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Why do Audio and subtitles have multiple levels? Image below for reference

For Subtitle it says "PSG English" and "PSG English (forced only)". Do I have to select both? What happens if I select only one? In HandBrake only one shows up even if I select both levels. Does it have anything to do with foreign language scan?

For Audio it says "TureHD Surround 7.1" on the main level and "DD Surround 5.1" on the sub level. By default the main level is not selected. In handbarke they do show up as 2 separate streams. Why is the main level not selected by default? Is not not a real level? like a virtual level or something? Can I select just the main level and unselect the sub level? wouldn't that give me the best audio? or will that create any problem

As an additional amplification of one point in the FAQ linked above, MOST movies and TV series I've encountered do NOT have any "forced" flags set, so the "Forced only" track will be removed as empty. If I didn't have a copy of the movie Avatar, I'd doubt that the flag is ever used.

I suspect the original reason for creating a separate track is that many players have no support for the forced flag, even when present; They only know that subtitles are "off" or to display a particular track.

Actually, there's some more flagged forced subs on German Blu-Rays cause we often get one subtitle track that translates signs on buildings or letters read by the protagonist or something.

Thanks about the subtitle explanation, what about the Audio?

Multiple levels of audio is because "loss less" tracks like DTS HD have multiple components to them; a "lossy" track (DTS) and a "differences between lossy and loss less" track. "TrueHD" is the same, where "Dolby Digital" is the lossy track within TrueHD.

Devices that do not understand the loss less portion ignore it, while devices that can play loss less will use everything. But a lot of devices that play MKV cannot pull the lossy track out of the combined track, so MakeMKV offers to make two separate tracks - one with just the lossy part, and the other with both.

Yes, it takes up more space in the file, but it maximizes compatibility.

Woodstock wrote:Multiple levels of audio is because "loss less" tracks like DTS HD have multiple components to them; a "lossy" track (DTS) and a "differences between lossy and loss less" track. "TrueHD" is the same, where "Dolby Digital" is the lossy track within TrueHD.

Devices that do not understand the loss less portion ignore it, while devices that can play loss less will use everything. But a lot of devices that play MKV cannot pull the lossy track out of the combined track, so MakeMKV offers to make two separate tracks - one with just the lossy part, and the other with both.

Yes, it takes up more space in the file, but it maximizes compatibility.

Thanks for the explanation, this is really helpful. Follow up question, if I am going to play play the MKV using PowerDVD only or rip it with Handbrake only, then can I just select the main audio? In this case (referring to the screenshot above) "TrueHD Surround 7.1 English" only and I should be okay?

I cannot make recommendations on audio for PowerDVD, although it is quite possible that it handles full TrueHD. Handbrake can handle TrueHD as a pass-through, so if your playback can handle it, it should be fine to not select the lossy audio portion as its own track.