Occasionally, EditReady might become set as the default file handler for some types of video files. That means when you double-click on a file (like an MP4), it opens in EditReady instead of QuickTime Player.
To correct that, follow these steps.
Highlight any movie file in Finder.
Press Command-i on your keyboard.
In the Open with: section, select "QuickTime Player".
Click Change All...
Making QuickTime the default player
Errors During Conversion
Some issues may be caused by invalid output destinations. To test whether this is the case, try setting the Dest Folder option to your Desktop. You can also try moving your source media to your Desktop to rule out any external or network storage issues.
Transcoding directly from SD cards can be especially problematic, as SD cards can generate errors during the types of sustained reads from transcoding operations.
MXF, HDV (M2T), and AVCHD (MTS) Files
You can test whether your MXF or AVCHD/HDV (MTS/M2T) file is valid by trying to play it with the free video players like: