Leigh Dyer lets rip on digital TV, video conversion tools, aspect ratios and video formats.
Digital TV is great: the quality is great, the hardware is cheap and it’s not too tricky to get running on your Linux box. With some time and effort you can even turn a Linux box into a full on-demand digital video recorder using MythTV, but for today, we’ll focus on getting a digital tuner working and recording on your desktop. If you’ve got the processing power, you can even go HD – the tuner doesn’t care what resolution the signal is.
Most digital TV tuners work under Linux, but it’s safest and easiest to stick with a known, good model. I picked up my Leadtek DTV1000T card for about $80. It uses the Conexant CX2388 chipset, which uses the cx88_dvb driver module, but I didn’t even need to know that: Ubuntu, like all good distributions, found the card at boot and inserted the proper module automatically. If you use an unknown card with a similar chipset, you should be able to get it working, but you may have to load the driver manually.
Either way, if the driver has loaded successfully, you should have a ‘/dev/video0’ file, and a ‘/dev/dvb’ directory with various bits in it. The next step is to scan for channels with the ‘scan’ command, which is in the ‘dvb-utils’ package. It needs a base frequency file to work with, but these should be in the package as well – use the one that matches your region:
scan /usr/share/doc/dvb-utils/examples/scan/dvb-t/au-Melbourne >~/channels.conf
Once that’s finished, the channels.conf file should have a line for each channel detected. You can then feed these in to a video player like MPlayer: copy the channels.conf file in to your ~/.mplayer/ folder and open a channel, using the names listed in the file:
mplayer dvb://”SBS DIGITAL 1”
With any luck, SBS will be up and running for you. MPlayer works well in a pinch, but for a more complete digital TV experience, check out a front-end like Klear, which lets you play and record TV with ease.
Video conversion and DVD ripping
Linux has some great general-purpose video conversion tools, including MEncoder, FFMPEG and Transcode. You can rip straight from a DVD to a nice XviD-encoded AVI file with a single MEncoder command, but there are a lot of fiddly bits to learn before you can pull that off well. A better option is to use
dvd::rip, a very neat GUI frontend to the low-level conversion tools.
dvd::rip can be a hassle to install manually, because it depends on so many external tools to do the heavy lifting, but it’s mature enough that your distribution probably has packages – Ubuntu has one in the multiverse repository. It requires a little bit of setting up on the first run, but after that it’s very straightforward, with a series of tabs that you can click through step-by-step to configure the rip.
There are some other good special-purpose frontends like PSP Video Converter and Simple iPod Video Encoder as well, but I haven’t yet found a great general-purpose video encoding frontend. Basic usage of MEncoder from the command-line isn’t too tricky though, and again, most distributions will probably have it packaged.
Because MEncoder is based on MPlayer, it accepts just about anything as an input file, and it takes just a few options to select the basic encoding settings. Here we convert the input file to an AVI file with XviD video and MP3 audio:
mencoder input.mpg -ovc xvid -xvidencopts bitrate=800:autoaspect -oac mp3lame -lameopts cbr=128 -o output.avi
You can build on this base with extra video filters, using the ‘-vf’ option. For instance, you may want to resize the video, particularly if it’s widescreen – many widescreen videos have non-square pixels, and while the ‘autoaspect’ option above lets you record the aspect ratio in to the file, many players ignore it. It’s much safer to resize the video to a nice 16:9 resolution, like 640x360 pixels, using the ‘scale’ filter:
mencoder input.mpg -ovc xvid -xvidencopts bitrate=800 -oac mp3lame -lameopts cbr=128 -vf scale=640:360 -o output.avi
To improve video quality at the expense of processing time, you can tweak the XviD encoding options significantly. I find that the options ‘vhq=2:bvhq=1:chroma_opt:quant_type=mpeg’, added to the end of the ‘-xvidencopts’ section, work well. You can also enable two-pass encoding which, as the name suggests, encodes the file twice: the first works out how complex each bit of the video is to compress, and the second uses that information to adjust the bitrate as it goes. This saves data from simple sections and uses it to boost quality on the tricky bits. To enable this, add ‘pass=1’ to the above options on the first run, and ‘pass=2’ to the second.
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| Klear is a great digital TV recorder/player. |