Recently I started my video blog on YouTube. To shoot videos I use DJI Action 2 camcorder. It can record videos up to 4K@60 FPS. Obviously, resulting video files are heavy for editing and rendering. Are there solutions on Linux that help you to work with modern high definition video? The answer is yes and here is my approach.

Editing

To edit video I prefer Kdenlive. It’s a powerful open-source video editing software. The UI part is powered by KDE and QT technologies. Rendering and editing is based on melt framework. Kdenlive has interesting feature named proxy clips. Even the high-end CPUs will be brought down to the knees when you try to edit 4K video in real time. So instead of working with original files Kdenlive uses files with lower quality. My camcorder records these low-res files along with original ones. This drastically improves your editing experience. When you render your project the original files will be used.

Rendering

Looks like you cannot cheat physics and you have to wait for a long time until the project will be rendered on a weak laptop CPU. But it’s not true :) What if the rendering could be performed remotely on a more powerful machine? You just need an instance on some cloud provider such as AWS, GCP or Azure. Kdenlive can generate a script for melt command line utility. So you don’t need to install Kdenlive on a remote machine. And what about video files? I the beginning I decided to upload them using rsync but it would take several hours for my project. I had several hundreds of gigabytes. I started to think if it’s possible to mount my local directory on the remote machine. Fortunately, everything can be done with a couple of commands. You just need ssh and sshfs. Here are commands for Ubuntu:

  1. Install the ssh server.

  2. Run an sftp server on some port on the local machine:

cd <PATH THAT SHOULD BE MOUNTED ON THE REMOTE MACHINE>
ncat -l -p 34567 -e /usr/lib/openssh/sftp-server &
  1. Make a tunnel from the remote instance to the port on the local machine and run sshfs and bash. Make sure that pah exists on the remote host:
ssh -t -R 34568:localhost:34567 <USER@REMOTE HOST> "sshfs localhost: <LOCAL MOUNT POINT> -o directport=34568; bash"

After that all you need is to run melt <PATH TO SCRIPT>. One thing you should know that the script contains absolute paths to the video files. So you should either edit the script or use the same paths on both local and remote machines.

Results

Obviously you should have the fast enough internet connection otherwise it will be the bottleneck of the whole pipeline. I tried that trick with two Digital Ocean instances: 48 CPUs and 16 CPUs. I noticed that the more powerful instance doesn’t give you 3x boost performance. Looks like ffmpeg and encoders such as x265 don’t utilize all available CPUs. Anyway, using this approach with fast internet connection you will speed up video rendering.

References:

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