Bitstream, passthrough, decode - so what's the diff?
#1
Hi
Following great success of my previous topic - and by that I meant I learned something new and valuable, I'm going to ask another basic question that I have problem to get answer for.

Remember that I'm asking all of this in context of Kodi and media players that are used to play...well...media with Kodi.

I can highlight three ways of making my sound system generate sound waves commonly known as audio:
  1. Bitstream
  2. Passthrough
  3. Decode
But I'm not sure if I understand them correctly and I'm missing some details about them. So here we go.

Ad 1. Bitstream - used when each bit of audio data is send to the receiver without altering it in any way. That means when something is encoded in TrueHD it should be delivered this way.
Ad 2. Passthrough - this one decompresses audio for further processing but the PCM signal can already be send to the receiver at this point. But what kind of signal this is? Analog or digital?
Ad 3. Decode - if the previous one uses digital passthrough then this one would convert digital to analog and send that signal to the receiver.

My goal is to find out not only if there are devices that support bitstream but also if I need bitstream at all. Because maybe passthrough will be enough? I've seen advanced settings in Kodi and they all says 'passthrough'. I didn't find even one mention about bitstream and Kodi. Is that mean Kodi doesn't support this kind of data transfer? Or maybe Kodi supports it and just there are no devices that supports it? It's important for me because I have AV Receiver that can work with most codecs so I would like it to take decoding part. Is there any differences between bitstream signal and digital passthrough in terms of quality? Or maybe there isn't' anything like digital passthrough?

Yeah...that's a lot of questions. But all of them arisen after reading forums looking for my perfect media player.
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#2
afaik Bitstream and Passthorugh ist the same and PCM is just a (lossless) way of Decode
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#3
Bitstream and passthrough are the exact same: The player just sends the audio to the receiver to devide.
Decode: Exactly as it sounds. The player itself decodes the audio and sends it to the receiver as uncompressed audio.
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#4
As others have said Bitstream and Passthrough are two different words for the same thing - the audio is passed on its compressed form (digitally compressed, not dynamic range compressed) to the amp for decoding in the amp rather than in the Kodi platform.
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#5
Ok...so if I have device that supports passthrough and in Kodi I'll check passthrough and capable receiver then I'll see correct audio type at ma AV Receiver? I mean if video has let's say TrueHD that I'll see Dolby TrueHD on AVR's display?
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#6
Yes that is what you are looking for, the compressed TrueHD Audio stream is being extracted from the movie file and passed through to your AVR which is then doing the TrueHD Audio decoding.

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#7
(2016-05-24, 10:03)Draghmar Wrote: Ok...so if I have device that supports passthrough and in Kodi I'll check passthrough and capable receiver then I'll see correct audio type at ma AV Receiver? I mean if video has let's say TrueHD that I'll see Dolby TrueHD on AVR's display?

Yes - if your Amp and Kodi platform both support those compressed audio formats in bitstream mode, then selecting passthrough in Kodi will simply pass the compressed stream straight through to your amp, with Kodi not processing it or altering it in any way. Your amp will decode the audio - and most amps will display a DD, DTS, DTS-HD Master Audio / High Resolution Audio, Dolby True HD, Dolby Digital Plus etc. indicator on their displays. (And Atmos + DTS:x now too)

If your Kodi platform or amp only support multichannel PCM and don't support bit streaming, then Kodi will decode DD, DTS, DTS-HD MA/HRA or Dolby True HD (but not Atmos or DTS:x and not sure about DD+) to multichannel PCM. In this situation you are sill getting lossless decoding (for DTS-HD MA and Dolby True HD, though DD/DTS/DD+/DTS-HD HRA are not lossless formats) and there should be no major quality difference, but your amp won't display a DTS-HD or Dolby True HD indicator (as it is being fed PCM)
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#8
Ok. I really appreciate your explanations. Smile So basically I have to stick to ODROID C2 with LibreELEC, WeTeK Play 2S and maybe Shield TV to get what I want.
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#9
ODroid C2 will bitstream DD, DTS and Dolby True HD. With DTS-HD MA/HRA you'll only get the DTS core. Currently there is no DTS-HD MA/HRA bitstreaming nor is there PCM multichannel for lossless decode.
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#10
Hm...I thought that that was only about 7.1 passthrough...I had to understand it in a wrong way then. Thanks for the tip. It's good somehow - at least my list have shortened a little so I have only WeTeK play 2S or maybe Shield TV to choose from. Smile
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#11
(2016-05-24, 23:24)Draghmar Wrote: Hm...I thought that that was only about 7.1 passthrough...I had to understand it in a wrong way then. Thanks for the tip. It's good somehow - at least my list have shortened a little so I have only WeTeK play 2S or maybe Shield TV to choose from. Smile

No. I think wrxtasy posted about 7.1 DTS-HD not bit streaming - and some took this to mean 5.1 DTS-HD would - when the reality is that no DTS-HD MA/HRA will bitstream - whether it is 2.0, 5.1 or 7.1. What I think wrxtasy was trying to emphasise was that if you played a 7.1 DTS-HD MA track on a C2, you'd get the DTS core, but it would be limited to 5.1 (as DTS doesn't carry 7.1 normally - and 6.1 is a bit odd)

However I think the 7.1 is confusing things. There are a LOT of 5.1 DTS-HD MA/HRA tracks, and with those you still only get the DTS core still (so a good quality lossy encode, but not a lossless or higher quality lossy version)

Hopefully the C2's PCM multichannel and DTS-HD MA modes will be unlocked soon. PCM multichannel is great for FLAC and AAC stuff - as well as older Blu-ray ISOs that had multichannel PCM tracks (which were the norm before DTS-HD and Dolby True HD mastering tools became available). The original Casino Royale release that came with our PS3 was PCM multichannel I think.
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#12
If you want to bitstream everything then get an intel box like a chromebox.
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#13
No...at least not until there will be full codec support in Intel CPUs and from what I've seen there isn't at the moment. We're waiting for Apollo Lake from what I remember. But thanks for suggestion. Smile
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#14
(2016-05-25, 22:35)nickr Wrote: If you want to bitstream everything then get an intel box like a chromebox.

Or a Shield ATV.

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#15
(2016-05-25, 23:19)Tinwarble Wrote:
(2016-05-25, 22:35)nickr Wrote: If you want to bitstream everything then get an intel box like a chromebox.

Or a Shield ATV.
+1
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