Is there any difference between .mkv and .mp4 when using HEVC (x265)?

[VG Docs]

As far as I've always understood it, there've never been any real differences between file extensions outside of compatibility. I've always been told that it's just a container with practically no differences and the main differences lie in the encoder (like HEVC). 

My uncle was told that it's not "True" 4k if it's .mp4 however. I don't know where he got this information but I just wanted to make sure I'm not out of the loop here (or am, if I am). 

Anyway - is there any difference between .mkv and .mp4 of the SAME HEVC video at 4k?

[LienusLateTips]

Nope, it's just a container.

[DrMikeNZ]

mkv and mp4 containers both can have x265 video. If the same video is encoded at the same bitrate with the same codec, then they will be the same.

[VG Docs]

1 minute ago, JDE said:

Nope, it's just a container.

Alright, thanks. Figured it was just online silliness or something but I just wanted to be sure I wasn't somehow missing out on info.

[.spider.]

There will be some minor file size differences due to container overhead.

[LAwLz]

Like everyone else have said, mp4 and MKV are just containers. If you put a HEVC video inside an MKV file then it will look the same as if you were to put it in an mp4 file, since the video is the same.

 

What will differ however is what the container supports. MKV will accept almost anything you throw at it, while mp4 has a lot of restrictions on what you can put in it.