Having a Hard Time Understanding MKV

[dualdivx]

Hello all!

I'm looking to finally digitally archive my extensive library of HD Blu-ray discs. However, I'm having trouble understanding the most popular ripping format for HD videos like this, namely MKV. Here is my issue.

Back in the day of ripping DVDs, a raw ISO or VOB folder would typically run right around the 8-9 GB range for a retail disc (and that was pretty consistent across the industry). Using DVD Shrink, you could easily get it down to a target of 4 GBs in order to get in onto a blank DVD-R. These two figures we're pretty consistent and all you had to worry about. I'm finding that not to be the case with Blu-ray and MKV.

I've seen Blu-rays ripped to the MKV format come in a variety of file sizes. For example, the exact same disc (depending on who ripped it) can be as large as 30 GB on the high end to as low as 3 GBs on the low end (with a 10-12 GB sweet spot in the middle, which I find to be the most common). My question is why? What is going on with the ripping that causes such large discrepancies in file size of each MKV? I personally don't see any noticeable quality difference between the three, but I'm sure there is some difference in settings/processing there and I'd like to understand what.

I want to make sure I settle on a good rule of thumb before I start archiving my collecting, as I'll only get one shot at it (as I have no intention of redoing all this work once finished, as it's going to take a while). Just want to ensure I hit a good target first time out.

Thanks!

[Cornucopia]

Those smaller bd "rips" are not really just rips, but rips+re-encoding at much lower bitrate. Though there is clearly some variability to bd main movie asset original sizes, I would gauge most (originals) to be in the 19-to-40GB range.

If you were to rip only, you would end up with either an ISO (for whole disc images) or M2TS file/folder structure (see "what is..." above).

Scott

[fritzi93]

I want to make sure I settle on a good rule of thumb before I start archiving my collecting, as I'll only get one shot at it (as I have no intention of redoing all this work once finished, as it's going to take a while). Just want to ensure I hit a good target first time out.

I don't think you can arrive at a good rule of thumb for target size. There's a case to be made for re-encoding to target size for storage purposes, e.g. to BD25 or BD9. But not from a quality standpoint.

As Scott pointed out, there's too much variability. You may think 10-12 GB is the sweet spot, but what does that mean? For some it will mean quality they can live with on their current display, for others it means "transparent". For yet others it will mean untouched, because they surmise that a better quality/larger display is likely to change what is acceptable quality, to them.

To take an extreme example, re-encoding Saving Private Ryan to 10-12 GB will result in a very noticeable quality loss. The movie is too long, and there's too much grain, which is difficult to compress.

I'd urge you to consider two alternatives:

1) Simply put main movie in MKV container as-is. If you want to do this job only once, there you are. MakeMKV can do this for you, and allows you to deselect unwanted audio and subtitle tracks.

2) Re-encode using quality based encoding. The most used tools here for that are all front-ends for the x264 encoder. A CRF value of, say, 18 is considered by many to be "transparent"; higher values will result in lesser quality. Output size will be unpredictable. For example, I can tell you that very clean animation for a movie like WALL-E (98 minutes), can be compressed as small as 2.81 GB using crf20 (Ripbot, Film Tune, slow preset, audio re-encoded to 640 kbps AC3, one subtitle track). Saving Private Ryan (169 minutes), on the other hand, comes out at 19.1 GB with the same settings.

Good luck.

[redwudz]

Since I still retain all my BD discs, I convert them to MKV H.264 with AC3 audio for ease of playback. I mostly use RipBot for BDs and VidCoder for DVD conversion.

I convert just the main movie.
I use two pass and set a target size of ~8GB. The main reason for that is backup to BD in case of hard drive failure on my servers.
For the DVDs, I use a CQ of 18.5 and that gives me an average size of ~2GB.

I have a fairly large video projection screen and I have no problem with the quality of the converted video. And I always have the original BD to view if desired.