Bitrate of the Dolby Digital?

[aaronwt]

What is the bitrate of the Dolby Digital output? Also what is the bitrate of the DD+?
Are there any plans to have a box in the future with HDMI 1.3 so the DD+ can be bitstreamed to a receiver for DD+ decoding.

[RonV]

Re: Bitrate of the Dolby Digital?

The max bitrate of DD is 640 kbps.

On the HDMI 1.3 that is up to the VUDU folks. DD+ would be one reason to go to 1.3 but there is very little hardware in the field that support DD+.

[aaronwt]

Re: Bitrate of the Dolby Digital?

So the VUDU box re-encodes the DD+ to the max DD bitrate? Or is there a core DD stream like with DTS-HD?

[Hagen]

Re: Bitrate of the Dolby Digital?

Dolby defines the transcoding from DD+ to DD. The transcoding is always done to the highest bitrate supported by DD (i.e. 640kbit/s).

We are using DD+ because it gives us better audio quality at lower bitrates than DD. And all our content is encoded with DD+.

Hagen.

[Nded]

Re: Bitrate of the Dolby Digital?

Observation: AppleTV Footnote 3 on http://www.apple.com/appletv/specs.html says they are only providing "128-Kbps audio"

That's must be some good Koolaid....

[aaronwt]

Re: Bitrate of the Dolby Digital?

Dolby defines the transcoding from DD+ to DD. The transcoding is always done to the highest bitrate supported by DD (i.e. 640kbit/s).

We are using DD+ because it gives us better audio quality at lower bitrates than DD. And all our content is encoded with DD+.

Hagen.

Thanks!

[cachest]

Re: Bitrate of the Dolby Digital?

Hope I don't get flogged too much for opening up an old post, but I wanted to see if Hagen might provide a little more info on this topic.

According to the Dolby white-paper on DD+, the DD+ input into the converter can be anywhere from 32-448kbps. It notes that the DD output is always padded out to 640kbps irrespective of the input data rate. The white-paper goes on to essentially recommend 96kbps and 192kbps for stereo and 5.1-surround respectively, which would lead me to believe that Vudu's DD+ at least meets those minimums.

...so 640kbps DD != 640kbps DD+. According to Dolby, it would appear that it is at most 448kbps DD+. I wouldn't be surprised to learn that the DD+ from Vudu is less. I'm sure the aim is probably a happy median between 192 and 448 (best quality/size trade-off).

Hagen, can you confirm the above? Any chance you can share some actual audio data rates (say from a Vudu HD movie w/5.1)? - If possible, I also wanted to sneak in a question about the encodes. Do you guys get masters from the studio and then encode them yourselves or are you at the mercy of what they provide (i.e. studios do the encodes)?

Thanks!

[NA9D]

Re: Bitrate of the Dolby Digital?

If possible, I also wanted to sneak in a question about the encodes. Do you guys get masters from the studio and then encode them yourselves or are you at the mercy of what they provide (i.e. studios do the encodes)?

Thanks!

My understanding is that Vudu gets a master from the studios and encodes it themselves. The Vudu file format is H.264 but the encoding is proprietary. Vudu is at the mercy of the quality of the studio master.

[Hagen]

Re: Bitrate of the Dolby Digital?

We are using DD+ 128 kbit/s for stereo and 256 kbit/s for 5.1.

DD+ can go beyond 448 kbit/s. It supports bitrates of up to 6Mbit/s (one of the reasons why it's not supported via S/PDIF).

We are using Dolby encoding software (I don't think there are any other solutions out there anyway for DD+ encoding).

Most encodes are done in house but we also use external companies to do the encoding for us based on our specifications.

I hope that answers your questions,

Hagen.

[HeadHodge]

Re: Bitrate of the Dolby Digital?

I'm pretty ignorant on this topic, but my common sense tells me that sending video content is a 1000+ times more intense than audio (no matter what bitrate).

So, based on that premise, is it that big of deal to "technically" deliver the best audio available?

I've always been curious about that.

[Nded]

Re: Bitrate of the Dolby Digital?

I'm pretty ignorant on this topic, but my common sense tells me that sending video content is a 1000+ times more intense than audio (no matter what bitrate).

