Author Topic: [SOLVED] Why do MKV files take so long to load?  (Read 5053 times)

zakafreakarama

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[SOLVED] Why do MKV files take so long to load?
« on: May 03, 2015, 05:30:30 PM »
This may be a stupid question, but Avidemux is the only video editor that needs so much time to load Matroska files (I'm thinking BD remux mainly; some files need as much as 20 min to load), whereas other editors like KDEnlive and OpenShot load them instantly. That being said, Avidemux fills my needs much better than those two, and it hurts that it underperforms in this particular issue. Needless to say, MP4 files using the same codecs load in no time. Can anyone please explain this to me?

This is out of curiosity, so please do not take this post as criticism. It is not.

Thanks a lot, guys.  :P
« Last Edit: May 05, 2015, 08:07:52 AM by zakafreakarama »

mean

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Re: Why do MKV files take so long to load?
« Reply #1 on: May 04, 2015, 05:54:58 AM »
It rederives image type (i/p/b / idr) to make sure it has the correct type, that implies partial decoding of the file

Jan Gruuthuse

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Re: Why do MKV files take so long to load?
« Reply #2 on: May 04, 2015, 06:02:52 AM »
partly directly related to cpu/gpu processing power, hard disc read/write speed and available memory and most likely the OS too.

zakafreakarama

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Re: Why do MKV files take so long to load?
« Reply #3 on: May 04, 2015, 12:09:41 PM »
I can understand that. What I don't get is why some files, while carrying the same codecs and having similar sizes, take much longer to load. I recently downloaded 2 BDrips of the same movie to compare and keep the best one to reencode to DVD. Both are  +-8GB MKV files with H.264 video at full HD resolution, 24 fps, plus a DTS audio track and a few subtitle tracks. One of them carries an extra AC3 audio track. This one loads in around 3 min. The other one, with only 1 audio track, needs up to 15' (!) to load. Tried to remux it with MKVtoolNix. That did nothing. On the other hand, if I just keep the video and remux to the MP4 container, the file loads in no time in Avidemux. That is probably what I'll do when working with HD content in Avidemux: keep the audio tracks aside and mux the video stream into the MP4 container, which is clarly easier to work with using this software.

Thanks for your help.

Jan Gruuthuse

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Re: Why do MKV files take so long to load?
« Reply #4 on: May 04, 2015, 12:58:16 PM »
.mkv is a box, 8GB is the size of the box. This says nothing about the video/audio content: compression. see details here: http://en.wikipedia.org/wiki/H.264/MPEG-4_AVC
decoding maybe more or less complex and takes more or less decoding time. This goes far beyond my user experience. To many factors come into play to understand why these differences are there.

mean

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Re: Why do MKV files take so long to load?
« Reply #5 on: May 04, 2015, 01:06:33 PM »
Basically the index in mp4 can be generally trusted
The ones in mkv not really, so avidemux only rederives mkv and not mp4, unless it finds inconsistencies

zakafreakarama

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Re: Why do MKV files take so long to load?
« Reply #6 on: May 05, 2015, 08:07:30 AM »
OK, got it.
Thanks a lot!  :)