Blu ray to MKV: Any reason to keep anything but the best audio track?

[ziphnor]

Hi,

I am in the process of (losslessly) backing up some Blu ray discs to MKV files. In doing so i have noticed that many discs have several versions of the same audio track, for example 5.1 LPCM, 5.1 AC3 and sometimes an additional stereo AC3.

What i am doing currently, is to just keep the 5.1 LPCM audio track (or whatever other track that has the highest quality). I currrently dont have any surround sound playback options though.

I am sort of assuming that when i playback the 5.1 LPCM audio on a TV with stereo speaks (through PC connected via HDMI) that the audio is converted down to stereo yielding the same quality (or better as the source is uncompressed) than the stereo AC3 track on the disc. Is this a correct assumption? And if it is, why bother putting the inferior quality tracks on the disc in the first place?

Sorry if this is a stupid question :)

[madshi]

There are usually 5.1 lossless (PCM, TrueHD or DTS-HD Master Audio) and a 5.1 lossy variation (AC3 or DTS) on the disc. The lossy variation can be helpful if you transport audio through SPDIF connection because SPDIF doesn't transport multichannel lossless audio. However, if you transport audio through analog connection or through HDMI, there's no real need for the lossy audio tracks, anymore.

Those lossy 2.0 audio tracks on the discs are usually commentary tracks.

[ziphnor]

Thank you for the quick answer.

The lossy variation can be helpful if you transport audio through SPDIF connection because SPDIF doesn't transport multichannel lossless audio.

I transfer audio and video over HDMI currently. What would happen if i did connect over SPDIF and played back an MKV containing only LPCM 5.1?

[madshi]

What would happen if i did connect over SPDIF and played back an MKV containing only LPCM 5.1?
Depends on the software and drivers you're using. The "correct" thing to do would be to either only send LPCM 2.0 or to encode on the fly to AC3 5.1. Both are valid options. Of course if LPCM 2.0 is used, a proper downconversion (where the surround channels are mixed into the final stereo data) should be used. Depending on your drivers/software it may also happen that the surround channels are simply dropped.

[ziphnor]

Depending on your drivers/software it may also happen that the surround channels are simply dropped.

Thanks. I think i will keep the AC3 track then, they are after all relatively small compared to the huge LPCM track :)

Btw, now that you are being so helpful:
Are there any potential problems with ripping the LPCM tracks to WAV (as done by tsmuxer)? For example, is all necessary information about which channel is which maintained?

[tebasuna51]

Btw, now that you are being so helpful:
Are there any potential problems with ripping the LPCM tracks to WAV (as done by tsmuxer)? For example, is all necessary information about which channel is which maintained?

Changes between lossless formats must be exact, but tsmuxer have some bugs (extrabytes at end of wav files) than can cause problems.

Use eac3to instead.

[madshi]

Ripping to WAV is perfectly safe and contains all necessary information, as long as the ripping application works correctly. However, WAV files bigger than 4GB (or even 2GB) can make problems with some applications. E.g. I know that tsMuxeR cannot *read* WAV files bigger than 4GB. I don't know if it can store such files. If you want to go sure, you can use "eac3to" for demuxing to WAV. eac3to has no problems with either reading or writing such large WAV files, and it can also transcode audio to many other formats of your choice.

[tetsuo55]

I do the same thing, i hate searching for discs...

Anyway

I keep:
-The highest quality audio
-All commentary tracks
-The longest version of the main movie
-English subtitles (for the hearing impaired), this helps a lot with muddled dialogue too

It would be great to keep all the chapters, but that is difficult at best.

I wish there was a free(preferably open source) application that would do:
DVD/Blueray/HDDVD/DVD-AUDIO/SACD remux to MKV
While keeping:
-audio tracks
-Include all versions of the movie, selectable from the splitter menu(adds only a little overhead per different version)
-Subtitles
-Chapters


Anyway, i configured FFdshow to upmix/downmix all channels to the number of channels i have.

[tebasuna51]

... However, WAV files bigger than 4GB (or even 2GB) can make problems with some applications. E.g. I know that tsMuxeR cannot *read* WAV files bigger than 4GB. I don't know if it can store such files...
Exact (I forget this second problem). TsMuxer cannot write files bigger than 4GB, split the output in 4 GB max wav files.

With eac3to you can output also W64 files, like WAV but with support files > 4GB.

[madshi]

tsmuxer have some bugs (extrabytes at end of wav files) than can cause problems.
Didn't know that!

TsMuxer cannot write files bigger than 4GB, split the output in 4 GB max wav files.
Ah, that makes sense. Can it read these splitted 4GB WAV files in for muxing again? Probably not? :(

[ziphnor]

Regarding the 4GB limit of WAV files: It hasnt been a problem for me since mkvmerge can merge multiple WAVs into one track.

