Converting between .mkv .mov and .mp4

Should I ask an easier question (that I don't need the answer for)?

Your question is less than precise, audio compression format has not been stated, you have not indicated if source MKV file contains additional data such as chapters that you may wish to keep, and no specific "conditions" have been place on your playback requirements. In short, you seem to be familiar with the basic non-transcoding options available but can't seem to decide which option is best for your specific needs and workflow which you have yet to state.

I can change the file extension in Finder to .mp4 and they seem to then more or less behave as .mp4 files... Are they actually .mp4, or QT doesn't care and just opens them anyway?

They are not actually MP4 containers. However, if the video is compressed as MPEG-4 or H.264 and the audio is AAC, then most applications will play and/or process the files as MP4 files unless programmed not to do so. If you want the MPEG-4/H.264 video and AAC audio data in a real MP4 container, then use an application having a "Save As..." MP4 option (e.g., MPEG Streamclip) or use an app offering an video and audio "Passthrough" option to the MP4 container (e.g., the QT 7 Pro "Movie to MPEG-4" option).

If the MKV file contains MPEG-4/H.264 video, AAC audio and extraneous tracks such as AC3 audio and/or a chapter track, then using the QT 7 Pro or MPEG Streamclip "Save As..." option can save all of these tracks to a "real" MOV file container. Then, if your prefer (and the video is H.264), an app like Subler can re-mux the data to a real "M4V" file container if your work flow is targeting iTunes, mobile device (iPod Touch, iPhone, or iPad) or TV playback/management.

What is the best method of handling these files for widest usage on multiple devices?

The best method depends on what you are actually doing with the files, as well as, the software and hardware involved. Most QT based applications will play the content the same whether it is the data is in the MKV, MOV, MP4, or M4V file container—as long as the application you want to use supports the file container. (E.g., QT 7 requires external MKV support while iTunes, mobile devices, and TV will balk at the MKV file extension.)

I have read up as much as I can on the file formats but no-where does it say what OSX is actually doing when I change the extension.

OS X is not doing anything. It is the individual app you are using with the file and how it is programmed that determines if or how the file plays. If I take a "muxed" MPEG-2/AC3 VOB file and try to play it in the QT X player, it will refuse. If I have the QT MPEG-2 Playback component installed on my system and play the VOB file then I will be able to see the video but not hear the audio unles I have also installed a supplemental AC3 audio codec component. On the other hand, MPEG Streamclip will play the same file (both the video and the audio) with just the QT MPEG-2 Playback component installed. However, If I take the original VOB file and simply change the extension to MPG or TS, then the file should play in the QT X player.

Again, most media player only look at the file extension. As long as the compressed data is compatible with that extension, then it is usually happy. Older apps like QT 7 often check the internal file headers against the data contained to ensure the two are compatible. Newer apps like QT X tend to look at file extensions first and then check the compressed data to see if it is compatible. However, if the app is not programmed to recognize/support file extension, then processing halts at this point whether or not the content is actually playable. For this and the above mentioned reasons, I normally opt to play compressed data in "real" file containers of a specific compatible type rather than merely changing the extensions even though it takes a bit longer to copy the compressed data to the new file container than it does to change the extension. But once again, this is just my personal preference.

Am I right in wanting them to be .mp4 files?

Once again, this may depend on the data contained in the original MKV file and what you wish to keep. I target my content for iTunes management and iPhone, iPad and TV playback. As such, I use a universal 720p H.264/AAC/AC3/Chaptered M4V anamorphic compression since some apps/devices can use all of the data and others simply ignore what they cannot play. In this case, an MP4 file container would probably be inappropriate since if I change the extension to MP4, many apps would refuse the open/play the file due to the incompatible data and trying to copy the data to a "real" MP4 file would automatically strip the incompatible data tracks from the target file container. Thus, the "best" option, method, or workflow for you may or may not be the same as the "best" one for me. In fact, it is quite likely that what is "best" may change depending on final use of the file which may change from one project or day to another.

I didn't state the audio format(s) because it has rarely been an issue, if it fails it fails at the first hurdle. The container.

