Monday, July 17, 2006

HD DVD vs. Blu-ray (Pt. VI)

After I wrote HD DVD vs. Blu-ray (Pt. V), in which I discussed the audio capabilities of Blu-ray discs and players, I discovered this snippet at the Digital Bits website which suggests that the first Blu-ray disc titles have linear PCM 5.1 audio tracks (!):

Okay... a little bit of follow-up on my experience with Blu-ray disc and [the] Samsung BD-P1000 player. ... Let me just say that the PCM 5.1 uncompressed audio on these Blu-ray discs is absolutely spectacular. Smooth, rich, enveloping... these audio tracks are just really impressive. It's a lovely experience listening to these discs.

It doesn't say what other audio tracks, if any, there are on the first BDs. But linear PCM 5.1 is the gold standard of multichannel audio ... barring LPCM 7.1, that is. LPCM is uncompressed, so the entire soundtrack can be recovered by the player, with no compromises.

If LPCM 5.1 is in fact the standard audio format that most or all Blu-ray discs are going to be blessed with, that puts them one up on HD DVDs, which focus on lossily compressed Dolby Digital Plus encodings.

And let me emphasize again that the LPCM tracks on Blu-ray discs will play back at their very best over HDMI, with "PCM" selected in the player instead of "bitstream" — that is, if you also have an outboard HDMI receiver that accepts multichannel LPCM that way — or via the player's six analog-output RCA jacks.

I'd go so far as to speculate that uncompressed, multichannel, so-called linear PCM audio is actually the dark-horse form of audio in the incipient hi-def disc format wars. We've heard a fair amount about Dolby Digital Plus and DTS HD, two lossily compressed multichannel audio codecs these discs either use now or may incorporate in the future. And Dolby TrueHD and DTS HD Master codecs are set to afford us losslessly compressed multichannel sound.

But HD DVD players have to decode those and also standard Dolby Digital and DTS to linear PCM in order to deal with "advanced content" audio. All HD DVD discs available in this country so far feature that: a way, also called iHD, to allow interactive video and audio materials from the disc — mainly menus and their associated sounds — to function while a movie is playing.

Once multichannel audio from the disc is translated into LPCM and its various constituents are mixed together as needed, it has to be — by the first Toshiba HD DVD players to arrive on the market, the HD-XA1 and HD-A1, at least — re-encoded into standard DTS if it is to be shipped to an external receiver or processor in the form of a "bitstream." Re-encoding to standard DTS recompresses the signal. This is so whether the bitstream is sent out on HDMI or on the S/PDIF coaxial or optical digital outputs.

A better option is to send 5.1-channel analog audio from the player out to the receiver or processor — if it can accept it, that is. That involves no recompression.

Another equally good option is to send 5.1-channel linear PCM audio — i.e., uncompressed digital audio — from the player to the receiver or processor. This has to be done over HDMI. S/PDIF doesn't have enough bandwidth to handle it. That digital form of retransmission again involves no recompression.

But few receivers/processors today support it. Future receivers almost certainly will — particularly if they implement HDMI 1.3. The current HDMI standard, 1.1, is supposed to allow for multichannel PCM, but few of the HDMI-capable receivers now in existence actually support it.

Meanwhile, Blu-ray players and discs already support straight-through multichannel LPCM on input, internally, and on output — with no compression during disc authoring, no decoding by the player, no re-encoding in another format, no recompression. LPCM in fact looks to be the default audio format for Blu-ray discs and players ... which gives Blu-ray a small but possibly significant advantage over HD DVD.


After I wrote my prior post I also discovered this excellent article on the early HD DVD/Blu-ray experience at the website. You'll have to register (for free) to read it. It's author, Stephen Manes, likes the new formats' "video with six times the resolution [of standard DVD] improved audio and interactive features like pop-up menus, video commentary that can play along with the movie and the ability to bookmark favorite scenes. ... Watching the best [of the new discs] after viewing an old-fashioned DVD is like coming home with a new eyeglass prescription."

Yet he finds "
plenty of reasons to wait" to buy into either of the new formats. For one thing, "to see and hear every last bit of the newly revealed detail takes video and sound systems that most people don't have." Also: "For now, there are fewer than 200 hi-def discs available. And, as commentators enjoy ranting about, those discs are arriving in two utterly incompatible formats."

