Archive for the ‘home theater’ Category

Using MythTV to display HD recordings on an HDTV set

Thursday, January 3rd, 2008

I’ve been working with digital TV for almost four years now. I first started using it to feed my TiVo a digital signal to kill analog ghosts by downconverting a high-def signal to standard definition for my TiVo. A few months later, I built my built my first MythTV system to record the full high-definition signal. Even though I have been recording high-definition TV broadcasts for three years, I have only begun displaying the recordings in high-definition this week.

One of my holiday presents to myself was a Sony KDS-50A3000 HDTV. I love it. It’s vibrant, has wide viewing angles, and a ton of inputs. I anticipated being able to push a DVI signal to one of the three available HDMI inputs. After ordering an DVI-to-HDMI cable from Blue Jeans Cable, it was time to get everything going.

Displaying HDTV is remarkably easy with recent nVidia drivers under Linux. In the recent (8xxx) builds, there are predefined modes for HD: “1920x1080_60i” is 1080i, “1920x1080_60” is 1080p, and so on. They go in the Display section of xorg.conf.

SubSection “Display”
Depth 16
# Standard modes for computer workstations
#Modes “1024×768″”800×600” and “640×480”
# New modes for HDTV — 1080p, 1080i, 720p, 480p
Modes “1920x1080_60” “1920x1080_60i” “1280x720_60” “720x480_60”

All is well and good. After running the cable from the DVI port to the HDMI input and restarting the X server, the TV reports that I’m giving it a 720p signal. I have HD, but not at the TV’s native resolution. A check of the log shows me why:

(WW) NVIDIA(0): No valid modes for “1920x1080_60”; removing.
(WW) NVIDIA(0): No valid modes for “1920x1080_60i”; removing.
(II) NVIDIA(0): Validated modes:
(II) NVIDIA(0): “1280x720_60”
(II) NVIDIA(0): “720x480_60”

Something is wrong with the 1080p and 1080i modes. The MythTV system is still using the GeForce FX5200 card, which is perfectly competent to drive any SDTV display, but many posts indicate it has problems pushing 1080i out the DVI port.

So, it’s time to get down and dirty. Running Xorg -logverbose 10 -probeonly will cause the server to dump everything. It’s interesting reading.

First of all, I note that the card is detected correctly, and, though it’s a bit confusing, the FX5200 has a maximum pixel clock of 135 MHz. (As an aside, a 135 MHz is sufficient to do 1280×1024@75 Hz.)

(–) NVIDIA(0): Connected display device(s) on GeForce FX 5200 at PCI:1:0:0:
(–) NVIDIA(0): Sony TV XV (DFP-0)
(–) NVIDIA(0): Sony TV XV (DFP-0): 135.0 MHz maximum pixel clock

A bit further down, the server probes the TV using the Extended Display Information Data (EDID) protocol. In the section it reports, I learn that it wasn’t made long before I bought it, and that it really, really wants to be fed a signal with a 60 Hz refresh rate.

(–) NVIDIA(0): — EDID for Sony TV XV (DFP-0) —
(–) NVIDIA(0): EDID Version : 1.3
(–) NVIDIA(0): Manufacturer : SNY
(–) NVIDIA(0): Monitor Name : Sony TV XV
(–) NVIDIA(0): Product ID : 33536
(–) NVIDIA(0): 32-bit Serial Number : xxxxxxxx
(–) NVIDIA(0): Serial Number String :
(–) NVIDIA(0): Manufacture Date : 2007, week 36
(–) NVIDIA(0): DPMS Capabilities :
(–) NVIDIA(0): Prefer first detailed timing : Yes
(–) NVIDIA(0): Supports GTF : No
(–) NVIDIA(0): Maximum Image Size : 1600mm x 900mm
(–) NVIDIA(0): Valid HSync Range : 15 kHz – 70 kHz
(–) NVIDIA(0): Valid VRefresh Range : 58 Hz – 62 Hz
(–) NVIDIA(0): EDID maximum pixel clock : 150.0 MHz

Continuing down the log, I see why the 1080p mode was rejected. 1080p requires that you feed the TV pixels at almost 150 MHz, which is too fast for the pixel clock:

(II) NVIDIA(0): Validating Mode “1920×1080”:
(II) NVIDIA(0): 1920 x 1080 @ 60 Hz
(II) NVIDIA(0): Mode Source: EDID
(II) NVIDIA(0): Pixel Clock : 148.50 MHz
(II) NVIDIA(0): HRes, HSyncStart : 1920, 2008
(II) NVIDIA(0): HSyncEnd, HTotal : 2052, 2200
(II) NVIDIA(0): VRes, VSyncStart : 1080, 1084
(II) NVIDIA(0): VSyncEnd, VTotal : 1089, 1125
(II) NVIDIA(0): H/V Polarity : +/+
(WW) NVIDIA(0): Mode is rejected: PixelClock (148.5 MHz) too high for
(WW) NVIDIA(0): Display Device (Max: 135.0 MHz).

