Losslessly edit UHD 4K Blu-ray w/ Dolby TrueHD?

[ogrgkyle]

I have a Blu-ray with 4K UHD HEVC video and Dolby TrueHD 7.1 audio ripped to MKV with MakeMKV. I want to edit it and "smart render" it back to MKV.

The only software I have found to edit the 4K UHD HEVC video is TMPGEnc MPEG Smart Renderer 6. However, this converts 7.1 audio to 5.1.

The only software I have found to edit the Dolby TrueHD 7.1 audio is VideoReDo TVSuite 6. It saves the audio as an 8-channel PCM track. However, this does not support UHD HEVC.

I want a solution for losslessly editing this file and only re-encoding the cut areas. My only solution so far is to edit the video in TMPGEnc and edit the audio in VideoReDo, then mux the tracks together with MKVToolNix. And I don't know enough about audio to know if VideoReDo's PCM output is the same as the original Dolby TrueHD track.

So how can I edit this MKV losslessly? I'm open to paid software or using multiple tools, command line, ffmpeg, avisynth, etc. I'm familiar with these tools, but maybe you can help me find the solution. Please let me know if there's any way. Thanks.

[Luke M]

Is this Atmos? Editing Atmos is pretty much impossible. So just convert it to 7.1 PCM or whatever lossless 7.1 format makes your editor happy.

[ogrgkyle]

Yes, it's Atmos. I don't care if the final product is PCM, if the tracks' 7.1 configuration is exactly the same. Is there a way to convert this to 7.1 PCM via ffmpeg or another tool? If it helps, I want to edit the audio in Vegas Pro and export as 7.1 PCM.

[usually_quiet]

I have a Blu-ray with 4K UHD HEVC video and Dolby TrueHD 7.1 audio ripped to MKV with MakeMKV. I want to edit it and "smart render" it back to MKV.

The only software I have found to edit the 4K UHD HEVC video is TMPGEnc MPEG Smart Renderer 6. However, this converts 7.1 audio to 5.1.

The only software I have found to edit the Dolby TrueHD 7.1 audio is VideoReDo TVSuite 6. It saves the audio as an 8-channel PCM track. However, this does not support UHD HEVC.

I want a solution for losslessly editing this file and only re-encoding the cut areas. My only solution so far is to edit the video in TMPGEnc and edit the audio in VideoReDo, then mux the tracks together with MKVToolNix. And I don't know enough about audio to know if VideoReDo's PCM output is the same as the original Dolby TrueHD track.

So how can I edit this MKV losslessly? I'm open to paid software or using multiple tools, command line, ffmpeg, avisynth, etc. I'm familiar with these tools, but maybe you can help me find the solution. Please let me know if there's any way. Thanks.

Since Dolby tightly restricts access to their TrueHD encoders and to information about their TrueHD format, software capable of cutting and joining TrueHD audio and exporting it as TrueHD audio probably doesn't exist, particularly software that consumers can obtain.

The conversion to 8-channel LPCM should be lossless if your MKV file contains Dolby TrueHD without Atmos object data. if your MKV file contains Dolby TrueHD with Atmos object data then it won't be lossless because the Atmos object data won't be preserved.

VideoReDo TV Suite is supposed to have the ability to edit 4K HEVC. The difference between VideoReDo TV Suite v6 and is that TMPGEnc MPEG Smart Renderer 6 can edit 4K HEVC with HDR-10 and VideoReDo TV Suite v6 can't handle HDR-10 yet.

[ogrgkyle]

I ripped a 4K Blu-ray using MakeMKV. How can I tell if it has Atmos object data? What in the world is Atmos object data?

Yes, I opened it in VideoReDo and exported it to MKV. (I know this software doesn't support 10-bit, but I wanted to test the audio.) The audio was exported as 7.1 PCM. Do you expect this to be equal to the original audio? Can I edit this PCM track in Vegas Pro and export as PCM, and re-mux it back into the MKV?

And as for video, yes, I must edit the 4K 10-bit HEVC in TMPGEnc. This will have to be a two-step process: edit the audio losslessly in Vegas Pro (if possible) and edit the video in TMPGEnc, and mux the streams together. Unless you have a better suggestion.

[usually_quiet]

I ripped a 4K Blu-ray using MakeMKV. How can I tell if it has Atmos object data? What in the world is Atmos object data?

You already wrote that the audio that you ripped was Dolby Atmos. For a short explanation of how Atmos is implemented on UHD Blu-ray and what Atmos object data does see https://www.soundandvision.com/content/how-do-dolby-truehd-and-dolby-atmos-differ

At that link, the implementation of Dolby Atmos used for Ultra HD Blu-ray is described in the following way "Atmos data on Ultra HD Blu-ray actually an extension to TrueHD that is folded into the bitstream to maintain backwards compatibility."

Yes, I opened it in VideoReDo and exported it to MKV. (I know this software doesn't support 10-bit, but I wanted to test the audio.) The audio was exported as 7.1 PCM. Do you expect this to be equal to the original audio?

