AC3 Passthru of DTS Audio--Why Does it Work?

[StPatty33]

Hey, all!
I've been using Handbrake to backup my personal Blu-ray library for a couple years now, and am getting around to re-doing some of my older discs that I had encoded without surround (I believe to maximize compatibility with the older Apple TV's).

Recently I switched to MKV format from MP4, so that I could passthru PGS subs and some of the higher quality audio formats. I've discovered that some audio files, such as DTS, are quite large (1 to 1.5g), whereas an AC3 Passthru of said DTS file is more like .5g. That leads me to a couple questions:

1) Why does an AC3 Passthru work on a DTS file? Do all DTS files have an AC3 core or something? Will I ALWAYS be able to do a successful AC3 passthru on your typical 5.1 files, or will it fail with certain formats and do something crazy like turn a DTS 5.1 into a DTS stereo file, like when you try to DTS Passthru on an MP4 file?
2) Do you find the extra space used by DTS v AC3 is worth it? On all movies, or just action blockbusters, etc?

I've been using auto-passthru since switching to MKV, but I get the feeling many of my titles don't need the extra 1gb of file size to go DTS over AC3. Any advice or insight is greatly appreciated!


Bonus question: I've also started doing many titles in 265 v 264. What's your opinion on the matter, and why?

Thanks again!

[rollin_eng]

AC3 and DTS are different formats.

AC3 passthrough of DTS audio will re-encode it to AC3 if you have AC3 fallback.

As to which is better that will depend on your equipment and your ears.

Can you please post your log.

[Woodstock]

Depending upon your version of handbrake, which would be obvious if we had the required lots, DTS may or may not "pass through". Since DTS is not the same as AC3, as rollin points out, you normally won't have an AC3 track in the output if your settings are correct.

As for why you're doing x265, maybe, "because you want to"?

I only have one device that can play an x265 file, so I wouldn't make the choice you have.

[hogfan]

Personally, I find DTS (Digital Theatre Systems) tracks to sound quite a bit better than Dolby Digital (AC3). Not that Dolby Digital is bad, but if a DTS track is available I always prefer it. There is never really a time that you should re-encode a DTS track to an AC3. If you are wanting to reduce the audio track size, a better option would be to re-encode the source DTS or Dolby Digital (AC3) track to a multi-channel AAC format. From what I have seen, a bitrate of 256K seems to be popular. However, since I have a receiver and 5.1 surround setup, I prefer to stay with the source DTS or AC3 audio track in my Blu Ray encodes.

Now for the 7.1 audio tracks (DTS-MA (Master Audio) or DD-HD), you will find that the 7.1 layout DTS audio track will have a "Core" DTS track within it. This core track is DTS 5.1 audio, so you can just grab this "Core" track if you only want 5.1 instead of 7.1.

[Susan_J]

Thank you, hogfan! I'm a new handbrake user and have spent the last week or so looking for exactly the information you provided in your post.

I've found many recommendations about video, but very few about audio and not as clearly expressed.

No logs, just my thanks!