Tuesday, December 02, 2008

It's Been Awhile... Problems Playing Blu-ray.

For those of you who may actually read this blog, I apologize for not writing anything since June. I'm still around and hope to start posting more frequently.

We haven't made much progress lately with our product development. There are a couple of big hurdles, which we don't have a lot of control over that have slowed us down.

One of the issues that we have to deal with is multichannel audio playback of Blu-ray movies. Our product should be a pretty good match for the HD audio codecs, like DTS-HD Master Audio and Dolby TrueHD. Both provide lossless encoding of up to 8 channels of audio with a bitdepth of 24 bit and up to 192 KHz sample rate. The highest resolution will probably be 24/96 most of the time and many titles might be 24/48. With such high resolution it seems a shame to play this quality of audio with just a basic audio/video receiver. I think you'd want really high quality DACs and powerful, low distortion amps to play back this HD audio in its full glory. That's one of the reasons we think our product is a good fit for HD audio. We plan to include the highest quality DACs and amplifiers.

So here's our problem. Since our product is meant to be connected to your HTPC and will perform the duties of your soundcard, it is dependent on the movie playback software for decoding the audio streams. Currently, the most popular software for Blu-ray playback is Cyberlink's PowerDVD Ultra, ArcSoft's TotalMedia Theater, Corel's WinDVD 9 and Nero's Nero 8 Ultimate. From what I understand, none of these programs will let you play DTS-HD Master Audio or Dolby TrueHD without downsampling, unless your hardware supports a protected audio path (PAP). Basically to play Blu-ray movies with AACS copy protection using an HTPC, the hardware must have a PAP to play the original HD audio if the bitdepth and sample rate are more than 16 bit and 48 KHz. Without PAP, the HD audio has to be downsampled to 16 bit/48 KHz as per the AACS specification. The basic audio path starts with the software player, which decodes the audio from either the encoded DTS-HD Master Audio or Dolby TrueHD into multichannel LPCM (linear pulse code modulated) data. Next, the LPCM is transmitted to the DACs, which convert the LPCM digital data into analog waveforms. Finally, the analog waveforms are amplified and output to your speakers. So, the reason for AACS and the PAP is to prevent people from getting the digital data and making perfect copies of the original HD audio. The critical part of the audio path that needs to be protected is between the software player's output of LPCM and the DACs. Unfortunately, there's no hardware standard for PAP that can be used with any hardware device. You have to develop your own proprietary hardware/driver solution and get each of the software players to support it. Unfortunately, there's no industry group working on a standard either. Maybe Microsoft will provide some support and guidance with Windows 7, but I haven't read anything that gives me hope. Actually, I'd be surprised if Microsoft came up with a good solution since it seems they're not too motivated to support Blu-ray in any way. So, to say the least, I'm a little pessimistic about PAP and HD audio playback with Blu-ray movies. There are some workarounds, but it's a PITA. You can use AnyDVD HD to decrypt the Blu-ray disc, then you split the audio and video into different files, convert the lossless HD audio track into a multichannel lossless audio format like WMA lossless or FLAC, and then recombine the audio and video into a MKV file and play it back with something like Media Player Classic. Like I said, it's a pain in the ass. You also lose all the extras.

The thing that really bugs me about this is all the encrypted formats used in Blu-ray have been cracked. So the pirates have no problems getting the unencryped stream from a Blu-ray disc. Legimate owners of Blu-ray discs can't play the full resolution HD audio, but pirates can still copy it. Hopefully, the current trend toward DRM free music will carry over into the movie industry and they'll relax the PAP requirements in the future. Maybe they'll be more open to this if Blu-ray player and disc sales don't increase during this holiday season.


  1. If I were you, I wouldn't hold my breath for those with the media rights to relax anything in respect of DRM on movies. More likely is that someone will make the decrypting route more efficient. For example, some pirates are offering AVCHD discs disguised as Blu-Ray - (they'd become more popular if they didn't pretend to be Blu-Rays). So these guys probably already have automated the steps.
    My money would be on Linux making it more into the mainstream in future so PAPs become an irrelevance....

  2. Yes, at least I follow your bog. :) I've been following your product development with much interest, but I've recently suffered an amp failure so my purchase plans have been moved up. I was hoping your product would be out by the time I did the next round of upgrades on my theater.