Your MKV appears to have just the TrueHD audio part. If you use a sound system that is capable of fully supporting Dolby Atmos, the TrueHD audio on the MKV may not sound the same as the original Dolby Atmos soundtrack on the UHD Blu-ray. However, the 7.1 PCM audio will sound the same as the 7.1 channel TrueHD audio.

Can I edit this PCM track in Vegas Pro and export as PCM, and re-mux it back into the MKV?

And as for video, yes, I must edit the 4K 10-bit HEVC in TMPGEnc. This will have to be a two-step process: edit the audio losslessly in Vegas Pro (if possible) and edit the video in TMPGEnc, and mux the streams together. Unless you have a better suggestion.

I don't have Vegas Pro nor have I tried it so I don't know exactly what it can and can't do.

[ogrgkyle]

Do you know of any software options for editing this MKV Atmos stream and re-encoding as Atmos? What options are there, even if they're expensive?

[Ennio]

You can give Audacity a try.
With eac3to you can decompress 7.1 TrueHD to a single 7.1 pcm file. Use *.w64 as output type. W64 can be opened in Audacity for editing. This may be more convenient than extracting to 8 single mono wavs and importing these piece by piece.
In settings --> export, Use Advanced Mixing Options. Otherwise Audacity exports to default mixed down stereo.

[Edit] You beat me to it. As far as I know editing/re-encoding Atmos can only be done with Dolby software.

[Cornucopia]

usually_quiet & Ennio are correct.

When you say "editing", I assume in this instance you are meaning cutting/trimming, and with that definition, only Dolby software is currently able to do it.
If you mean adjustment of elements, balance, placement, etc, you are really talking about re-mixing, and the only way to do that is to go back to the multi-track masters and remix on a Dolby Atmos-enabled DAW (e.g. AVID Pro-Tools). You would need to have access to those assets and permission from the producers to work with them.

Scott

[ogrgkyle]

Yes, I mean cutting Atmos audio and applying fades between cuts. Can I import the Blu-ray Atmos audio into Pro Tools (for instance), cut it, add fades and export as the same format?

[Luke M]

To my knowledge, the professional Atmos tools have no way to import Atmos, only export.

So the only way to edit Atmos would be to (somehow...) render to 7.4.1 PCM, edit, then export to Atmos. Of course the "object" metadata would be lost, but at least you would have height channels.

[ogrgkyle]

Can you help me understand what is the noticable audible difference between Atmos and 7.4.1 PCM audio? And by the way, what is 7.4.1 compared to 7.1? I thought this was 7.1 audio.

[usually_quiet]

Can you help me understand what is the noticable audible difference between Atmos and 7.4.1 PCM audio? And by the way, what is 7.4.1 compared to 7.1? I thought this was 7.1 audio.

The "4" indicates there are dedicated channels for 4 additional surround-sound "height" speakers positioned above the listener.

Dolby Atmos provides an even more realistic three-dimensional experience than ordinary surround sound, assuming that the sound engineers did a good job and the sound system is designed for Dolby Atmos. Sounds can appear to come from anywhere within 360° and appear to move with their sources. You can find more in-depth answers to your questions using a decent search engine.

[Cornucopia]

Atmos recommends, but does not mandate, additional "height" surrounds. It can actually work with any reproduction system, from 2.0 to 22.4.2 (or similar IIRC). Because it maps the object-oriented atmos elements onto one's existing reproduction system as optimally as is possible based on the limitations of that system. Obviously, 2.0, or even 5.1, is much less optimal of a mapping and so less accurate than something like a 22.2.1 system.

Most atmos titles include a standard, channel-based layout as either a compatibility backup layer or as a background "bed" or both.

There is no known current way to "extract" the object sound elements in isolation in order to rework (unless you could map to a system that had 100.100.100 or something, then you might get close), so there is no "editing".

If you want to map to standard channel layouts, such as 7.1, or 7.4.1, you can. But from that point you have a standard layout that you would edit using standard tools and mix to a new standard master. And once that standard master has a mix of elements placed as partial "phantom" signals throughout the various channels, it wouldn't work trying to encode them as new atmos object elements - they wouldn't be singular elements anymore, but multiple mini-mixes.


Scott

[ogrgkyle]

Thanks, your posts are extremely helpful. So let's say I'm content with losing the Atmos object data, if I can map it into 7.4.1 first. How can I do this? I haven't found a way with ffmpeg.

EDIT: Thinking on this more, I probably just need to extract the TrueHD 7.1 audio stream and forget about the Atmos audio. I can't find any way to decode and convert Atmos. Now I just need to extract the TrueHD 7.1 audio to a PCM 7.1 file. With VideoReDo TVSuite 6, I'm able to export the MKV with PCM 7.1. Then with ffmpeg, I extracted the audio stream from the MKV and dumped it in a .w64 file.