So, based on that premise, is it that big of deal to "technically" deliver the best audio available?

I've always been curious about that.

Actually, it can get quite complicated, and require much more sophisticated gear. For example, the Vudu output is "only" 5.1 channels, which some audiophiles would consider to be sub-par compared to 7.1 or even greater degrees of zone segmentation. Some special recordings could even call for multiple sub-woofer channels. Of course delivering the complicated signal is just the tip of the iceburg, compared to the gear you would need to reproduce the sound to such demanding specifications.

For the vast majority of movie viewers this is not an issue - they can not hear the difference, nor would they consider paying for it to happen.

[cachest]

Re: Bitrate of the Dolby Digital?

Thanks NA9D and Hagen! I appreciate you taking the time to satisfy my curiousity.


My answer to the question on video vs audio is the cliched "it depends".

If by "sending video content", you are talking about the amount of bandwidth and space required to handle the video portion of the movie, then the answer is yes, the video bandwidth and size will always dominate. Maybe I shouldn't say always... It would certainly be possible to encode a movie with an audio bitrate that exceeds the video bitrate, but you won't see anything like that from Hollywood.

If we talk about which is more difficult to encode (i.e. compress), then it gets a little less clear. The compression algorithms used today (for example, DD+ and H.264) are very advanced. The tools to do the compression are going to do things like make multiple passes across the data, and they will use mathematical algorithms and clever tricks along the way to get an end result. Scenes with lots of action, movement, bright-flashes of light, etc. are going to be more difficult for the video encoder to handle, whereas scenes without much going on are easier. The same holds true for audio. When there are lots of sharp, crisp transitions in the audio it is more difficult to compress than if there was no sound in the scene. Neither is black-magic, but both audio and video compression are technically impressive (at least to me).

I could post links with examples, but I think I've rambled on enough for one night. Let me know if you would like more info.

Thanks!

[NA9D]

Re: Bitrate of the Dolby Digital?

You are completely correct. The Vudu employe variable bit rate (VBR) to get the most efficient compression possible. This is the same as what DVDs use.

Compression theory is quite interesting. Back in 1988 I did a stint in Japan for their international phone company (a 2 month engineering student exchange program). I was working on a system that was designed to send images over a packet switched network between 2 CRTs. My task was to play with the compression algorithm to try to get the most efficient and quickest file size. Little did I know that this same technology would be in use just a few years later to send images over the web. I'm sure that the algorithms are far more complex than what I was working with back then but the concepts are still the same...

[Julien]

Re: Bitrate of the Dolby Digital?

We are using DD+ 128 kbit/s for stereo and 256 kbit/s for 5.1.

DD+ can go beyond 448 kbit/s. It supports bitrates of up to 6Mbit/s (one of the reasons why it's not supported via S/PDIF).

We are using Dolby encoding software (I don't think there are any other solutions out there anyway for DD+ encoding).

Most encodes are done in house but we also use external companies to do the encoding for us based on our specifications.

I hope that answers your questions,

Hagen.

Hagen,
Last night was my first night with VUDU and first time watching a VUDU film. I first watched the HDX promo trailer and the SQ was quite good (although it was all electronic). I then decided to watch an HD film not available in HDX. I chose Shine a Light since the lighting and fast action/edit cuts would be a tough test for the video encoder and of course the audio. The video passed with fling colors with almost no pixelation/micro blocking and minimal banding. The only real problem was resolution detail which is understandable given the <4Mbps data rate.

The REAL problem was the audio and for some reason I have always been very sensitive to perceptual coding artifacts. At some point (transmission stream?) the bit rate must have been compressed to less than 150Kbps. SQ was about on par to XM/Sirius and the perceptual coding artifacts were horrific. Pre echo and ringing were prevalent, collapsed sound stage with lots of high frequency roll off and a general "hurt your teeth" effect. I started the film a reference level but quickly lowered it by 3dB and the ear fatigue was almost unbearable.

Was there an audio encoding mistake with this film? Do all HD films have the same encoded data rate? Do HDX films have a higher audio encode rate?

[NA9D]

Re: Bitrate of the Dolby Digital?

Julien,

I don't have the ears you do and so have never had the experience you have had! But I can say that the audio on HDX films is noticeably better than the audio on HD and SD films.