I just used ffmpeg to convert a video file's container from .mkv to mp4 (just changed the container; didn't re-encode). The resulting mp4 vid plays well on QuickTime and am very pleased with the result. However, it wouldn't play in either Quick Look or iTunes.
In Quick Look as well as in iTunes, I am able to just move the play pointer up and down the slider manually but it just shows stills from the video. This is very frustrating as I was hoping to be able to add the video to my iTunes library! Any reason why this would happen?
Oh and if it helps, the codecs are H.264/AC3. Should that matter? A similar question elsewhere was closed with the accepted answer suggesting that the video be re-encoded. I really, really don't want to do down that road if there's ANY way to skirt that. I just want to change the container which is way faster than a full-blown re-encoding!
Best Answer
Conversion by QuickTime Player
QuickTime Player may be swiftly converting the file on opening using OS X's new AVFoundation. This would explain why it can play the file but not QuickLook or iTunes.
It is likely the movie is not in an ideal format for QuickTime Player on OS X 10.9, thus the conversion. With OS X 10.9, Apple dropped native support for many video formats and containers. Where possible legacy formats are converted on opening.
Supported MPEG-4
You may have a valid MPEG-4 container but the contents are not natively supported without conversion.
Have you confirmed the movie's encoding using the Finder's Get Info panel?
Re-Encoding
It is highly likely you will need to re-encode the movie, as suggested in MP4 movie does play in QuickTime but not in iTunes, if you want iTunes for playback.
This questions suggests a slightly different set of flags for
ffmpegto gain iTunes support, Convert a bunch of MKV files to MP4 to read them in iTunes:Alternatives to iTunes
If you wish to avoid re-encoding to gain iTunes support, consider looking for alternatives to iTunes. VLC and XMBC are both worthy alternatives; they both handle a wide range of video formats.