I have a .mov file that won't play in Quicktime - do I need to download a decoder?

Found out via Movie Inspector that these .mov files have DVC Pro HD Codec - which I believe has to do with Avid Editing software? Anyhow, I need to find out what I need to download in able to see these video files? Do I have to purchase a decoder of some kind? Hopefully not? Is there any other way to view these files on my imac? I am running OS X Mountain Lion v10.8.5 and have both Quicktime 10 and 7 installed.

QT includes DV/DVCPRO-25/50 family of codec components as part of the basic Mac OS X system package. Unfortunately the DCVPRO HD family are considered "pro" editing codecs and are not included. Normaly the "Pro" codecs are installed automatically by "Pro" editing software such as the Avid editing package you already mentioned or Apple's Final Cut Pro software. Unfortunately, most of the codecs in such packages are not sold for installation independent of "pre" editing software. For instance, Apple does have a "Pro" codec download package but it normally can't be installed by the included installer unless you already have the associated editing software installed.

Would you suggest I put them through something like Toast and try to convert it to an .mp4 or .mov file again?

Right idea—wrong application. You still need to be able to acces the a "pro" set of codec components. Basically you can purchase and install FCP X ($299.99), Motion 5 ($49.99), or Compressor 4 ($49.99) to gain access to the ProApps QT Codecs package. Once you install any of these apps, you can run the Software Update utility to download and install the "Pro" codecs package as described in SUPPORT ARTICLE HT4714. Once the codecs are installed as part of your system's QT codec component configuration, they will be available to all media apps that can access your system's codec configuration—e.g., QT 7, QT 7 Pro, QT X, iMovie, GarageBand, MPEG Streamclip, etc. Since you mentioned clients, I assume you are providing a profesional service and might find $50 a fair investment for access to the entire ProApps QT codecs package which also includes other professional editing codec families. In any case, this workflow does provide a low-cost, easy way to leagally install the "pro" codecs on your system(s).

P.S.

You can read DOWNLOAD ARTICLE DL1396 to see which "pro" codec families are included in the ProApps QT codecs package. This may help you better evaluate whether or not you wish to go this route.

I am having the same problem as described in this question. If I buy Motion 5 will it allow me to then use the .mov clips in iMovie, or do I need final cut?

I am having the same problem as described in this question. If I buy Motion 5 will it allow me to then use the .mov clips in iMovie, or do I need final cut?

Can't say for sure based on personal experience. My codecs were initially installed under FCP Suite v6 and updated later. Believe purchase/use of any of the video editing/conversion programs listed under Apple's "Professional Applications" heading allow installation of separate "Pro" codecs download. (I.e., my older version of Motion stopped working several Mac OS X system upgrades ago and I never upgraded/purchased a current version.) Maybe a current Motion 5 user can provide a more definitive answer here.

From many examples, we can conclude that MOV files shot by digital camera, downloaded online, or obtained from others encoded with QuickTime incompatible video or audio codec, etc are not compatible with QuickTime. In fact, only MOV file encoded with MPEG-4 or H.264 video and AAC audio is supported by QuickTime. If your MOV files are encoded with other video or audio codecs, QuickTime will refuse to play them.

After a quick search, I found a solution. I recommend this way to my friend who had this issue too and then the issue was solved.