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January 9, 2011

Digital System

The biggest issue in recording Japanese digital terrestrial (as well as BS and CS, i.e. satellite) TV broadcast is its tight DRM (digital right management). Although broadcast reception itself is free (except NHK, the public broadcast service that collects monthly subscription fees but not on "pay-per-view" or other means), the digital contents are encrypted in a very tight way called "ARIB25." A single private company, B-CAS Systems Inc., controls the whole DRM, and it strictly prohibits decrypted clear test contents from passing general computer buses such as PCI and USB. Several major brands license from B-CAS and manufacture digital TV receiver add-ons, but the recorded content files are still encrypted with the individual PC-unique key so that the recorded contents can be viewed only on the PC that recorded them. It is not necessary to mention that all of these  officially licensed systems are for Windows only. This is a huge issue for systems like mine that are based on Linux and aim at freely transferring recorded contents.

There are a few possible solutions for recording digital broadcast:
  1. Receive and record analog signals converted by the cable TV feed with the existing analog system
  2. Set up a local digital-to-analog STB (set-top box) and use the existing analog system
  3. Develop a brand-new digital system
In order to help those who cannot immediately afford a new digital-compatible TV and to save still-usable analog TVs from being dumped and trashed, the government asked cable TV companies to continue to broadcast analog signals by locally converting digital contents to analog. Most major cable TV companies have promised to do so for 3 to 5 years after cease of aired analog TV signals. This saves and extends my system's life for 3 to 5 years without any changes or additional investments, but only 3 to 5 years. After the grace period ends, no analog signals at all.
Pixela PRODIA PRD-BT102-PA1, a sub-5,000 yen digital TV tuner STB distributed by AEON
Using a local STB is supposed to require only relatively minor modifications in TV-station selection to my current analog system, so it should have a relatively low technical barrier. One of the issues was the cost of such an STB, which was about 20,000 yen ($250US as of writing) or more per reception (my system allows two simultaneous receptions). The government encouraged the industry to produce sub-5,000 yen (below $60US as of writing) STBs for free distribution to households with financial hardships and for those who wanted to continue to use their existing analog TV sets with minimum investment. Though the industry was initially skeptical about such products because of their high manufacturing cost (est. about 4,000 yen), at least three major businesses responded with their minimally-featured STBs. At one point in mid-2010, I almost decided to go this way as it appeared most feasible and practical, and I purchased two such STBs (Pixela PRODIA PRD-BT102-PA1, distributed by the AEON supermarket chain) when I went to Japan for a family vacation. Other sub-5,000 yen tuners include the Buffalo DTV-S110 and Maspro DT630.

I, however, was reluctant to start a project to write additional software to control the STBs using IR remote sticks. Why? In addition to the technical difficulty in detecting whether the target STB's poewr is turned on or off (I never understand why such an STB needs to be turned off), writing software to control an STB with an IR emitter is one of the least exciting jobs. And the efforts and investment would reward nothing regarding to picture quality improvement except it would become ghost-less. Who would get excited to build a system to scan wallet-size pictures taken by a good digital SLR?

The all-digital solution is ideal only if the DRM issue is resolved. Quite a few talented people challenged this, and a few actually succeeded. One famous solution is Friio, a USB-base STB from a Taiwan-based business that accepts a B-CAS card and records digital broadcast in an unprotected and freely-transferable way. Others include a sort of radical hardware hacking called ”TS-Nuki" (TS抜き) or transport stream extraction. Both are supposed to work only with Windows, but not with Linux.

I knew that one person finally cracked the ARIB25 encryption system and published his work, i.e. Linux source code, to the open source community, but I was still skeptical about its practicality because there would be much more necessary software modules such as recording the TS (transport stream) and gathering EPG (electronic program guide) than just ARIB25 decryption. In the summer of 2010, my continuous net-surfing finally rewarded me to find an excellent blog site that thoroughly explains how to build a digital TV recording system in a plain language with practical examples. This definitely ignited me! Though the site provides only the information about how to get the necessary software modules that a tech-savvy person living in Japan will find useful for building his own system, but it never offers a turn-key solution or a one-command-for-all package, it was indeed a great help for me! I posted a few additional questions to the site, and the site owner was kind enough to provide all the necessary information. So, I decided to start a new project.

Proceed to Digital System Hardware.

4 comments:

  1. Hi,
    I also use a pt2, and I was wondering if you managed to broadcast live tv.
    I would like to watch tv from another computer in my house or over internet.
    but so far I could not find a program compatible with pt2...
    good luck with your project

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  2. quick questions. is this same thing with people who records the content to DVD recorder and send us in USA to view will not work because of DRM issues?

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  3. Probably yes. But I am not familiar with the DVD- (or BD-) recorded contents. So far my interest has been (and will be) around the broadcast TS (transport streams).

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  4. AsQ, PT2 is just a tuner, AFAIK, and it cannot broadcast contents.

    If you want to view recorded contents on another PC over a network, it's trivial. You can use file sharing or something similar.

    Again, I am not interested in viewing live TV in this project.

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