Manes says the broader intial support by movie studios and consumer electronics manufacturers for Blu-ray over HD DVD won't necessarily decide this format war. Why not? Sony's "
PlayStation 3, initially thought to be the Trojan horse that would bring Blu-ray into the home, turns out to be later and pricier than expected. And in the early going, HD-DVD has had some surprising short-term wins."

"For example," Manes says, "HD-DVD movies are coming out on 30-gigabyte dual-layer discs, while Blu-ray titles have been limited to 25-gigabyte single-layer platters with dual-layer versions dimly on the horizon. And early Blu-ray titles use old-fashioned [MPEG-2] compression that eats up disc space. HD-DVDs typically use newer, more efficient methods [VC-1, AVC] that cram far more stuff into the same space, with similar quality. Blu-ray discs can use those methods, but at the moment they don't."

So if Blu-ray has a slight advantage over HD DVD in terms of audio quality, the Blu-ray camp clearly goofed in not putting out its debut discs using two layers and efficient modern compression methods. It has thus for the moment squandered Blu-ray's nominal capacity advantage over HD DVD, which is why there are complaints that the first BDs boast few extras.

Those extras which are there are retreads from standard DVDs. Says Manes: "
But extras recorded in standard definition tend to look lousy. When the bonuses start getting shot in hi-def, the advantage should go to Blu-ray, with its potential for more room."

Manes also chafes at the fact that, unlike with HD DVD players, with
today's Blu-ray players the bookmarks you set "disappear the instant you open the tray."

Manes notes that HD DVD players can output only interlaced 1080i video, not progressive 1080p, as Blu-ray players can. "Though 1080i introduces some real but generally unnoticeable 'artifacts' that can slightly distort motion onscreen," he says, "1080p creates a different set of motion artifacts all its own."

I would differ with that last statement, as it applies to movies. If 1080p is output at 24 frames per second — the frame rate of film — or a multiple thereof it creates no motion artifacts. But if it's output from the player at 30 or 60 fps, it does. It then develops an irregular, stuttering cadence, due to the fact that the output frame rate is not a multiple of 24.

This is why 1080p TVs of the future will need to handle input frame rates of 24 and its multiples: 48 fps, 72 fps ... and even up to 120 fps, since that is the lowest common multiple of 24 and 30 or 60 (used for material shot directly to video).

To continue with Mr. Manes' discussion, though:

Another short-term Blu-ray advantage: better sound. Its uncompressed [linear PCM] audio tracks are said to sound much like high-end DVD-Audio or SACD discs — in other words, significantly better than what you currently get on DVD. I don't have the proper equipment to test that claim, but it's safe to say that to hear the difference, you'll need a system better than the typical home-theater-in-a-box. And HD-DVD discs with uncompressed audio are supposedly on the way.

That bolsters my own ideas, stated above and in earlier posts.

Manes lists various complaints about the first HD DVD and Blu-ray players — they're
fairly minor, but for some potential early adopters they could be deal breakers — then goes on to suggest that the new formats (and standard DVDs upconverted to 1,080 lines for playback) look best on TVs that handle 1080p input. Hi-def discs from the two formats, he says, do look "slightly better than hi-def movies I'd recorded on my cable DVR." They look especially good, he notes, using "Sony's astounding SXRD front-projector, aimed at a 100-inch Stewart Firehawk screen":

... if you want to keep your friends, invite them over to see this [he writes]. Watching movies by reflected light, the way they were intended to be seen, on a big screen that brings the theater experience to your home--only without dirty prints, smudges on the screen, uncomfortable seats or people in the row behind you on their cell phones--takes movies back to the way they were meant to be.

As with the audio capabilities, you clearly need the latest and greatest video gear to really appreciate HD DVD and Blu-ray.

There's also the worry, Manes says, that both camps might start including the dreaded Image Constraint Token on future discs. It would force players to stop outputting 1,080 lines of video resolution on any output but copy-protected HDMI. The video from disc would be down-rezzed to 540 lines or 480 lines on component video, so hi-def analog copies, re-digitized and then re-recorded, would become impossible.

Manes winds up by concluding:

... what might happen while nobody's looking is that downloads, not discs, become the winning format in hi-def. The Internet is getting faster. Cable and satellite companies are offering more high-capacity video recorders to let you capture their hi-def channels and over-the-air HD broadcasts that won't cost you an extra cent.

So if you really want to participate in the hi-def future, hold off on the disc player for now. Put the money into the kind of big 1920x1080 display that will showcase true HD.

Excellent advice, I'd say.

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