Keep HD audio on MKV ?

[Nico8583]

Hi :)
I'm going to encode my Blu ray collection to MKV and I have an hesitation : do I keep HD audio (DTS Master, DTS HD, TrueHD) on MKV or is it useless ?
What do you do on your backup ? ;)
Thanks !

[DarkSpace]

What I'll say is purely technical, because my optical drive isn't working right now and that means no backups for me.

You can of course keep the HD audio as it is, and it won't hurt you except that it takes space as long as you can decode it properly.
In the case of DTS-HD audio, you may or may not have difficulties in decoding the full HD stream (e.g. LAV Filters is able to utilize a dtsdecoderdll.dll if you have one to decode DTS(-HD) streams), but aside from decoding issues, you should be fine in keeping the audio. You can, of course, just as well convert the audio to a format of your choice (PCM, FLAC, AAC, the list goes on) and use that instead, but that's purely your choice.
What I personally would do is to convert all the lossless audio to FLAC, and leave the lossy audio untouched. That way I would achieve consistency for the lossless audio tracks stored on my HDD, regardless of what format they may have had originally, while not furthering the loss of data from the lossy audio tracks (however inaudible and purely theoretical that loss may be). This, of course, assumes that I have sufficient HDD space at my disposal.

[Nico8583]

Thanks for your advise :)
I think also it's better to keep HD audio because I can allways change my choice in the future and simply convert HD to lossy, but not the invert. I don't know if there is a big size difference between lossless and lossy audio but disk space is not a problem. My only doubt was to play DTS-HD on device that supports only DTS (or TrueHD on AC3 supports only) : do all devices can play only core if necessary ?
I've never tried FLAC, but I think I prefer leave HD audio untouched if I decide to keep it. Is there a big space gain between DTS-HD and FLAC ?

[Mole]

He meant using FLAC on any PCM uncompressed audio streams, while not doing anything to lossy audio such as DTS, AC3, TrueHD.

For PCM audio, you'll save about 50% when converting it to FLAC, which is lossless, so you'll keep exactly the same quality as PCM.
I'd also recommend always compress any PCM audio to a lossless format such as FLAC. You'll save a lot of space while keeping exactly the same quality as source.

Are you just remuxing the BDs to MKV or are you also re-encoding the video?
If you're only remuxing, then it makes sense to mux the complete audio as well.

However, if you're re-encoding the video, then I don't see the reason to keep the full audio, while the video has already been re-encoded to lower quality. You might as well keep only the DTS-core and the AC3 in TrueHD.

[Nico8583]

Thanks also :)

OK for PCM and FLAC, I'll try that when I'll get a PCM track.

Yes I'm re-encoding video but with a CRF 18 and a slow or slower preset, so I think quality is not very affected with these settings ? Even with these values, you think HD audio is useless ?

[Mole]

Well, if you're already re-compressing the video and in your opinion, the quality of the video is "not very affected", then you might as well just keep only the DTS-core and AC3 in TrueHD, because I'm pretty sure for you, audio quality will also be "not very affected".

It really only makes sense to keep the full original audio if you're just backing up your BDs by remuxing them to MKV for more convenient playback. If your video is already re-compressed, you might as well save more space by not keeping the full audio.
Chances are that your player setup may not even be capable of playing the full DTS-HD and TrueHD audio and is probably simply playing the DTS-core and AC3 audio.

I'm sure you really won't be hearing much difference between DTS-core and DTS-HD or even AC3-640 and TrueHD.

[Nico8583]

OK thanks :)

Perhaps with a very good material and very good eyes differences would be visible :D

Do you see any difference between original video and encoded video ? Same for audio ? It's just to know how could it be possible ;)

[Mole]

Actually, there are many more factors involved.

First of all as you say, it depends on the quality of source.

But another factor is also the hardware you're playing it on.

For example, if you play it on a 32" TV and 60" TV, you will of course be able to notice the difference in quality more if you play on a big TV than a small one.

For audio it depends on your audio equipment as well as the environment you usually watch your movie in. If you have a dedicated home theater room, then of course you'll be able to notice the small difference in quality, while if you just play it in your living room where there may be other people around such as other family members, then of course the background noise that other people make will make an impact.

If your opinion in that CRF=18 is good enough video quality, then I'm pretty sure the DTS-core and AC3-640 will be good enough audio quality for you too.

I can tell you this, unless you have really good audio hardware (amplifier and speakers) and is playing in a dedicated noise proof home theater room, you won't really be able to notice much difference between DTS-core and DTS-HD or AC3-640 and TrueHD.

[DarkSpace]

He meant using FLAC on any PCM uncompressed audio streams, while not doing anything to lossy audio such as DTS, AC3, TrueHD.
Actually, there's more than one thing wrong with your statement:
1. I clearly said that I'd convert any lossless audio to FLAC for consistency. I never tried to limit this to PCM (although that is the area where I would expect the greatest gains in compression).
2. I did say I would leave lossy audio alone, that is true. However, TrueHD is lossless, and as such would be converted to FLAC as explained above.

