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[csimon]

1. If I choose bitstreaming, why are there options for HDMI, SPDIF and what do they do?  As I understood it, bitstreaming just outputs whatever was in the file without any processing.  Does HDMI mean uncompressed multichannel audio in discrete channels and SPDIF mean multichannel compressed audio into 2 channels?  If so, if HDMI is chosen, would MC "uncompress" a DD 5.1 soundtrack into discrete channels for output?

2. I have an .mkv file ripped from a music concert DVD and it has a DD 5.1 soundtrack, so presumaly that's 2 channels.  It will only play if I choose SPDIF as the bitstreaming format. If I choose HDMI, it says words to the effect of "cannot output 6ch but 2ch would work". This might be answered by the answer to the first question, but I would have thought that bitstreaming would just output whatever the original soundtrack was (DD 5.1 in 2 channels) without trying to convert to discrete channels.  Or...does it mean that my particular HDMI port (or the device connected to it) doesn't support discrete channels?

[Hendrik]

SPDIF bitstreaming only supports plain DD/DTS, while HDMI bitstreaming also supports DD+/DTS-HD/TrueHD, thats really the only distinction. Its only a "preset" for which codecs are enabled for bitstreaming, you can also use the custom mode and set them manually.

[csimon]

OK thanks, but then why does the video I mentioned above (sorry, it's mp4 not mkv) which has a DD 5.1 soundtrack (shown as 2 channels in the tags, encoding MP4 AAC) only play with SPDIF?  It should play with either HDMI or SPDIF as far as I can see but MC seems to think it's 6 channels if HDMI is chosen.

The file was compressed from the original MakeMKV ripped file to mp4 with RipBot264 - which showed the soundtrack as AC3 and I chose the 5.1 FHG AAC-LC 320kbps [cbr] profile to convert it with.  Might this have converted it to 6 channels, even though it still says 2 in MC's tags?

[AndrewFG]

AFAIK Spdif only supports 2 channels (stereo) whereas Hdmi supports anything from 2 channels up to 8 channels (aka 7.1)

[Hendrik]

I chose the 5.1 FHG AAC-LC 320kbps [cbr] profile to convert it with. 

Well, if you converted it to AAC, its no wonder it doesn't bitstream anymore. DD/DolbyDigital is AC3, AAC is something else entirely.

[csimon]

Why does it bitstream when SPDIF is chosen but not when HDMI is chosen?

Has it been converted to 6 channels in the file and SPDIF downconverts it to 2 channels, in which case why does MC says 2 channels? Or is it still 2 channels in the file, in which case why does the HDMI option think it's 6?

[EDIT: In the meantime I'm going to re-rip it and compress it into .mkv instead, as with mkv format RipBot264 gives an option for copying the audio stream whereas you can only choose AAC conversion for mp4).

[glynor]

Why does it bitstream when SPDIF is chosen but not when HDMI is chosen?

DSP > Output Format > Output Encoding is perhaps enabled.

In this case, if JRSS is also enabled, then MC will upconvert two-channel stereo to however many channels you have selected in the Channels drop-down, and then encode it as AC3 and send it down the SPDIF.

If you're using two zones to do the test, you might not have the same option enabled on the HDMI Zone.

[glynor]

You can easily check what is actually inside the file using MediaInfo.

Please look that up and be sure what is actually inside the file, or else we can't discuss it intelligently.

[glynor]

I'll also note, part of why I think we're confused is that you haven't been very clear.  For example, I'm not sure if you just made a typo here, but this sentence makes no sense:

2. I have an .mkv file ripped from a music concert DVD and it has a DD 5.1 soundtrack, so presumaly that's 2 channels.

You have a file ripped from a DD 5.1 DVD and it presumably has two channels?  Huh?

So... Assuming my guess of the re-encoding in MC's DSP isn't correct, then please just figure out what is actually inside the files you're using.  FWIW, RipBot doesn't allow AC3 in MP4 because, while it is (now, not originally) officially supported in the MP4 spec, many popular players don't.  Most notably, iDevices won't play AC3 tracks when using the built-in video players, and iTunes only supports AC3 passthrough (bitstreaming) and can't actually decode AC3.  That's pretty common among the rippers out there.  If they allow AC3 to be passed through to MP4, it is usually not one of the "default profiles" and you have to enable it manually.

