What to Do When Multi-Channel Audio Streaming Doesn’t Work


By Anthony Grimani January 9,2013


 
Anthony Grimani (agrimani@pmiltd.com) is
president of Performance Media Industries,
with offices in Novato and San Anselmo, CA.
Streaming video and video on demand (VOD) are quickly replacing Blu-ray, DVD, cable, and satellite as our clients’ preferred methods for acquiring program material. And, although there are several industry standards in place for verifying audio and video performance for legacy sources, VOD is an entirely different animal.

In the streaming world, there are many providers running different applications on myriad devices, including BD players, gaming consoles, smart TVs, and set-top boxes from Apple and Boxee. It’s easy to configure the hardware in a manner that seems correct–and may work properly for one application, such as BD playback– without checking every VOD application to make sure it works as expected. But it’s unwise to leave it at that. VOD providers are playing some very nasty tricks on us in the audio department. Most of them don’t even realize they’re doing it, but it’s the kind of thing that generates grumpy client texts during our off hours.

 
The majority of audio content today is produced in one of three channel configurations: two-channel (both stereo and surround-encoded), 5.1-channel, and 7.1-channel. The producer selects flags in the audio bitstream with the appropriate number of channels. It is then handed off to providers, who encode it for their various delivery formats (disc, cable, satellite, stream, download, etc.). Our source devices detect the flag and read the channel configuration. We typically set them to output that same channel configuration to the surround processor. Once in the surround processor, we can use an algorithm like Dolby ProLogic IIx to map the two, 5.1, or 7.1 channels to the number of speakers in the system, usually 7.1.
 
That’s actually a gross oversimplification of the process, but it gets the point across. If one step is mangled, the channel configuration out of the player may be wrong.
 

VOD Surround Sound Problems

I often encounter situations that go something like this: You configure the source device to output audio as described above: two-channel for two-channel, 5.1-channel for 5.1-channel, and 7.1-channel for 7.1-channel. You play a disc (assuming you’re still using a disc player), and everything’s great. You get Dolby TrueHD, DTS Master Audio, etc., with the correct number of channels. Then you load the VOD application. You play a title with two-channel audio and discover that the player is still sending a 7.1 stream.
 
After checking all the speakers, you determine that there aren’t really 7.1 channels of audio. It’s just two, and they’re coming out of the left and right speakers. The player may be sending a 7.1 stream, but only the left and right channels contain any audio; the others are silent or dark. Upon further inspection, you come to the horrible realization that the surround processor thinks it’s receiving a true 7.1 stream and has disabled ProLogic II decoding. You can’t map your two real channels to the center and surround speakers. You’ve got dialog coming out of the left and right speakers, no center to anchor the action to the screen, and no surrounds to add ambiance. In short, you’re back to the Hi-Fi days of the late 70s and early 80s before Dolby Surround. Your client has paid for this really massive, expensive 7.1 system, and all he’s getting is two-channel sound.
 
Frantically, you switch over to a title with 5.1 audio. It’s a little better. You have a center and surrounds; at least dialog isn’t coming from way off screen anymore. But wait—the surround processor still thinks it’s getting a 7.1 stream. You can’t use PLIIx to expand the 5.1 channels to the back speakers. Let the hair-pulling commence.

 

 
Streaming video and VOD (Video in Demand) are quickly becoming clients’ preferred methods for acquiring program material, but unfortunately surround sound doesn’t always work as advertised from these sources.
Why VOD Audio Can be Flaky

In this scenario I just described, there may be a problem with your hardware, but more likely the content provider’s app is to blame. Apps frequently decode, mix, re-encode or otherwise manage audio before it is sent to the hardware portion of the device for output. A lot of app writers either don’t understand how to manage audio inside their apps, or don’t know what the specific hardware platform needs in order to format audio correctly for the output jacks. It’s also possible, but less likely, that the audio content was flagged with the incorrect channel configuration by the mastering/authoring engineering, or encoded with the wrong channel configuration by the provider. Usually problems of this type will be limited to one or a small batch of titles. A problem with every title from a provider indicates a bad app.
 
When you encounter something like this, I strongly encourage you to troubleshoot it, and report your findings to the provider. You may have to wade through several levels of customer support before you get to someone who understands what you’re saying, but you can get results. In the past two years, I have reported numerous channel configuration problems to Netflix and VUDU that have been corrected in subsequent updates. (Netflix actually broke one app a second time and fixed it again.) I am currently working with VUDU on a similar issue with their app for the PlayStation 3. Both companies have expressed their appreciation to me for helping them identify and correct the problems.
  

The Work-Around Solution

Unfortunately, reporting problems won’t get you out of a short-term jam at your client’s house. You have to wire around the problem, and it’s not always easy. My advice is to use source devices and surround processors that have flexible input and output configurations. For example, you may need to use HDMI for multi-channel audio, but resort to analog for two-channel, so it can be processed with PLII. The source device must simultaneously output HDMI and analog audio, and the surround processor must pair the HDMI video input with either HDMI audio or analog audio. Odd as it may seem, this kind of functionality is not common to all source and processor products. Once the connections are in place, you must test them with content from every provider that the source device supports. This means getting accounts with Netflix, iTunes, VUDU, Amazon, etc., and buying titles you know are two-channel, 5.1-channel, 7.1-channel or whatever that provider offers. During calibration, log the player into your account and test all the options. Just remember to log back out, or the VOD police will come around asking why dozens of people are using your account.
 
Yes, this is extra work added to an already full plate. You may think it’s a small thing that doesn’t matter—something your client won’t notice—but you’d be wrong. I was.
 
A while back, I finished calibrating a great system and proudly brought the client in for a demo. I played him some two-channel music and 7.1-channel movie clips from his BD player and a couple of live events on satellite to demonstrate the nice 5.1 ambiance for sporting events. He loved it. I flew home and got off the plane to a text rant from him employing lots of CAPITAL LETTERS. As soon as I left, he apparently tossed aside all the great demo material, pulled up the Netflix app on his player, and started watching Hawaii Five-O. Not the new Hawaii Five-0 with Scott Caan and the guy from Lost. This was the original starring Jack Lord. It was one of this client’s favorite shows, and he wanted to see how it looked and sounded on his new system. Unfortunately, the show’s two-channel mix was being embedded in a 7.1 stream by the Netflix app and locked into the left and right speakers. Hawaii Five-O’s not going to sound fantastic no matter how you slice it, but nobody deserves what he had to put up with: dialog coming from the Left and Right speakers way off screen, comb filtering, poor intelligibility. We finally hooked him up around the digital bitstream, with some two-channel analog cables and got PLIIx running. It sounded a lot better, and he was happy again, but it taught me a lesson about these new VOD providers.
 
Since increasingly your clients are watching material that are downloaded or streamed from VOD sources, you’ve got to check every mode of operation to make sure they are left with a positive sound experience. That’s more work for you during the final phases of the system debugging, configuration, and calibration, and you should make sure to account for it in your project bids.

Chase Walton contributed to this column.

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