Non-AAC audio will likely fail to load/play if the MKV Extension is changed at the Finder Level. Using MPEG Streamclip to move the compressed data to a "real" MP4 file container will normally strip the audio from the final file. If you wish to retain the audio, use the QT 7 Pro "Movie to MPEG-4" option, use video passthrough, and transcode the audio to AAC.

Most of the .mkv files have aac audio, but not all. Chapters are irrelevant, never having found any nor thought them useful.

This is a user preference. I prefer to keep the original chapter markers for apps that use them rather than falling back on the defaulted markers added by some device players.

I am playing the files on several Macs, 2 PCs, an iPhone, iPod Touch, iPad 2 and possibly future Android devices. There are even 2 TVs which seem to be stuck with only reading avi.

Macs, iPhones, iPod Touch, and iPad will play H.264/AAC compressed data natively in MOV, MP4, or M4v file containers. PCs and Android playback will depend on the compatibility of the player app used on the device. Macs will play H.264 with any audio supported by your Mac codec component configuration in the MOV file container.

My main target however is a PS3, which has turned out to be the most flexible media device in the house but does object to some files for indeterminant reasons. I will need to do comprehensive testing to find exactly what it is it doesn't like. Mostly it is good, once you update the system.

Do not own a PS3 but believe it is supossed to be compatible iTunes and mobile device supported formats. Again, the file container of choice would depend on the content you wish to include in the file. If you want to include AC3 DD5.1 sourround soud audio, I would normally recommend the MV4 or MOV containers.

The secondary target is iTunes so that I can get the files onto my iPod Touch and iPhone. I'm sort of used to that level of Apple devices (and I presume AppleTV) "Just not working" unless it suits Apple. So I restrict my viewing to mp4 files of my own creation or mkv files so over the top in size that recompression does little to degrade them.

Again, the M4V file container with H.264/AAC with or without AC3 surround audio, alternative AAC audio, and/or chapters is usually the preferred norm. If you plan to use a "universal" file format, then the display dimensions, frame rate, profile, and level for encodes may depend on the specific devices involved. I.e., that is why I limit my files to 720p30 Main Profile Level 3.1 to High Profile Level 4.0 compression and rarely use even half (more commonly only about a quarter to a third) of the video data rates allowed with these settings.

XBMC and other Media Server software seem, like VLC to be pretty tolerant, and whilst I haven't yet built myself a Media Server, it is on my longer term To-Do list.

I use iTunes for in-house media server software to TV and mobile devices with Air Video as my primary server software externally via the internet to mobile devices when away from home. Both access the same Promise Pegasus R6 12 TB RAID storage device. (Have moved most of my content from an old Drobo Pro RAID and am in the process of upgrading the current 16 TB unit to 24 TBs as individual drives fail for the storage of raw video footage.)

The h264 should pass straight through in a simple QT resave? Same if it has AAC audio?

If the source MKV file is playback compatible with your system's current codec component configuration, then the QT 7 Pro or MPEG Streamclip "Save As..." option can copy the data in the MKV file directly to a new MOV file container without transcoding/recompressing any of the data. Unfortunately, the QT X player is a bit more iffy. Basically, Apple has combined the "Save, Export, and Save As..." options in to a single menu option. The result is that sometimes the app will recompress the data and at other times it may not—dependent on a numbe of variables.)

If the MKV file contains H.264 video and AAC audio, then the MPEG Streamclip "Save As..." option allows you to select either MOV or MP4 as the target file container. If the MKV file contains H.264 video but the audio is not AAC but is still export-compatible with the QT 7 Pro app, then you can use the QT 7 Pro "Movie to MPEG-4" Export option to pass the H.264 video unchanged to a new MP4 file container while simultaneously coverting the audio to AAC. Since you still have not stated what non-AAC formats are included in some of your MKV files, I cannot tell at this point if this is a viable workflow for you.

That covers most cases. I'm still not a 100% clear on tghe real differences between .mov and .mp4 containers and how much it really matters in the scheme of things. .mp4 seems to the go, does .mov cause a problem? If so how and how best to rectify that?

