- 1 HDTV Help Pages
- 2 Understanding HDTV
- 3 Recording HDTV
- 4 Playing HDTV
- 5 Transcoding HDTV
HDTV Help Pages
Setting up MythTV to fully use HDTV can be rather complicated. There are different HDTV formats for North America and Europe. Parts of this information may apply to other countries that use HDTV as well.
HDTV (High Definition Television) is sent as stream of binary data encoded in the radio spectrum. A digital tuner works much like a modem extracting the original digital data. The digital TV data is sent as MPEG-2, so if you can get the raw data, the compression is already done for you.
HDTV comes in three flavors: Broadcast, Cable, and Satellite. The encoding for each is different, sometimes requiring different hardware.
Antenna HDTV broadcast
This is called OTA (Over-The-Air) ATSC. You can get a tuner card that will extract the raw transport stream for a given channel. Antenna Broadcasters sometimes include multiple subchannels, all of which are part of the same transport stream. In some areas, subchannels include encrypted pay channels.
HDTV on Cable
Its standard is called QAM ATSC. Many of the OTA Tuner cards like AirStar HD-5000 or PcHDTV work with Clear (unencrypted) QAM. It just takes a little bit more time and energy getting it to work.
HDTV and Satellite TV
All channels off of Satellite are digital but not all of them are in HDTV Format. Most are Encrypted but not all of them (For example LyngSat Free OTA).
There are other Methods of grabbing data from the above Sources. Fortunately, for cable and satellite some of the converter boxes include a firewire port where the raw MPEG data is sent. In theory, MythTV can record unencrypted channels from this port. At this time, this is something that a few people have experimented with, but it is not yet ready for general use.
Europe uses DVB (Digital Video Broadcasting) for HDTV and digital standard definition video.
DVB-C For Cable
DVB-T For Terrestrial (Antenna)
DVB-S For Satellite
As discussed above, OTA ATSC and Clear QAM ATSC HDTV can be recorded at this time.
Several cards are now available for HD capture in Linux. The pcHDTV HD-2000, pcHDTV HD-3000, Air2PC Technisat AirStar HD-5000, and ATI HDTV Wonder are just a few that have Linux drivers available. There is little reason to worry about the differences between the HD-2000 and HD-3000 cards, except that the HD-3000 is still being sold, while the HD-2000 and the Air2PC have been discontinued.
The CPU requirements are quite minimal for recording because it's simply a matter of copying the transport stream from the card to the hard drive. I believe that people have reported success with less than 1GHz processors. While Playback is a completely different Story.
Another popular option is Firewire capture of digital streams directly from a cable box. As with the ATSC tuners mentioned above, the CPU requirements for this capture method are minimal, as the backend machine is simply copying an MPEG video stream to disk.
The drivers are a bit temperamental; it can take some effort to get them to work correctly.
FIXME: Explain the different drivers, kernel versions, and such.
Most people use nVidia cards to play HDTV, although ATI cards are capable as well. The minimum recommended nVidia card is usually the FX 5200. I believe that this is the fastest fanless video card available. It can usually be found for under $50. The minimum recommended ATI card is the Radeon 9600, which is also fanless, found for about $60. Even if you are going to output an HD stream to an SD TV, over S-video or composite, you will still need the minimum recommended cards, as the full video stream still needs to be processed.
The CPU requirements for playing HDTV are significant. While XvMC support (nVidia only) offloads some of the work to the video card, most people have reported better results with just using Xv acceleration.
The actual minimum requirements are hard to pin down, as people have reported conflicting results. Relevant factors may include the bus speed, memory speed, CPU speed, kernel version, Linux distribution, and compiler version and optimizations. Compiling X and MythTV with a recent gcc and optimized for your exact CPU may provide an important boost, so you'll hear some people talk about the importance of running Gentoo Linux for the extra performance.
I have it working with an AMD 2500 CPU and Gentoo. If you are using an ATI card, use at least a Pentium 4 2.8 or equivalent.
FIXME: Discuss setting up MythTV, including adjusting the minimum signal strength.
HDTV recordings typically consume slightly under 9GB per hour. Unless you have tons of storage, this will restrict you to a fairly small number of recordings unless you transcode.
FIXME: I haven't figured out how to do this yet. The editor function works to set a cutlist, but there is no option to set up a transcoding profile specifically for HDTV recordings. I suspect that further development effort is required before MythTV can transcode HDTV. Several people have reported on the mailing lists methods of using external programs for transcoding.
FIXME: There should be a discussion of the alternatives for keeping the original sound stream. How much space does a full surround sound stream take per hour? If you don't have a surround sound setup, you might as well convert to stereo; is there a way to preserve the original stereo stream only?