QuickTime Player will not play .mov file My QuickTime doesnt want to play a .mov file.  I tried to convert .mov to .mp4 format using cloud convert but it gave error message:

Converter error: oov atom not found . PCO11_059_RM.mov: Invalid data found when processing input.


I've got the latest OS X software, 10.11 El Capitan, which I'm assuming would give me the latest QuickTime Player.  Any clues?
Try VLC

Try playing the file using VLC. VLC tends to be able to play files and formats that do not work in QuickTime Player on the latest OS X.

Re-encode using VLC or Handbrake

If VLC works, then you can use VLC itself or a tool like Handbrake to re-encode the file to a format that works in QuickTime Player.

Many Formats in One

The mov file format is a wrapper and can represent many different media formats internally.

With the Finder, use Get Info on the mov file. What do you see in the More Info: section? As an example, in the screenshot below the movie is really a collection of photos with cross fades.