The DIY HTPC Dilemma

A comment by Steve on a recent blog post brought up a commonly asked question:

Any plans to include an input card with component RGB or Y’PbPr? How about HDMI?

Well, Steve, to be short:

No, because I can’t.

Let’s start off with a brief history lesson on TV and a few definitions.

• Interlaced
  When displaying an image, older TVs will used an Interlace formula. This is where the odd lines are first all transmitted, then the even lines. This reduces bandwidth while also creating a smoother image.
• Progressive Scan
  When an image is to be displayed, the image is transmitted from top left to bottom right. This requires a high bandwidth to maintain motion smoothness but results in better picture quality.
• NTSC TV (480i)
  The original 4:3 TV. 640 x 480 pixels, interlaced. It’s what you’ve been watching since cable has been around. Uses Composite (Yellow) and S-Video cables to connect to your TV. 480i means 480 horizontal lines in an interlaced format.
• Progressive Scan (480p)
  Popularized with the DVD Player. This utilized progressive scan to produce better picture quality. To display this image Y’PbPr cables need to be used since Composite and S-Video can only handle 480i.
• ATSC HDTV (720p, 1080i, 1080p)
  HDTV features both interlaced and progressive scan formats in a variety of resolutions. In addition to higher resolutions, ATSC TV made 16:9 (widescreen) as the default resolution.
• Digital Connectors
  To display these higher resolutions with better picture quality an all digital interface was created (HDMI) which carries both digital video and digital audio. DVI is also used as a digital video connector.

The Problem
With the higher resolution and the increased screen real estate, ATSC takes more than 6x the bandwidth of NTSC TV. To combat the higher bandwidth requirement, ATSC is transmitted in a compressed MPEG-2 format, which is then decompressed by the receiver, and then finally displayed on the TV.

Decompression takes far less processing power than compression. So, to answer Steve’s question, because of the extremely high bandwidth there are no consumer-level products that let you take an uncompressed ATSC signal and process it.

Naturally, we would want to take the stream while it is in the compressed MPEG-2 format, which is what we do. These streams come over a cable line (QAM) or through an antenna (OTA). Problem is, cable companies encrypt all their premium pay channels before transmitting them which prevents us from accessing them.

What options do we have left?
Well, there’s this thing called CableCard. Basically, it has the codes to decrypt the MPEG-2 streams then use them. The problem is that to get a lisence to build CableCard hardware, the Cable companies have to approve of it. There has been only one CableCard enabled tuner produced thus far - and it took both ATI and AMD to produce it. It’s only available to certified OEM system builders, requires a specific chip on the motherboard which Windows Vista then places a DRM on all files recorded to lock it ONLY to the system it was recorded on. Sounds like fun.

Basically the consumers have to wait until more options come out. In the mean time, the FCC has helped us out and required that the cable companies transmit all local broadcast channels (ABC, NBC, etc) unencrypted which allows us to start accessing some HD content. If you want to help the situation, side with the EFF - one of the few parties actively fighting for your rights.

–Andrew