Sunday, June 05, 2005

Making Hi-Def Archival Copies

In Motorola DCT6412 HD DVR Cable Box I talked about the high-defintion cable box-cum-DVR Comcast supplies to its customers here in Baltimore County, Marlyand. One thing I didn't mention is that it sports a FireWire connector. That means it possibly can be used to export copies of digital TV programs!

I got the idea from a letter in the January/February 2005 The Perfect Vision magazine (p. 10; not available online). Reader Chris Teague writes that he (she?) archives HD material from a similar Motorola box to a D-VHS videocassette recorder.

An item on p. 16 of the March/April issue also mentions using FireWire to copy HD and other digital TV from a Sony cable box to D-VHS, and also to an external RCA hard-drive recorder.

What's going on here? Isn't that sort of thing supposed to be impossible?

Not, apparently, with FireWire. FireWire is a type of digital interface which can transport digital video, along with digital audio, from one device such as a cable box to another such as a D-VHS recorder. It's also used to connect PCs and Macs for transmitting data to/from peripherals. Special FireWire connections allow home movies to be copied from camcorders to PCs for editing. Other names for FireWire include IEEE 1394, i.LINK, and DTVLink.

FireWire (FW) differs from Digital Video Interface (DVI). FW uses different cables and connectors than DVI. FW carries only digitally compressed video and audio, while DVI carries only uncompressed digital video, and no audio. FW is two-way and its devices can be elaborately networked, while DVI is one-way and cannot.

Both DVI and FW are copy-protected. Each has its own protection scheme, HDCP for DVI and DTCP or "5C" (because five companies designed it) for FW. The two schemes have certain features in common. Basically, in either scheme, when a digital video stream is to be sent from a source device to a receiving device, both devices have to prove their bona fides as authorized units that are guaranteed by their manufacturers to play by the rules.

But FW's 5C copy-protection scheme adds "copy control" to the protection used for DVI. DVI's uncompressed digital video uses data rates too high to be copied by any consumer device, so copy control is a non-issue. But D-VHS recorders and certain other types of devices can record the compressed video (and audio) streams associated with FireWire.

So the FW source device plants a digital "flag" in the output stream, based on a similar flag it finds in the content it is outputting.

Content providers of over-the-air digital TV must, by law, flag their content "copy freely" — even when it comes to you courtesy of a cable system or satellite.

Pay-per-view and video-on-demand content is flagged "copy never." (This may be why my Motorola box can't record this content.) "Copy never" content can be viewed over a FireWire connection, but not recorded.

In between these extremes, "linear" (i.e., not user-selected) content on premium channels such as HBO bears a "copy once" or "copy one generation" flag. That lets you make an archival copy. The copy itself is marked "no more copies," so it cannot be duplicated.

Supposedly, the 5C standard does make provision for a "no more copies" archival copy to be moved — that is, copied to another recording device, with the original recording then being erased or deleted. But as far as I know, the "move" function remains dormant in all current 5C-compliant devices. (See the January/February 2005 issue of The Perfect Vision, pp. 53-54, for a bit more on this.)

My question is, accordingly, can I even make archival copies of hi-def movies airing on HBO and other premium channels? Very likely the answer is yes, with this proviso: I doubt I can copy the version recorded on the DVR.

That is, I imagine that with a FireWire-connected device I can externally record "copy once" content as it is being transmitted. But I assume that, as it is recorded on the DVR, it's flagged "no more copies."

But that assumption is subject to doubt. Here is a thread on the AVS Forum in which a poster claims that, by rights, "recording to the Hard Drive of the [Motorola 6412] STB does NOT count" against the "copy once" flag. True, the poster was in fact unable to copy HBO-type material to his D-VHS recorder, suggesting he may have been wrong. Moreover, he failed to follow up after being asked whether the same problem cropped up with realtime HD content, or with presumably un-flagged material on INHD. So in my mind the whole issue remains unresolved, and I can as yet find no further information on the Web that would resolve it.

Another possibility is to record the cable box's realtime and/or recorded HD or SD content as sent via FireWire to a computer. I have a Mac, and there is information about how to do this sort of thing here. Also here. And also here.

One of the caveats here is that the content you want to record on your computer cannot be encrypted or scrambled. Encryption is separate and distinct from copy-control flagging. It scrambles the digital TV data in a way that (presumably) only an authorized receiving device can cope with. A Mac or PC is not an authorized device that knows how to decrypt scrambled cable channels.

Another caveat for us Mac'ers is that Mac OS version 10.3.x (Panther) must be used. No earlier versions will work ... and it's not absolutely clear that the latest-and-greatest version, 10.4.x Tiger, works either.

I have two Macs, an iMac running Panther and the other, a now-ancient PowerBook laptop, running 10.2 Jaguar. It's so sluggish, I'm not sure I want to burden it with Panther (or Tiger). It's processor is too slow for importing HD video, and it's hard drive too small.

The iMac would probably work ... if I had a lot more free disk space. But it's on the top floor and the Motorola is on the ground floor. Connecting it (or lugging it) would be a hassle.

If I were to do this, I'd clearly need to replace the old PowerBook with a new one with a lot of horsepower and disk space.

But I don't really fancy the "computer option." At best, it would be true HD in name only, since I know of no way to save any significant amount of HD video as such without chewing up however much disk space I have. I figure maybe 5-to-10 GB per hour of HD material would be needed.

I could cut that perhaps by a factor of 1/10 (I'm guessing) if I used DivX compression. DivX is how most video content shared illegally over the Web is compressed. But that would compromise the video quality, so what's the point?

No, the way I'd really like to go would be to use something like a D-VHS recorder ... but disk-based.

Using DVD-like, removable media.

That I could keep forever.

Right now, that's not possible. In a few months, though, high-definition DVDs will arrive — including recordable versions thereof.

There are actually some hi-def DVD formats here today, but the ones people are waiting for use a blue laser, not red. Red lasers can't focus their beam tightly enough to cram truly vast amounts of data on a single disc. Blue lasers can.

Trouble is, there are likely to be two competing blue-laser formats, HD DVD and Blu-Ray. Each has a roster of important companies in its stable, and neither can be played in the other format's players. Can you say "format war"?

There are some indications the HD DVD and Blu-Ray camps may hammer out a compromise to avoid a war. We'll probably know very soon.

If some version of prerecorded blue-laser HD disc captures consumers' hearts in the next year or two, then recordable versions thereof ought to serve nicely as hi-def archival media. One can at least hope a FireWire-capable blue-laser recorder/player, suitably authorized for the purpose of archiving HDTV, will come to market not long after the blue-laser format is (formats are?) introduced.

I'll keep my fingers crossed.

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