Blu-Ray backup -> MP4 with optional subtitles?

Question

I have a number of BluRay discs which I have backed up to my Windows 10 Pro 64 computer using MakeMKV, resulting in folders with BDMV, CERTIFICATE, and MAKEMKV subfolders. I want to re-encode and compress the movies to MP4 files using Handbrake 64-bit 1.0.7, to be played back on iDevices, from a USB stick on my TV, etc. I would like to include any "forced" subtitles, when a movie is in my own language (English) but which has sections in other languages which have English subtitles. I would also like to include English-language subtitles in the MP4 file, in such a way that they can be displayed or not displayed as preferred by the viewer. This doesn't seem like it ought to be difficult to do, but for some reason I seem to have done this incorrectly every time I try, and when I try to figure out what is wrong I have been unsuccessful. Any pointers on where to learn to do this, or simply instructions on what I ought to do, would be much appreciated. Thank you.

Answer 1

Subtitles can be set up slightly different ways on a Blu-ray depending on how it was originally encoded, and this affects how you will re-encode into an MP4 container. Here are the more common ways I have seen, in the context of only caring about primary language subtitles that match the audio stream (no foreign subtitles, no director's commentary subtitles):

1. Forced subtitles pre-burnt into the video stream, regular subtitles encoded as subtitle streams.
2. Forced subtitles in one dedicated stream set as default (may or may not be flagged as forced), regular subtitles encoded as separate subtitle streams.
3. All subtitles encoded in a single stream, no default set. The Blu-ray format allows for code to run to help manage playback, which can dynamically show forced subtitles even if no subtitle stream is enabled.

This means that unlike the DVD format, encoding subtitles from a Blu-ray is not a cut and dry process.

Using Handbrake, I recommend running a foreign audio scan first as a test run, even if there is only a single primary language subtitle stream. This will scan all subtitle tracks that are flagged as the same language as your first audio track (e.g. you encode English audio, it scans all English subtitle tracks) looking for subtitles with the "forced" flag set.

Review the output: it will tell you which tracks exist, how many subtitles each contains, and how many are forced. Generally speaking, forced subtitles are ones used when there is foreign dialog in the video, translated back into English. You can supplement this by playing the disc using licensed Blu-ray playback software (e.g. PowerDVD) and seeing which subtitle track it selects by default. This is not an exact science: you will need to perform some trial and error.

If the forced subtitles are pre-burnt, there is nothing more to do: simply select the regular subtitle stream.

If forced subtitles are in a dedicated stream, select that stream as one subtitle track and mark it "default." This means any player should select it automatically and display the forced subtitles.

If all subtitles, including forced, are in a single stream, that too is easy. Simply select the subtitle stream twice. Handbrake will encode that one original stream as two streams in the output. For the first one, select "forced only" and "default" as the options. For the second instance of the stream, select nothing. Now when a player plays back the video it will default to the forced subtitles in stream one. If you want to see all of the subtitles, select the second (non-default) stream in your player and it will show all of the subtitles.

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There is an edge case that combines options 2 and 3 above. I have only seen this on one disc. Sometimes the forced subtitles will be in some weird track number. For example, regular subtitles are track 1, forced will be track 9 or 10 and not defaulted but show anyway due to the executable code on the Blu-ray instructing the player to show them even if they are not selected. This highlights the importance of testing: carefully review the activity log when using foreign audio scan, and review the output file to ensure the correct subtitles are selected (e.g. you want the "real" subtitles, not director's commentary) and that during a scene where you know there are forced subtitles, they actually display.