://urlgrey.net/archives/2008/06/audio_distortio.php MythTV Sat, 07 Jun 2008 16:16:43 -0800 I had enabled Open Vsync on our MythTV frontend during the initial configuration with the belief that there couldn't be any harm in adding an additional method of vertical synchronization. I changed my mind when I began noticing strange delays in the video playback on my NVidia FX 5200 with XVMC. After changing channels, there would be about 3-5 glitches in video playback for 30 seconds, followed by okay playback. I was okay with it until we began seeing much more dramatic choppiness in playback coupled with higher CPU utilization (typically 18-20%, but as high as 70%).

I searched the web for the symptoms and saw a lot of people reporting problems with video playback when OpenGL Vsync is enabled (here and here). Since disabling OpenGL Vsync, I've not seen any delays in playback. I might re-enable UseEvents in /etc/X11/xorg.conf, but it's currently set to False.

I found the XvMC section of the MythTV wiki describing how to use X-Video Motion Compensation (XvMC) to utilize hardware acceleration when decoding MPEG-2 video. It actually took me several hours to get XvMC working, but I'll summarize the effective steps below:

First, install the NVidia display driver for Linux. The x.org driver doesn't support XvMC, so there's no way around it. My previous post has information on how to do this.

First, set-up the /etc/X11/xorg.conf file for the NVidia driver. XvMC worked only when NVAGP was set to '1'. You find explanations of these options on the NVidia support site. The relevant section of my /etc/X11/xorg.conf follows:

Section "Device"
    Identifier     "Videocard0"
    Driver         "nvidia"
    Option  "NVAGP"                 "1"
    Option  "NoLogo"                "True"
    Option  "RenderAccel"           "True"
    Option  "XvmcUsesTextures"      "True"
    Option  "UseEdidDpi"            "False"
    Option  "DPI"                   "100 x 100"
    Option  "UseEvents"             "False"
    Option  "DPMS"                  "False"
EndSection

Next, create or edit the file /etc/X11/XvMCConfig. Following are some shell commands that show my system setup:

[scott@eowyn lib]$ cd /usr/lib
[scott@eowyn lib]$ ll libXvMCNVIDIA*
-r--r--r-- 1 root root 152808 2008-03-31 08:47 libXvMCNVIDIA.a
lrwxrwxrwx 1 root root     23 2008-03-31 08:47 libXvMCNVIDIA_dynamic.so.1 -> libXvMCNVIDIA.so.169.12
-rwxr-xr-x 1 root root 139604 2008-03-31 08:47 libXvMCNVIDIA.so.169.12
[scott@eowyn lib]$ cat /etc/X11/XvMCConfig 
libXvMCNVIDIA_dynamic.so.1

To confirm that XvMC is working in X Windows, start up X Windows (i.e. startx), create a shell window and run xdpyinfo to look for the XvMC info:

[scott@eowyn lib]$ xdpyinfo | grep XVideo
     XVideo
     XVideo-MotionCompensation

The next step is to instruct mythfrontend to use XvMC for playback. I did this by choosing a playback profile in the mythfrontend via the Setup -> TV Settings -> Playback menus. The CPU-- profile uses 'ivtv' for Standard Definition (SD) Television, and 'xvmc' for higher definition content. I'm only recording SD content right now, but would like to use 'xvmc' to lower the CPU load. So, I created a new playback profile that uses 'xvmc' for all content.

I'll also mention that the picture became skewed on my 16:9 Sony 32" flat-panel television. I corrected this by adding scaling values of X=2, Y=3 in the Setup -> TV Settings -> Playback menu. This shifted the picture left and down to fill the screen. I'm also using the DVI output of the NVidia FX 5200 card. I've got a DVI-to-HDMI cable that delivers a pure digital signal to the television. The clarity is phenomenal.