Therefore, it is probably assumed if you're ripping to MP4 that you can't play back an AC3 track at all.  If you ripped that disc, and it converted it to AAC, it probably converted it to stereo.  But MediaInfo will tell you what is inside it, so just look.

MP4 does "officially" support AC3, but many of the most popular players do not.  I also believe (though it is hard to find good references now) that

[csimon]

DSP > Output Format > Output Encoding is perhaps enabled.

In this case, if JRSS is also enabled, then MC will upconvert two-channel stereo to however many channels you have selected in the Channels drop-down, and then encode it as AC3 and send it down the SPDIF.

If you're using two zones to do the test, you might not have the same option enabled on the HDMI Zone.

In this zone, that I've enabled for HDMI bitstreaming, there are no DSP options selected.

[csimon]

I'll also note, part of why I think we're confused is that you haven't been very clear.  For example, I'm not sure if you just made a typo here, but this sentence makes no sense:

2. I have an .mkv file ripped from a music concert DVD and it has a DD 5.1 soundtrack, so presumaly that's 2 channels.

You have a file ripped from a DD 5.1 DVD and it presumably has two channels?  Huh?

I thought that DD 5.1 was compressed multichannel audio delivered via 2 channels, but maybe I'm mixing that up with SPDIF. With MC displaying 2 channels in the tag info, that reinforced my belief.

Since I've re-ripped and converted it into mkv, it is indeed now in 6 channels AC3 and the HDMI bitstreaming options work as I expected them to work. However, going back to the original file, I've run MediaInfo on it and it shows for the audio stream:

English, 320Kbps, 48.0KHz, 6 channels /2 channels, AAC (LC)

Does that give you what you want to know?

Remember that I picked the "5.1 FHG AAC-LC 320kbps [cbr]" profile in RipBot264 but MC displayed 2 channels in the tag info. It played OK with the SPDIF bitstream option (presumbaly 2 channels) but when the HDMI option was chosen it said 6ch wouldn't work. Currently, in Windows Sound Devices, it says only 2 channels are supported on the HDMI port, I assume because the TV that's connected to it won't accept multichannel audio? So is this why I'm getting the 6ch error message from MC, but why does it think the file is 6 channels when it only says 2 in tag info? Has the AAC conversion stored both a 6ch and 2ch version of the soundtrack in the file?

[csimon]

More info from MediaInfo on playing around with the options:

Channel(s)                               : 2 channels
Channel(s)_Original                      : 6 channels
Channel positions                        : Front: L C R, Side: L R, LFE

[glynor]

I thought that DD 5.1 was compressed multichannel audio delivered via 2 channels, but maybe I'm mixing that up with SPDIF. With MC displaying 2 channels in the tag info, that reinforced my belief.

You're mixing it up with Dolby Pro Logic, which is something entirely different.

MC shows 6 channels whenever there are really six channels.

Please copy/paste the entire audio section (in Text View mode) of MediaInfo's scan of the file.

[csimon]

Entire audio section:

Audio
ID                                       : 2
Format                                   : AAC
Format/Info                              : Advanced Audio Codec
Format profile                           : LC
Codec ID                                 : 40
Duration                                 : 1h 44mn
Bit rate mode                            : Variable
Bit rate                                 : 320 Kbps
Maximum bit rate                         : 335 Kbps
Channel(s)                               : 2 channels
Channel(s)_Original                      : 6 channels
Channel positions                        : Front: L C R, Side: L R, LFE
Sampling rate                            : 48.0 KHz
Compression mode                         : Lossy
Stream size                              : 238 MiB (10%)
Language                                 : English
Encoded date                             : UTC 2014-07-24 22:21:05
Tagged date                              : UTC 2014-07-24 22:21:11

[glynor]

That's a 2-channel AAC audio track and cannot be bitstreamed.

If it is coming across to your receiver as Dolby Digital via anything, then something is converting it.  Either MC's DSP, or if you are using DirectSound playback mode, perhaps your sound card drivers.

[csimon]

The HDMI port is connected to the TV and the TV is then connected to the amp via optical. Therefore it could be the TV that's converting it.

However it did bitstream from MC using the SPDIF option, via WASAPI (not Direct Sound) and no DSP enabled.

It didn't bitstream when selecting the HDMI option, MC offered to change the output settings to 2ch.