Videos can be corrupted, or for other technical reasons (that we'll go in detail later) videos can't mix together without affecting the final product video or audio speed.
The software can be acting unexpectedly, or lack a feature you need.
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Let's say we have 2 videos, one you shoot on your phone and another on a profesional camera
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Because both videos have different settings, when you mix them in olive they will distort in some way, kind of like this:
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This happens because all video editors like olive asume all videos have the same settings. It can't work with different settings so the program stretches the audio 1 or video 1 to fit audio 2 or video 2
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We can use a program called handbrake to make all of our videos have the same settings and avoid audio or video stretching