After making all of these changes, I was able to confirm that XvMC was in use simply by looking at the CPU utilization of the 'mythfrontend' process with 'top'. Before I enabled XvMC, CPU utilization was at 68-72% when playing video. After switching to XvMC, utilization is merely 18-20%. That's more than a 300% reduction in CPU utilization! Since I use the MythTV machine for the backend and frontend, the reduction in CPU utilization opens up the possibility of adding another encoder card, or running some additional services such as ZoneMinder. ]]> http://urlgrey.net/archives/2008/04/using_xvmc_with.php http://urlgrey.net/archives/2008/04/using_xvmc_with.php MythTV Tue, 01 Apr 2008 11:16:04 -0800 While fine-tuning our MythTV system, I noticed that the default menu-renderer is QT. There's nothing wrong with QT, except that it doesn't offer hardware acceleration that OpenGL does. So, using QT creates a higher system load on the MythTV frontend. This takes away CPU cycles that could be better spent, and provides a UI that is less smooth.

So, I enabled OpenGL menu-rendering for MythTV (0.21) only to find the menu transition taking a horrendous amount of time. There was an OpenGL fade that occurred on each screen transition that would take about 5 second to complete. This is when I realized that I should have installed the vendor's X Windows driver.

My MythTV machine has an NVidia GeForce FX 5200 graphics card installed. It's a few years old, but works perfectly for this purpose: fanless, hardware OpenGL rendering & MPEG-2 decoding, and DVI output. I went to the NVidia support site and downloaded the display driver. I then installed it and marveled at how much it improved everything. The system load was greatly reduced because the OpenGL rendering occurred in hardware, menu navigation was very quick, and a lovely fade effect occurs upon each screen transition.

So, the lesson learned was to install the NVidia display drivers when choosing OpenGL menu rendering with MythTV. OpenGL is a great improvement over QT, and having display drivers that can take advantage of hardware acceleration is a must.

So, tonight I got around to calling Tivo Support to get some answers. First, our Tivo is connected to our home network using a wired Ethernet adapter so there's no chance of signal interference being an issue. Second, I've gone through the steps of forcing Tivo to reconnect to the service looking for an update, and have performed a power-cycle of the Tivo to make sure that memory leaks aren't at fault. Unfortunately, none of these helped. The support person who handled my call looked at all of these facts and said that the only thing I could do was "exchange" our Tivo appliance for another Series 2 model at a cost of $149. We purchased our Tivo for $50. How can Tivo justify the price of $149? I declined the exchange and informed the support person that they had been no help whatsoever, and that paying Tivo over $150 per year for simple television guide data is ridiculous.

I now have additional motivation to get MythTV or another open-source PVR system working. Tivo's business practices impose replacement of perfectly good hardware on their customers. I am nearly certain that the lag in our Tivo has been caused by recent system software upgrades forced by the Tivo company. Tivo has lost my support, and will soon lose me as a customer.

I keep our supplies in 4 medium-sized plastic storage containers. These are lightweight, durable, and water-resistant. While I probably could have used 2 or 3 containers, I found that 4 containers allowed me ample space in each container and the ability to limit the container's contents (i.e. kitchen item, food, etc). All of the containers are kept in our garage. There's no perfect place to keep supplies - must be sheltered from the elements and protected from theft, but not be crushed in an earthquake or other structural failure.

The following is a list of articles and guides that I found useful in deciding what to include in my supplies:

• Ready.gov from FEMA - publication on household preparedness
• American Red Cross - Prepare at Home
• UC Berkeley Office of Emergency Preparedness (earthquake-oriented)
• Daily Kos (5-part series of articles)

Here's the list representing my actual supplies at home:

