Never encode 2 movies at the same time

[Blackblades]

I was encoding 2 movies at the same time using 2 opening mkvtomp4s. The 1st time failed because the computer shut off in sleep mode which I forgot which is my fault. Then I did it the 2nd time it went slower then the 1st time, and after 9 hrs it was done just to find out both some how combined into each other. Where one movie would have 10-20mins of the other movie in the beginning. Didn't think they would combine if encode 2 at the same time so now I know.
Also why when I encoded a movie it took 3hrs and others took longer. Like the movie was 3gbs and it finish about the same size, and some others was 700mb like a mini hd and encoded it went to like 2gbs. I might have a theory about that though.

[jagabo]

The intermingled results are a bug in the particular to the program you used. Properly written software will not intermingle different videos no matter how many simultaneous instances you run. Would you expect a video encoding running in the background to screw up your Excel spreadsheets? So why should two video encodings screw up each others' picture? Stop using that software.

Slow speed could be an issue of over heating. A single conversion may not use 100 percent of your CPU leaving it running at full speed. Running two conversion at the same time may use 100 percent and cause the CPU speed throttle back to keep from over heating and burning itself up. This is a big problem with laptops because they usually have insufficient cooling. But it can happen with desktops too. Especially those with AMD processors that consume a lot more energy.

Another cause of slow speed would be a disk I/O bottleneck. But those usually only occur with uncompressed or losslessly compressed codecs.