However, the 1080i mode is rejected because the interlaced mode is

(II) NVIDIA(0): Validating Mode “1920×1080”:
(II) NVIDIA(0): 1920 x 540 @ 60 Hz
(II) NVIDIA(0): Mode Source: EDID
(II) NVIDIA(0): Pixel Clock : 74.18 MHz
(II) NVIDIA(0): HRes, HSyncStart : 1920, 2008
(II) NVIDIA(0): HSyncEnd, HTotal : 2052, 2200
(II) NVIDIA(0): VRes, VSyncStart : 540, 542
(II) NVIDIA(0): VSyncEnd, VTotal : 547, 562
(II) NVIDIA(0): H/V Polarity : +/+
(II) NVIDIA(0): Extra : Interlaced
(WW) NVIDIA(0): Mode is rejected: VertRefresh (120.0 Hz) out of range
(WW) NVIDIA(0): (58.000-62.000 Hz).

By adding 120 Hz as a refresh rate and overriding the information from the display, I could push a 1080i signal to the TV. However, what I found is that a 720p signal on MythTV looked awful when converted by MythTV to 1080i. There is some loss of picture quality when displaying a 1080i signal as 720p, but it is much less noticeable. Therefore, I will stick with 720p until I can figure out how to switch video modes on the fly between 1080i and 720p.

New TV furniture has yet to catch up with new TVs

Monday, October 29th, 2007

One of the reasons why I’ve delayed buying a big-screen TV is trying to figure out how to store it. I’ve yet to find a way to store a big-screen TV that meets my requirements:

  1. Material and construction. No metal-and-glass here in earthquake country! The furniture should be made of wood. I’d strongly prefer that it not be a particle-board veneer, but that’s because most veneers are cheap. A high-quality real wood veneer, as opposed to a “wood-esque” plastic coating might work. Wall-mount brackets are a strong plus near to the Pacific Subduction Zone, too.
  2. Color. If we’re talking wood, I like dark colors. A deep red cherry stain is ideal, but that seems impossible unless I build the thing myself and pick out the stain color.
  3. Doors. It’d be nice to be able to close the doors on the TV and hide it from the world. Even with the existing small (20 inch!) set, it feels like the room is built around it. That feeling is only going to be worse with a large set.
  4. TV Size. I keep dancing around which TV to get, but I’m leaning towards the Sony SXRD line. I don’t need the ninja-rific space-savings of LCD or plasma, so I’d rather get an RPTV at half the price. In the Sony SXRD lineup, there are variety of TVs available in the 50″ to 60″ range. As much as I’d like to get an XBR-series TV, the only one in the current model lineup is a 70″ TV, set to come out next spring. I’m going to draw the line at a TV that has a diagonal that is almost my size. (I am 74 inches tall.) There’s a minor constraint here, in that the TV shelf needs to support about 80 pounds and have a shelf depth of about 16 inches, but most furniture easily accomodates that.
  5. Home Theater and Audio/Visual component size. This seems to be the biggest problem I have. Two of my components require a very deep shelf of about twenty inches, and they’re both vital components. One is the Yamaha A/V receiver, and the other is a home theater PC running MythTV. If they were unimportant components, I’d let it go and consider using a small rack of components to the side of the TV. However, the receiver is the hub of the system, and it’s pretty rare to use the TV without pulling the signal from the MythTV machine (whether live TV, time-shifted HDTV recordings, or DVDs). Both of the problematic components need to be accomodated in my storage unit.
  6. Reasonable ventilation. Stereo components hate heat. Computers hate it even worse. If the MythTV computer is getting stored in an enclosure, it’s going to have to stay ventilated to avoid disk failure. (Thankfully, I can use lm_sensors to monitor temperatures.)
  7. Cost. Oh, and in addition to being demanding on what I want, I don’t want to pay a lot, either. Preferably, it doesn’t cost more than the TV that it’s holding. Between the changes in TV, and the changes in video technology, I can’t feel comfortable buying a really expensive piece of furniture that will hold today’s technology. Any TV furniture that’s more than a few years old is great for 4:3 aspect ratio TVs, but I find that nearly everything I watch these days is letterboxed to 16:9. I wouldn’t want to bet on technology staying the same, so I’d like to feel comfortable replacing it.