Emergency Supplies at Home Supplies Sleeping Bags (2) Plastic bucket with lid N95 respirator masks (20) First Aid Kit First Aid Manual Heavy-load Rope (200+ pounds) (3/8" x 100 feet) (2) Light-load Rope (75 pounds) (1/8" x 48 feet) (2) Duffel Bag (2) Lighting Battery-powered Lantern Heavy-Duty Mag Flashlight (D-Cells) Small Flashlight (2) LED Headlamp Chemical Light-sticks (6) (4-year shelf-life) Tea-light Candles (6) 9-hour candles (4) Candle lantern Electricity 50' Power Extension Cord Power Strip with surge protector 400 watt AC inverter in car AA Batteries (20) AAA Batteries (14) C Batteries (6) D Batteries (6) Communications Radio (battery-powered) (AM/FM/Weather/TV) Corded Telephone Portable FRS/GMRS Radios (2) Charger & Rechargeable Batteries for FRS/GMRS Radios Instant Hand Warmers (4) Waterproof Matches (4 boxes) Solar Emergency Blanket (2) Protective goggles (2) Rain Poncho (2) Work Gloves (2) Foam Ear Plugs (2 pair per set) (2 sets) Hammer Crescent Wrench Pliers Plastic Trowel Pens (3) Small notebook Electrical Tape Duct Tape Swiss Army Knife Padlocks with key (2) Playing Cards Plastic tarp Food 3 gallons of water per person (total of 6 gallons) Canned Soup (2) Freeze-dried Ice-cream (2) 72-hour food supply (2) Cat food Veterinarian suggested food (2 cans) Clothing (need more in this area) Sweatshirts (3) Baseball hat Personal Hygiene Toilet Paper (4 rolls) Facial Tissue Moist wipes (50 count) Tums Chewable Antacid Sunscreen SPF-15 (aerosol has longest shelf-life) Insect repellent Antihistamine (Benadryl or similar) Deodorant (2) Disposable Razors (4) Shaving cream Body soap Shampoo Toothbrushes (2) Toothpaste Cooking Propane camping stove Propane fuel canisters (3) Paper plates (54) Paper towels (2 rolls) Aluminum foil (50 square feet) Contractor-grade trash bags for clean-up and sanitation (15 minimum) Manual Can Opener Plastic Cups (50) Plastic Eating-Utensils (16 total) Nalgene bottles (2) Sierra cup (stainless-steel backpacking cup) Katadyn Micropur MP1 water purification tablets (30) Water purification filter Information & Resources Coins & cash Printed Emergency Contacts DVD containing encrypted financial records and home inventory Maps (local and state-wide, free from AAA) San Francisco Bay California Monterey Bay Oakland-Berkeley San Francisco

]]> http://urlgrey.net/archives/2008/03/emergency_prepa.php http://urlgrey.net/archives/2008/03/emergency_prepa.php Emergency Preparedness Sun, 16 Mar 2008 07:34:00 -0800 One of my interests is being prepared for natural and man-made emergencies that may occur in the San Francisco Bay Area. I believe that preparedness should include one's personal finances. Keeping records that are current and available can lead to a quicker recovery and smaller loss.

I have used the Quicken software program from Intuit since 2001 to manage my personal finances. This includes tracking my investments, savings, and monthly bills. Loss or unavailability of Quicken would count as a real emergency for me. For this reason, I make quarterly backups of my Quicken information and keep them off-site

I've decided to use recordable DVDs for my data backups, with the reasons being:

• Highly accessible since most computers contains DVD-ROM drives


• Cheap to produce, at less than $1 per disc (cheaper than magnetic disk drives)


• Resistant to damage from water, magnetic signals, etc (not true for USB flash drives)


• Tamper-proof since the information can't be modified


• Can be encrypted to protect the contents


• Can store up to 8 GB of data, which makes them preferable to CDs.

A popular software program for recording DVDs on the Mac OS X platform is Toast from Roxio. It provides support for encrypted disk images (supported natively in Mac OS X) and disk spanning. I highly recommend it.

The information I include on my backups is:

• VMware Fusion virtual machine of Windows 2003 Server with Quicken program & data


• VMware Fusion installer & se