Now when I look at this .w64 file in Vegas Pro, I see five tracks:

Track #1 (Channels 1/2)
Track #2 (Channel 3)
Track #3 (Channel 4)
Track #4 (Channel 5/6)
Track #5 (Channel 7/8)

Is this the correct configuration for 7.1 audio?

[Ennio]

This is a recognizable configuration as any. Audacity would display only the first two channels as one stereo-track, where all other channels are mono tracks. Matter of interpretation, I'd say.
Editing audio, more important is that you realize what track represents what channel.

Not knowing Vegas Pro, I think that your stated

channels 1 & 2 are L and R

channel 3 = C

channel 4 = LFE

channel 5 & 6 = Lb and Rb

channel 7 & 8 = Ls and Rs

But always check. Use you ears. Especially keep an eye out on the last two surround channels (5,6) and (7,8), they can be swapped sometimes. In a discussion from ages ago I learned that the back-surrounds usually are displayed first, and then the side-surrounds.

[Peter Sagan]

MKVToolNix can cut/trim Dolby Atmos using simple timestamps without losing any object information, just saying.

[ogrgkyle]

Are you saying you can use timestamps to skip (not literally cut) portions of an MKV?

[Ennio]

MKVToolNix can cut/trim Dolby Atmos...

Damn, I remember cutting out a clip from a movie once that had TrueHD sound. This seems ages ago.
I never gave it further thought, but am now eager to do some tests with Atmos.

Thanks for this revelation, Peter Sagan

[ogrgkyle]

Ennio, please let me know if you find a way to cut and/or edit Atmos.

[Cornucopia]

@Peter Sagan, I believe you just lucked out.
Unlike Dolby E, Dolby Digital (AC3), DD+, TrueHD (with or without Atmos) does not use packet frames that are evenly spaced along with video's frame cadence.
So if you cut on the video frame, it is a crap shoot whether it cuts on an audio packet frame boundary or not. And though I don't know enough about the packet innards, there is a possibility of data corruption or mismatch with timestamps as well, even if you do manage to cut on boundaries.

Scott

[Ennio]

...TrueHD (with or without Atmos) does not use packet frames that are evenly spaced along with video's frame cadence.

I'm having trouble to understand what you're saying with "evenly spaced along". Thinking of a timeline, would you mean that videoframe timecodes don't match with audio (-packets/frames) timecodes? If I'm missing something here, can you please explain?

[Cornucopia]

Yes, that's what I mean. Compressed bitstream audio is not sample based like lpcm, nor is it based on video frames (it's not video). It is a continuous stream of compressed data, but luckily that data has been chunked together in timestamped packets. In Dolby E it is designed to align those packet boundaries at the same points as video frame boundaries. AFAIK, no other format is intentionally set out that way, so alignment of both A & V at any particular point for those others would just be a stroke of luck (though overall, statistically there should be a number of those alignments throughout a normal title).
That's one reason why many editors, when given compressed audio, will decode it to lpcm internally for the timeline, and require a full recompression on export.
Tools like mp3cut work with mp3 & aac, and likely parse the timestamps to find those packet boundaries, so it can edit losslessly, but then it doesn't have to work with video simultaneously.

Scott

[Ennio]

I went Gung Ho and did a quick & dirty test with a movie containing Atmos sound. Using mkvtoolnix' splitting option, I extracted a 5 minute clip. I took care that the beginning of the clip was not the beginning of the movie.
Taking a look at the result with MediaInfo, it indeed states the audio as TrueHD with Atmos. Having no Atmos AVR where I am at the moment, I was however able to test it on a AVR with a TrueHD decoder. It locked on "Dolby TrueHD" indeed, both audio and video played back ok and were in perfect sync. Of course the question to Atmos still has to be answered when I'm playing this on my Atmos machine.
As a sidenote, the duration of the clip wasn't exactly 5 minutes; this will be due to mkvtoolnix being able to cut on video keyframes only.

Regardless whether Atmos will play or not, I took a closer look at what MediaInfo tells me about Atmos in general. It says, a.o.:

Sampling rate: 48.0 kHz
Frame rate: 1 200.000 FPS (40 SPF)

...chunked together in timestamped packets.

So, each second would consist of 1200 Frames. I assume these "Frames" would be the "timecoded packets" you mentioned? Where every Frame would be 40 samples. So, each second would indeed give me 1200 x 40 = 48000 samples. This would all make sense to me.

Now, because of the mere fact that the splitting function works, could the following be valid?

"Next to be able to cut video at a keyframe, mkvtoolnix can also cut on a whole audio-frame, near or nearest to the video-keyframe. It doesn't matter whether the two timecodes don't line up. The timecodes in both audio- and videostream are rewritten before remuxing them back together."

What do you think?
When I find the time, I'll do more testing. It's interesting to find out if more precise cuts could be made when only Atmos audio would be imported. And of course, whether multiple cuts can be joined together into one continuous stream.