Feature Request... Retain TrueHD 'AC3 Core'

[liquidskin76]

Hey Mike,

You said MakeMKV just copies the TrueHD track as is. I'll run another test using a MakeMKV mkv containing ONLY the TrueHD track and see if i get TrueHD over HDMI and AC3 over optical. It maybe that i'm mistaken, and the TrueHD track produced by MakeMKV does keep the AC3 core.

I'm sure i've done this test before however i think i'm starting to think i'm losing my mind!

Thanks

Ok, so i tested this...

MakeMKV mkv containing only vid and TrueHD. Can decode TrueHD or bitstream TrueHD. Crashes mpc-hc if i disable TrueHD decoding/bitstreaming, so no AC3 core embedded within the TrueHD track.

Using the exact same backup, i create a m2ts (with tsmuxer) using the same vid and TrueHD file. I can decode TrueHD, bitstream TrueHD, and if i disable TrueHD decoding/bitstreaming, i can bitstream AC3. That my friends is the embedded AC3 core file being used!!

As my original feature requested asked was... can the embedded AC3 core be retained within the TrueHD file when it's muxed to MKV by MakeMKV? Exactly like TrueHD/AC3 core is in a m2ts file on a blu-ray disc.

I'm not trying not to be a pain here... just want to make MakeMKV even better! There is a valid call and practical use for this feature!!

Thanks

[mrbass]

AC3 your are "seeing" is simply metadata telling it to downmix within the TrueHD stream. There is no AC3 core like you say although technically an AC3 track could be "carried independently" (NOT WITHIN TRUEHD stream). There simply isn't a need as all TrueHD receivers are capable of downmixing to 5.1 or 2.1. Although your saying you disabled TRUEHD decoding it's still just reading the metadata to downmix it. Just like on HD media player if you disable digital output and choose stereo it is STILL reading the digital DTS audio and downmixing it to stereo. Probably bad choice of terms being used by the programs.

Here's a few snippets from the technical PDF paper
http://www.dolby.com/uploadedFiles/Asse ... _Final.pdf

Channel Extensions, Downmixing, and Dolby TrueHD
One channel extension technique is the method by which MLP Lossless, Dolby TrueHD, and MPEG-2 LII deliver compatible downmixes for soundtracks with expanded channels. In these codecs, a 7.1-channel soundtrack is first downmixed to create a 5.1 mix...

If a listener selects a 5.1 presentation, the decoder reconstructs it from the
two-channel downmix plus the 3.1-channel extension A substream by means of rematrixing.

An A/V receiver with Dolby Digital decoding that has only a coaxial or optical digital audio input needs only a Blu-ray Disc player with a Dolby Digital Compatible Output that provides a compatible Dolby Digital bitstream from its internal mixer.

Due to the substream structure of Dolby TrueHD, a single Dolby TrueHD program can be used to deliver a two-, six-, or eight-channel presentation, each with precise control over the presentation as defined by the content producer. This means that an HD player needs to decode only the number of channels it can output, thus enabling more economical DSP decoder designs.

It should be noted that it is also possible for the two- and 5.1-channel presentations to be carried independently if it is important to avoid downmixing due to artistic reasons. In this case, however, the bit rate will increase due to the carriage of additional channels.

[liquidskin76]

AC3 your are "seeing" is simply metadata telling it to downmix within the TrueHD stream. There is no AC3 core like you say although technically an AC3 track could be "carried independently" (NOT WITHIN TRUEHD stream). There simply isn't a need as all TrueHD receivers are capable of downmixing to 5.1 or 2.1. Although your saying you disabled TRUEHD decoding it's still just reading the metadata to downmix it. Just like on HD media player if you disable digital output and choose stereo it is STILL reading the digital DTS audio and downmixing it to stereo. Probably bad choice of terms being used by the programs.

Here's a few snippets from the technical PDF paper
http://www.dolby.com/uploadedFiles/Asse ... _Final.pdf

Channel Extensions, Downmixing, and Dolby TrueHD
One channel extension technique is the method by which MLP Lossless, Dolby TrueHD, and MPEG-2 LII deliver compatible downmixes for soundtracks with expanded channels. In these codecs, a 7.1-channel soundtrack is first downmixed to create a 5.1 mix...

If a listener selects a 5.1 presentation, the decoder reconstructs it from the
two-channel downmix plus the 3.1-channel extension A substream by means of rematrixing.

An A/V receiver with Dolby Digital decoding that has only a coaxial or optical digital audio input needs only a Blu-ray Disc player with a Dolby Digital Compatible Output that provides a compatible Dolby Digital bitstream from its internal mixer.

Due to the substream structure of Dolby TrueHD, a single Dolby TrueHD program can be used to deliver a two-, six-, or eight-channel presentation, each with precise control over the presentation as defined by the content producer. This means that an HD player needs to decode only the number of channels it can output, thus enabling more economical DSP decoder designs.

It should be noted that it is also possible for the two- and 5.1-channel presentations to be carried independently if it is important to avoid downmixing due to artistic reasons. In this case, however, the bit rate will increase due to the carriage of additional channels.

