Thanks to Anthony and others who recommended Subler in the comments. Sometimes, you only need to copy the audio of a video. You can use the same command to copy the video in any format.
If you need to convert other video types to iOS compatible format, Handbrake works great for that. flac -c:v zmbv -compressionlevel:a 12 output.mkv Convert FMF to a DVD video format: fmfconv input.fmf ffmpeg. Converting a webm file with various audio and video codecs to an MP4 file with H.264 video and AAC audio.
On a side note, converting MKV to M4V isn’t necessary if you want to watch the movie directly on your computer, in that case, check out a handful of free MKV video players for Mac. The resulting M4V video can now be synced through iTunes to an iPad, iPhone, or iPod touch, played directly on an Apple TV, or watched on any other device or app that supports M4V. You’ll see a “Saving” progress but Subler works very quickly, you shouldn’t have to wait long for the repackage regardless of the origin MKV video size.