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Working with fancy displays
A PC stacked full of video isn’t much good without a big display to play it on, which is why my lounge room PC is permanently connected to a 101cm Sony Bravia LCD TV. Like a lot of big shiny TVs, my LCD has a VGA input, which makes hooking up a PC basically no different from any other monitor.
However, your may need to do some tweaking to get the TV running at its native resolution. On my 1366x768 Bravia, this was just a case of adding an appropriate mode to my /etc/X11/xorg.conf file, and changing the display configuration to use that new mode. I’d like to take credit for this, but to be honest, I Googled my TV and found someone else that had already worked out the details. I placed this line in the ‘Monitor’ section of my xorg.conf:
ModeLine “1360x768” 85.500 1360 1424 1536 1792 768 771 777 795 +Hsync +Vsync
Then, I modified the ‘Modes’ line in the ‘Screen’ section to use the new mode:
Modes “1360x768”
Because X likes things to be divisible by 16, 1360 is about as close as you’ll get to the 1366 pixel native width, but the TV just blanks those extra columns, so the pixels still match up 1:1 with the display.
If your TV doesn’t have VGA or DVI inputs, you’ll have to rely on a video card with more TV-compatible outputs: composite, S-video or component. The best advice I can give you on this is to stick with an NVIDIA card, and the proprietary NVIDIA drivers. Most NVIDIA cards from the Geforce 4 models onwards have TV outputs, with the FX5200 and the 6200 being great, affordable choices if you’re buying new. The proprietary drivers from ATI/AMD also offer TV-out support for most Radeon cards.
Some older cards can be made to work, but the time and cost involved in tracking one down and setting it up is quite daunting. A less neat, though more practical solution is to throw hardware at the problem, in the form of an external VGA transcoder box. These convert a VGA input in to a TV-compatible output, and should work perfectly with any video card.
To configure an NVIDIA card, all you should need to do is add two options to the ‘Monitor’ section of your xorg.conf file:
Option “TVStandard” “PAL-B”
Option “ConnectedMonitor” “TV”
The ‘ConnectedMonitor’ option forces output to the TV, even if you still have a monitor attached, which is handy when you’re first setting it up. The driver will automatically work out which display modes will work on the TV-out, so you should get an image up without having to fiddle with the modes. However, a mode like 1024x768 is wasted on a low-resolution device like a normal TV, so it’s best to use a mode like 640x480 or 800x600.
If you’re using a card with component outputs, you may need to change the ‘TVStandard’ option to ‘HD576i’. You can use higher modes as well, like ‘HD720p’ or ‘HD1080i’ if you’re working with a high-definition TV.
If you’re running a widescreen display, your videos may appear squashed or stretched during playback because X doesn’t know the aspect ratio of your display. Like most widescreen TVs, my Bravia has a 16:9 aspect ratio, while my widescreen LCD monitor uses a 16:10 ratio. You can tell X about the aspect ratio of your display by using the ‘DisplaySize’ option, which takes the width and height of your display in millimetres. This goes in the ‘Monitor’ section, and on my Bravia it looks like this:
DisplaySize 880 500
Most players, including Xine, pick up on this automatically, but for some reason MPlayer, which I prefer to use, needs its own configuration. In the
.mplayer/config file in your home directory (just create it if it doesn’t exist), add the ‘monitoraspect’ option:
monitoraspect=16:9
Of course, on my desktop I use ‘16:10’ as the value, to match the display.
Video formats
Just as with compressing audio, there’s a range of codecs available for video compression. Xvid encodes to the MPEG-4 Advanced Simple Profile (ASP), like the commercial DivX codec, but it’s free and open source. Because it’s a compliant MPEG-4 encoder, Xvid files can be played on a wide range of players and devices. Along with its good balance between performance and quality, this makes Xvid a great choice for most needs.
If you really want to minimise your file sizes, you can try the more modern H.264 codec, otherwise known as MPEG-4 Advanced Video Coding (AVC). MEncoder and other tools support H.264 through the x264 encoder. You can get smaller files and better quality than Xvid but at the cost of longer encoding times and greater CPU usage during playback.
However, both MPEG-4 variants are, like MP3, covered by software patents, which puts these codecs in a legal grey area even though the software is free. The patent-free alternative is Ogg Theora, an open source video codec along the lines of the Ogg Vorbis audio codec. Theora is derived from VP3, a proprietary codec from On2 Technologies, which was released as open source in 2001, along with a disclaimer freeing it from On2’s patents. The easiest way to work with it is with ffmpeg2theora, which will convert just about anything to an Ogg file with Theora video and Vorbis audio. However, Theora doesn’t yet perform as well as Xvid, and there are concerns that it never will, at least without using any patented encoding techniques.
This article appeared in the July, 2007 issue of PC Authority.
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