This is a followup to a previous article, I hear there’s a problem with playing satellite audio…, but I will try to go into a bit more detail here.
When you watch TV from a terrestrial TV station using a regular TV antenna, and you are using an audio receiver that supports 5.1 audio, you will often hear full surround sound, particularly from the major network stations. But when you run a backend system such as TVHeadEnd, and use Kodi to watch live or recorded programs from free-to-air satellite channels, you may see both Kodi and your receiver indicate that you are only receiving stereo (2.0) audio. This might be expected on a station or network that carries primarily old shows from the days of black and white TV, but if you happen to come across a network feed channel, you might be surprised to see that you’re still only getting stereo audio. This can be especially confusing if your ears are telling you that you’re hearing 5.1 audio, but Kodi and your receiver’s display indicate otherwise (no, you’re not going crazy).
Without getting too much into technical details, the issue is that most TV stations that transmit full surround sound encode the audio using a consumer friendly format, typically Dolby Digital. In North America, the ATSC standards specify Dolby Digital as the audio codec. Some satellite channels also transmit their audio in Dolby Digital format. If they do, and if the audio is 5.1 surround sound, chances are that both Kodi and your audio receiver will recognize that it’s receiving 5.1 surround sound.
But network feeds are not intended for consumers; they are intended for television stations. And therefore, each network can (and often does) use its own format for sending audio signals. A typical DVB-S or DVB-S2 satellite transport stream will contain several packetized elementary streams that can contain video, data, and most important for this discussion, audio.
A common situation is to see several audio streams that contain pairs of channels. The important thing to note is that the network can define these channels any way it wants to. As long as their stations can retrieve the audio and get it on the air in a format that consumer television receivers understand, that’s all that matters to the company that’s uplinking the signals.
In many cases the uplinkers will put a pair of mp2 audio channels on the first audio stream. If those channels are encoded using Dolby Digital or Dolby Digital Plus format, then both Kodi and the receiver will generally indicate the true number of channels. However, there are other audio formats that are not intended for direct reception by end users, such as Dolby E, which is described as:
An audio encoding technology, Dolby E enables broadcasting and postproduction facilities to carry up to eight channels of sound over their existing stereo (two-channel) infrastructures.
Dolby E is not intended for reception by home viewers:
Unlike some other Dolby technologies, the Dolby E signal never reaches your home viewer. Rather, it’s decoded back to baseband audio just prior to the final transmission and then reencoded into the final audio format—Dolby Digital, for example, or Dolby Digital Plus™.
Now if a satellite feed uses Dolby E, or some other format not intended for reception by home viewers, in theory that audio (or at least the extra channels beyond basic stereo) can’t be heard by the home viewer. And Kodi, and perhaps your receiver, will tell you that you are receiving MP2, 2.0 audio. Kodi doesn’t know what the format really is, so it doesn’t display any indicator for it.
And, whoever programmed the display for your receiver probably thought that as a consumer, you’d never encounter a Dolby E signal, so there’s no display indication for it. BUT, and this is just speculation on my part, it’s quite possible that your receiver contains a decoder chip that can decode more formats that those that are listed in the receiver’s user manual. So if it has a Dolby decoder chip and sees a Dolby E signal, it just might decode it, without changing the receiver’s display to indicate that it is doing so. Thus, if you are lucky, you might hear the surround sound, even though there’s no indication on your receiver’s display about what format it’s actually receiving. You might have to play with the audio settings on your receiver to make this happen (see the end of the previous article, I hear there’s a problem with playing satellite audio…).
I understand there’s another multichannel format called SMPTE 302M (s302m) that might appear on the first audio stream. I don’t believe that any consumer grade equipment can decode that, and Kodi seems to be smart enough to realize that there’s nothing usable where, so it skips to the first non-s302m stream. I may be wrong about that, but available information on that format is rather sparse unless you want to pay $50 to get SMPTE’s technical documentation, which I don’t.
The bottom line is that if the uplinker is encoding their multichannel audio using a format that intended for reception by broadcasters and not by consumers, Kodi probably doesn’t know how to deal with it. But if you have enabled passthrough audio in Kodi, your receiver might be able to decode it. Otherwise, you’ll probably only hear stereo audio (if you’re lucky), unless you’re trying to watch the network that sends all the channels as discrete audio.
And if you use a standalone satellite receiver rather than a backend system, you’re kind of at the mercy of the manufacturer. If the manufacturer spent the money to license the Dolby technology and has included an actual Dolby decoder chip, then you stand a far better chance of getting the surround sound than if the manufacturer was trying to build the receiver as cheaply as possible, and used no licensed decoder. But if the satellite receiver can pass the received audio stream to an AV receiver via HDMI or S/PDIF, then it’s possible the receiver might still be able to decode it, assuming it can decode Dolby audio.