My only doubt was to play DTS-HD on device that supports only DTS (or TrueHD on AC3 supports only) : do all devices can play only core if necessary ?
You're free to do whatever you want to the audio, of course.
For DTS-HD, there will always be a DTS core that can be played by hardware without support for decoding the HD extensions (that is the whole reason there is a standard DTS core in DTS-HD audio).
For TrueHD, what will happen depends on your audio track: On BluRay discs, TrueHD tracks are typically stored in such a manner that they contain an AC3 track which will be played by devices that can't decode the TrueHD data. However, the TrueHD track is, unlike the DTS core for DTS-HD audio, completely separate from the TrueHD audio as far as decoding is concerned*, so I would expect demuxers to only demux the TrueHD track, leaving the AC3 track alone, unless instructed otherwise. As such, you'll most likely have a standard TrueHD track without AC3 "fallback solution", which means your device will likely just fail to decode the track.
Of course it is possible to extract the TrueHD track with the AC3 track interleaved (e.g. eac3to can do this if you specify ".thd+ac3" as extension rather than just ".thd" for the track), and if you do that, it is the responsibility of the muxing application to store the track correctly (I think I once tried muxing a thd+ac3 track to mkv with mkvmerge and it kept only the TrueHD data, but I really am not sure - I was only curious whether it would output something at all). In that case, I expect that you have a reasonable chance that your device manages to fall back to decoding the embedded AC3 track.

* In fact, as far as I know, the AC3 track embedded in the TrueHD track could contain completely different audio even - say, TrueHD is audio from Movie 1 and embedded AC3 is audio from Movie 2!

[Mole]

You're right, I forgot that TrueHD is lossless.

How big difference in file size is it between TrueHD and FLAC?
Will FLAC also preserve all the normalization and dynamic range metadata which would be processed properly by player?

It appears that for MKV, you'll have to mux the AC3 as a separate track from the TrueHD. For example TrueHD as track1 and AC3 in track2 and manually change track if the software or hardware doesn't support TrueHD.

I am however starting to realize the advantage of converting TrueHD to FLAC in that there will be less problems playing a FLAC audio than TrueHD. This assuming of course that your system is configured properly in order to be able to convert the TrueHD to FLAC.
But once the audio is FLAC, then you can play it on any system regardless if it's able to decode TrueHD or not.

[DarkSpace]

How big difference in file size is it between TrueHD and FLAC?
I never actually paid much attention to the size difference between TrueHD (or DTS-HD MA) and FLAC, but I believe it's safe to say that the FLAC was consistently smaller: I don't remember the FLAC being larger than the original audio, and that's the kind of thing I'd expect to remember if it happened.

Will FLAC also preserve all the normalization and dynamic range metadata which would be processed properly by player?
I don't think it will. I do, however, not want my lossless data to be normalized, or to have its dynamics adjusted, by the decoder, so for me, that is no issue I spent time thinking about. If you want those metadata, that is a strong reason to keep the data in TrueHD, of course.

It appears that for MKV, you'll have to mux the AC3 as a separate track from the TrueHD. For example TrueHD as track1 and AC3 in track2 and manually change track if the software or hardware doesn't support TrueHD.
I see, thanks. I can't test at the moment, so I am grateful to you for verifying my statement in my stead.

I am however starting to realize the advantage of converting TrueHD to FLAC in that there will be less problems playing a FLAC audio than TrueHD. This assuming of course that your system is configured properly in order to be able to convert the TrueHD to FLAC.
But once the audio is FLAC, then you can play it on any system regardless if it's able to decode TrueHD or not.
Which is precisely the reason I would convert any lossless audio to FLAC: I simply would have to bother with decoding all the different formats only once, and from then on, I'd have to take care only of decoding FLAC. Of course, the same works for any other codec of choice, too.

[Nico8583]

Thanks to both :)

FLAC seems to be a good choice, but is it playable with standard device (TV, Standalone BD player...) ?

I don't have dedicated room to watch movies, I don't have a really good hardware so I think HD audio should be useless for me. And if all devices cannot read TrueHD simply, it is a disadvantage for me...

[SeeMoreDigital]

My only doubt was to play DTS-HD on device that supports only DTS (or TrueHD on AC3 supports only) : do all devices can play only core if necessary ?

You shouldn't have any problems with DTS audio. But as mentioned previously, it's a different issue with DolbyDigital audio in MKV because the DolbyDigital 'core' is automatically removed by the Matroska muxing application. So you'll need to add it as a separate stream?

[Nico8583]

Thanks for confirmation, so if TrueHD in MKV cannot be used as 'core', I'm not interested because if I want to play movie on another device I'll can not do that...

So my conclusion is : if I don't have a dedicated room with good material (video and audio), keep original video (without re-encoding) and audio (HD) would be useless. Is it right ?

[Mole]

Yes, something like that. You said yourself that you think CRF=18 is almost same quality as original DVD.

Then you can think that DTS-core compared to DTS-HD would be similar to video at CRF=18, if you know what I mean.

[Nico8583]

I think CR=18 is very similar to Blu ray quality yes, and I think also I'm not alone ;)