user20059: I need to send a short video clip (30 seconds) to a client of mine, the video is 3840 × 2160 resolution.
The client is using some cheap, 4k TV and he is using a USB to play the video which only supports JPEG, MP3, MKV.
Is there any way to export/convert the video (.mov) to .mkv while keeping the same resolution? (3840x2160), I tried some softwares but they reduced the resoultion to Full HD.
I have all of Adobe CC programs if that helps.
Thank you.

user17716: 
Is there any way to export/convert the video (.mov) to .mkv while keeping the same resolution?

Yes. It's called ffmpeg. It's an advanced high level command line tool for basically all your video conversion needs.
Download the tool from here. You'll need to unpack it to any desired location. You can either add the bin folder to path or copy your .mov video file into the bin folder itself.
Then open the command prompt and type in the following code.
ffmpeg -i "filename.mov" "filename.mkv"

The video should now convert to .mkv format preserving the resolution.
Note:
.mkv is a container format. Which means the video file can have any codec, including those not supported by TV. So its useful to know which codecs the TV supports. By default, ffmpeg uses libx264, which should work in most devices. 
Also check this question, about a similar problem I had with my TV. It should make things a lot more clear to you.
PS: As mentioned in the other answer, Handbrake should also work. Its the graphical tool based on ffmpeg.

20059: <p>I need to send a short video clip (30 seconds) to a client of mine, the video is 3840 × 2160 resolution.
The client is using some <strong>cheap</strong>, 4k TV and he is using a USB to play the video which only supports JPEG, MP3, <strong>MKV</strong>.</p>

<p>Is there any way to export/convert the video (.mov) to .mkv while keeping the same resolution? (3840x2160), I tried some softwares but they reduced the resoultion to Full HD.</p>

<p>I have all of Adobe CC programs if that helps.</p>

<p>Thank you.</p>
 17716: <blockquote>
  <p>Is there any way to export/convert the video (.mov) to .mkv while keeping the same resolution?</p>
</blockquote>

<p>Yes. It's called <a href="https://www.ffmpeg.org/" rel="nofollow noreferrer">ffmpeg</a>. It's an advanced high level command line tool for basically all your video conversion needs.</p>

<p>Download the tool from <a href="https://www.ffmpeg.org/download.html" rel="nofollow noreferrer">here</a>. You'll need to unpack it to any desired location. You can either add the bin folder to path or copy your .mov video file into the bin folder itself.</p>

<p>Then open the command prompt and type in the following code.</p>

<pre><code>ffmpeg -i "filename.mov" "filename.mkv"
</code></pre>

<p>The video should now convert to .mkv format preserving the resolution.</p>

<h2>Note:</h2>

<p>.mkv is a container format. Which means the video file can have any codec, including those not supported by TV. So its useful to know which codecs the TV supports. By default, ffmpeg uses libx264, which should work in most devices. </p>

<p>Also <a href="https://video.stackexchange.com/questions/20569/mkv-file-not-playing-in-hevc-h-265-supported-player">check this question</a>, about a similar problem I had with my TV. It should make things a lot more clear to you.</p>

<p>PS: As mentioned in the other answer, Handbrake should also work. Its the graphical tool based on ffmpeg.</p>
