Need help with shrinking Bluray-remuxes.

[monkeyeater]

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[hello_hello]

There's quite a few free encoder GUIs for re-encoding the video to reduce the file size. Depending on how much you want to reduce it, you can keep the original audio rather than convert it, or you can convert the audio to reduce it's file size, but converting the audio won't do anything to make it sound better, just smaller.
I don't know of any free programs which can convert to DTS, but you could probably convert the TrueHD audio to FLAC which is a lossless compressor and may reduce it's file size somewhat. Other than that, most people probably convert it to AAC or AC3. It depends on the device you're using for playback and what it supports etc.
Or if there's also an AC3 audio stream on the disc, you could just keep it.

Generally you'd re-encode the video using the x264 encoder while using it's quality based encoding mode. You specify a quality setting (called a CRF value) and the output file size will vary as a result (according to how hard the video is to compress) but the quality will be the same relative to the original each time. If you don't need extreme quality, it's probably best to resize down to 720p when encoding as that produces a much smaller file size for a given quality setting and as a general rule you don't lose much detail in the actual video, if any.
Reducing the file size to 720p when encoding will also speed the process up considerably.

So once you've re-encoded the video, if you're keeping the original audio, you'd open the original M2TS or MKV file with MKVMergeGUI, deselect the original video stream, add the MKV containing the encoded video, and save the output as a new MKV. Or if you're re-encoding both the audio and video the conversion program will usually output a completed MKV for you.

VidCoder is a popular program. Use it's "high profile" preset when encoding and select a CRF value which gives you the quality you prefer (you might need to experiment). The lower the value the higher the quality. The default value for the x264 encoder is 20. It'll produce a very nice looking encode. CRF18 is considered to be around the value where the encoder is "transparent". Values up to 22 or more can still look very good. Naturally the file size will increase as you lower the quality setting.

I use MeGUI myself but it has more of a learning curve than a program like VidCoder.

To give you an idea.... I re-encode most movies while resizing the video to 720p and re-encoding the audio as AAC using it's default quality setting. I use a CRF value of 18. The final file size varies from movie to movie, but it usually ends up somewhere between 3GB and 5GB. If you keep the original DTS audio rather than convert it, you could probably add an extra 1GB to that.

As it turns out, I've just finished encoding the original Pirates Of The Caribbean movie.... twice. Once at 1920x800 and again at 1280x534 (it's one of those movies where I can see a very small difference in detail between 1080p and 720p, but my other half wants a 720p copy, so I did it twice). It's about 2.5 hours long and I used a CRF value of 18 both times and for the video only, the output file size for the 1080p version was 12.1GB. The 720p version came in at 5.3GB, so in terms of file size it is a bit larger than average for a movie, but it's also longer. It only contains uncompressed audio which I didn't extract (I converted it to AAC) but if it had DTS it'd be around 1.5GB. The original AC3 audio stream was 755MB and after converting the uncompressed audio to AAC it's file size was 472MB.