Ripped MKV Hash Differences

[1wayjonny]

I briefly posted before about this got a high level answer but wanted to revisit as I still see difference in pulled MKV via checksums. Specifically two scenarios both report inconsistent results.

Being that the drives can have errors but more importantly oily/dirty disc from the factory I wanted to ensure the rips where ok. I understand that MakeMKV does a hash table check which is great.

The questions is around the pulled mkv's checksum, I can rip from a disc 10x and that movie will all have different checksums every time but each movie plays fine, no issues.

So I also did this test across 10+ movies that were first backed up to the hard drive, eliminating disc ripping issues. Then I proceed to rip the same MKV with the same audio, subtitles, etc. and even when creating MKV's from a hard disc all the MKV's have different checksums.

When I posted a while back about, I remember Mike says they should be the same as long the user is ripping the same MKV, no modifications between the MKV. (I.E. removing tracks, subtitles).

What could MakeMKV doing to each file that makes it unique where the checksums just do not match what so ever, no matter the rip? The hash table does not change for the files on the disc, the program uses it for reference. So curious to why we get different MKV's bit2bit comparison. Is the program adding random data per MKV creation?

If I miss understood something, I would like to clear this to ensure rips are working well and we all have a good understanding of what to expect.

I think Mike will have to answer this one but appreciate the clarity.

[Woodstock]

The header of the MKV file has the date/time it was ripped. Rip 10 times, you'll have 10 different time stamps, which will change the checksum AND any hash check you do.

[jayper]

EDIT: There you have it. Woodstock beat me to it by seconds.

This is only a theory, and I am far from an authority but one idea:

MakeMKV sets an encoded date and time for each MKV created. Even if everything else is the same in the file, the encode date and time are going to be different and thus changing the hashes.

Could that be it?

[1wayjonny]

Hi guys, I really appreciate the answer and clarity, super simple answer. I did not know the date/time is included and it makes complete sense why they do not match.

I will need to adjust my understanding/expectations to just confirm when its backed up against the hashtable.

Cheers!

[Woodstock]

Ideally, you would want something that could do the comparison on the tracks within the MKV container. THOSE should be the same.

[DeadPixel]

Yes, they will be. You can use a program called gMKVExtractGUI or if your into command line use mkvextract.exe that is part of mkvtoolnix. This can extract the individual tracks from the container (.mkv).

If you hash those and compare they will be identical.