The containers are different. They have different internal identifiers, features, capabilities, and sometimes limitations. CDs, DVDs, and BDs are all different types of optical media but each has different capacities, ratings, and features that determine how they can be used, what kind of media can be recoded on it, and what kind of a device must be used for playback. MP4 containers are very limited. Thay can only conatain MPEG-4 (MPEG-4/H.264) video and MPEG-4 (AAC) audio. M4V file containers are less limited and may typically contain H.264 video, AAC and/or AC3 audio, and chapter tracks. MOV file containers are generic and can hold up to 99 tracks of audio, video, image, text, 'tween, sprite, etc. data that is compatible with the system on which it was created. As to MOV files causing a problem—yes and no, depending on how you use it. Put "muxed" MPEG-2 data in an MOV file in an MOV file container and it will play normally in the QT 7 player (with the QT MPEG-2 component installed)—i.e., no problem. But try to play the same file in the QT X player and it will tell you that you are missing a codec component—a definite problem since you tried to play playable content in a container the media player did not expect to contain that particular form of compression. As to fixing aproblem. I would be better able to answer that if I knoew what specific problem you were referring to here.

This is why I keep harping about knowing which player is to be used, what audio and video compression format is being used and what container is to be used. And we have not even gotten around to checking the H.264 settings. QT based players are standards conscious. Each Profile and level combination tells the player the max macroblock decoding rate, number of macroblocks allowed per frame, the maximum video data rate allowed, the highest useable resolution @ the highest frame rate, what features are supported by profile, etc. Unfortunately, some third-party venders sometimes hybridize these settings which can make the files unplayable in QT apps but they may still play on other players which do not check on or trap on the use of non-standard settings.

BTW I did a quick hunt around on h265 and can't see what Apple is doing. Giving it a miss like it did with Bluray?

Apple is not known for embracing such technology quickly—especially since they are still drafting and reviewing drafted standards. (I believe DivX released a draft version on the 15th of this month.) The current evolution of QT X will probably take another 5-7 years and Apple will have to design hardware capable of handling 4K and 8K if anyone is actually going to put it to use on future Mac systems. The development of mobile devices have, for the most part, only been supporting 1080p resolutions for a relatively short period and jumping to 8K would represent something of a quantum leap at the consumer level.

I know very little of file extension and format, I use Handbrake and AppGeeker all the time to convert my videos.

MP4 may be the most widely used file extension amongst mobile devices, players and desk applications.

How to Convert MKV to MP4 on Mac/PC Flawlessly

I generally have pretty good results with that.

Hi, I know less about the extension, but I think the most important thing is I get the format I want at last. Usually I do the video conversion with the software:https://itunes.apple.com/us/app/video-mate/id592736614?ls=1&mt=12. It can convert between .mov, .mkv and .mp4 smoothly. And it can also do simple video editing work and output settings. So far, it is quite helpful to me. You can have a try.

Today, converting MKV to MOV or MP4 becomes simpler and simpler, since there are many available MKV to MOV or MP4 Converters online. But most of them only can either convert MKV to MOV or MP4 with low output quality or doesn't support converting MKV to MOV or MP4 with subtitles. Even the converted MOV or MP4 files are incompatible with the desire devices like iPhone, iPod, iPad, etc. So a lot of people are still looking everywhere for the one which is both professional and economical.

Before going to download or purchase, find out the best MKV to MOV or MP4 converter.

I use iDealshare VideoGo to convert between .mkv .mov and .mp4 with the original video format and fast conversion speed.

It can convert MKV to MOV, convert MKV to MP4, convert MP4 to MKV, convert MOV to MKV, convert MOV to MP4, convert MP4 to MOV.

It even can convert among MKV, AVI, WMV, MP4, MOV, WTV, OGV, FLV, SWF, VOB, WebM, ProRes, DV, 3GP, etc video format.

I've tried many different converters and most of them lack design or functionality. Since I watch a lot of movies on my iPad while travelling abroad, I find it challenging finding good movies for it in the right format. A week ago, I found a magical app called WALTR. It supports MKV, AVI, MOV, MP4, M4V, 3GP, WMV and many other video formats, so it can easily convert MKVs to MOVs. It's is ridiculously simple. Just drag-and-drop and it's on your iPhone, iPad or iPod. You can find a quick guide by following this link - https://softorino.com/waltr/windows-guides/how-download-mkv-video-ipad-pro-windo ws