Changes between lossless formats must be exact, but tsmuxer have some bugs (extrabytes at end of wav files) than can cause problems.

Damn, so i should re-extract the LPCM tracks of the 5 Blu rays i have processed so far?

[tebasuna51]

With 16 bit wav files the output audio data is always 4 bytes more.
No mather the BlockAlign value these 4 bytes makes wrong (not exact num of samples) the header, and the channels can be misaligned if are concatenated.
Accept WAVE_FORMAT_EXTENSIBLE headers but don't preserve always the ChannelMask then the output channels are distinct than input channels.

These 4 bytes is the mini-header needed in tsmuxer-lpcm format.
I don't know if is related with m2ts format or is only a TsMuxer issue, but can't support the full range value of ChannelMask.

With 24 bits wavs the extrabytes are much more (5760 in a 4 chan 96KHz) and I don't know what contain (maybe only garbage)

Of course don't accept concatenate input wav files.

[tebasuna51]

Regarding the 4GB limit of WAV files: It hasnt been a problem for me since mkvmerge can merge multiple WAVs into one track.

Damn, so i should re-extract the LPCM tracks of the 5 Blu rays i have processed so far?

If the wavs was obtained with TsMuxer is recommended.
I use WaveWizard to concatenate and I see also clikcs at beginning of each wav file then there are problems at the beginning and at the join point.

Use Eac3to to output WAV files >4GB, mkvmerge can read these WAV files.

[tetsuo55]

Does MKV even support E-AC3,TrueHD and DTS-HD??

[madshi]

Does MKV even support E-AC3,TrueHD and DTS-HD??
E-AC3 and DTS-HD: Yes. TrueHD: Currently no.

[tijgert]

What is the command for eac3to for extracting LPCM audio from a m2ts file then?
(cheers)

[tebasuna51]

Raw pcm:
eac3to source.m2ts TRACK: output.pcm

Multichannel wav:
eac3to source.m2ts TRACK: output.wav

Monochannels wavs:
eac3to source.m2ts TRACK: output.wavs

Multichannel w64:
eac3to source.m2ts TRACK: output.w64

[tijgert]

Why should one opt for extracting audio to .w64 files instead of .wavs files??

[tebasuna51]

Some soft (like tsmuxer and others) don't accept wav files >4GB but accept .w64 files.

[Ghitulescu]

Lossless audio tracks are usually for those having above average HiFi chains or for purists. They can be transported only using high-speed digital interfaces, like the HDMI.

5.1 lossy formats (DD, DTS) are generally present to insure the compatibility with older interfaces/devices, as they can be transported over S/P-DIF (mostly optical). So an expensive 5.1 AVR of an older generation may be still used. 7.1 channels are not always "true" but most of the time (nowadays) are simply interpolated/upmixed. 5.1 channels can also be "true" but also upmixed (most spaghetti westerns that are presented in 5.1 originally had just a mono track). This is also why the lossless multichannel solutions can be "downgraded" to a "compatibility kernel".

2.0 lossy containing the main audio are there also for compatibility issues, in case one has only the BD player and the TV set. While any (AFAIK) player can downmix the multichannel to stereo, having the studio mix should be better than the downmixed stereo.

Keep the tracks that you need.

[Overdrive80]

FLAC wouldnt be a good election, would be?

[nevcairiel]

FLAC is lossless audio, so if you need/want the perfect quality, and have the disc space to spare, its a good choice to use. :)
It'll certainly be smaller then an uncompressed PCM track, at least.

[kieranrk]

It'll certainly be smaller then an uncompressed PCM track, at least.

And smaller than a TrueHD or DTS-HD lossless track.

[tijgert]

But which amps accept flac??

[tebasuna51]

But which amps accept flac??
You can send PCM multichannel, by HDMI, with a compliant player (PC or standalone Xtreamer, etc.)

[hubblec4]

to keep the DTS-HD or TrueHD audio is flac. this is the best choice! Perfect lossless copy and smaller filesize.
The most softwareplayers can handle flac and a lot of hardwareplayers too.

Maybe in future the AVC-Reciever's have a flac-decoder inside.

My Bluray movies are backed up to mkv-file and i play this on a little pc. output is hdmi. thats perfect for video and audio.

[tijgert]

I found that converting PCM to DTS-HD (MA of course) gives the same lossless audio quality AND allows it to be output on both HDMI and older fashoned digital outputs like optical and coax. Best of both worlds really... (which makes me wonder why studio's bother at all with LPCM when DTS-HD (MA) or TrueHD is just as good but smaller...)