I have a question about two different problems.

First, I imported a .mp4 video file into kdenlive. However, the program treated it like an audio format and wouldn't show the video. To try to get around this problem, I right-clicked the file and transcoded it to .mkv format, which worked beautifully.

I edited the video and went to render it to .mp4 format. This is where I encountered the second problem:

The rendering immediately crashed with the following Error log:

[mp3 @ 0000000005fc3f00] Estimating duration from bitrate, this may be inaccurate [mp3 @ 0000000009400a00] Estimating duration from bitrate, this may be inaccurate
[mp4 @ 000000000e829040] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead. [mp4 @ 000000000e829040] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead. Current Frame: 26, percentage: 0
[swscaler @ 0000000036266780] Warning: data is not aligned! This can lead to a speed loss Current Frame: 57, percentage: 0

I tried changing the output format to every possible option. I even tried to make a custom profile and rendering to .mkv format, but to no avail.
This is the first time that I've had a rendering issue, and the only thing that is different this time is that I used .mkv files in my edit, so I have to assume that that is the issue.

Any ideas on how I can solve my problem? Being able to render the edit as-is would be ideal, but even if there is a way to make the original .mp4 video files show up in the editor, that would also be helpful.

Thank you in advance if you can help me!

I found out that the source of the problem was not the .mkv files, but a .mov file with a transparent background. changing the format solved the problem. The issue of the .mp4 video showing up only as audio is still a mystery, but at least that can be worked around