Have just been looking through the official TrueHD spec, before you posted. I understand now... so no separate ac3 file, just metadata telling the player/software how to downconvert.

Ok, so let me revise my original request... can MakeMKV keep this metadata so a software player can downconvert a truehd track to ac3!!??

[SamuriHL]

Have just been looking through the official TrueHD spec, before you posted. I understand now... so no separate ac3 file, just metadata telling the player/software how to downconvert.

Ok, so let me revise my original request... can MakeMKV keep this metadata so a software player can downconvert a truehd track to ac3!!??

This has been quite educational.

[liquidskin76]

For me to! I was on the right track in that there is something that enables AC3 bitstreaming from a TrueHD file, just thought it was a core!

Software decoders like ffdshow must use the metadata then to downmix the TrueHD to AC3, as when playing an m2ts containing only TrueHD, i can get ffdshow to bitstream AC3 by disabling TrueHD decoding/bitstreaming.

The revised request therefore is can MakeMKV keep this metadata so software decoders like ffdshow output mkv truehd the same as m2ts truehd (downconvert to AC3)?

Thanks!!

[SamuriHL]

Seems reasonable to me.

[liquidskin76]

In the end, what i'm trying to figure out is why (using ffdshow for instance) i can bitstream AC3 from a TrueHD file within an m2ts container, but can't bitstream AC3 from a TrueHD file within an mkv container (created with either MakeMKV or MKVMerge)?

I know mkv's created with the new SMM muxer (over at doom9) can retain the same behaviour as an m2ts file, so why can't MakeMKV and MKVMerge? I'm guessing they discard some metadata?

[liquidskin76]

Hi Mike,

Check out madshi's (author of eac3to) and my last comment over at the doom9 thread...

http://forum.doom9.org/showthread.php?p ... ost1415254

Is this correct of makemkv (regarding following mkv spec)?

Thanks

[mike admin]

His comment is correct, but incomplete. On blu-ray disc an audio track contains both TrueHD and AC3. Mpeg transport stream is the only format that can have multiple streams per logical track. In Mpeg program stream (HD-DVD) or multiplexed elementary streams (MKV) one track equals one stream. MakeMKV creates two streams out of two streams which translates to two MKV tracks out of a single M2TS track. All data is preserved as-is.

[liquidskin76]

Thanks for the info Mike. Is that a physical limitation of mkv (regarding one stream per track), or a spec limitation?

Just wondering how come the new smm muxer on test over at doom9 retains the 2 streams per one track in the mkv files it creates.

Thanks again.

[robinsj]

I am really unsure what you are requesting here, because I have the exact setup you describe. I have 2 HTPCS both running XBMC. One uses hdmi out to a receiver that fully supports DTS-HD and TrueHD. The other is hooked up to a receiver via Optical/Toslink. The one with HDMI to the receiver plays everything with the DTS-HD and TrueHD lighting up the receiver. The other plays everything just fine too, and doesn't just play 2 channel audio.

The one that is connected via HDMI, I have setup in ffdshow audio configuration, in the output section, I have everything checked under the Pass-through (S/PDIF, HDMI) section. Then the other one with just the optical hookup, I only selected everything but truehd, and dts-hd. Everything plays back fine in 5.1 audio, and I don't keep two audio tracks in the truehd ones, just the truehd track.

What problem are you having?

[SamuriHL]

Oh for crying out loud. I'll put this as simply as possible....

He (and I wouldn't mind either for that matter) wants a TrueHD+AC3 track where the AC3 stream is interleaved with the TrueHD track. They are separate, but, they are interleaved. MakeMKV (and mkvmerge, too) only output a TrueHD track with no interleaved AC3 track. That's ALL that's being asked for. If you remove the AC3 interleaved track, tsMuxer no longer recognizes the TrueHD track.

[liquidskin76]

I am really unsure what you are requesting here, because I have the exact setup you describe. I have 2 HTPCS both running XBMC. One uses hdmi out to a receiver that fully supports DTS-HD and TrueHD. The other is hooked up to a receiver via Optical/Toslink. The one with HDMI to the receiver plays everything with the DTS-HD and TrueHD lighting up the receiver. The other plays everything just fine too, and doesn't just play 2 channel audio.

The one that is connected via HDMI, I have setup in ffdshow audio configuration, in the output section, I have everything checked under the Pass-through (S/PDIF, HDMI) section. Then the other one with just the optical hookup, I only selected everything but truehd, and dts-hd. Everything plays back fine in 5.1 audio, and I don't keep two audio tracks in the truehd ones, just the truehd track.

What problem are you having?

You won't be getting Dolby Digital 5.1 (as there's no ac3 to use), and you won't be getting uncompressed lpcm (as spdif/optical cannot handle the bandwidth).

I expect your receiver is taking the 2 channel and outputting as Dolby Prologic, Neural-THX, or something similar... fake 5.1 in other words!!!

[Viper]

Is there any plans to implement this, as it's the only thing keeping from using this otherwise great piece of software?

Thanks!

[mike admin]

Implement what exactly?