I have created some DNXHD files to lower the stress on CPU time while editing.
The footage is in Full HD. Unfortunately it seems that is loaded in 480p.
Also the width is 4:3 with black borders left and right instead of 16:9
Does it make sense to use filters to make it fit?
The H264 files are being displayed correctly.
DNxHD is quite strict with settings and its easy that the result is not as expected. Try using DNxHR, much more convenient and faster to use. By now DNxHR has completely replaced the old DNxHD. You can find it under the container mov, in various quality presets.
Thank you.
Im in the render dialog:
I have chosen FFMPEG and .mov
Then I click on the wrench tool icon at video.
But there I cant see anything about DNxHR
The .mov DNxHR formats were added after the 10/31/2020 tar/pkg distributions. So you can either add these formats manually for usage or use the latest AppImage (which is just new so not been subjected to a lot of usage yet). It is at:
https://cinelerra-gg.org/download/testing/
either cin_for_newer_distros.AppImage (or the older one if your O/S is older).
The DNxHR formats can be put into the bin/ffmpeg/video subdirectory of Cinelerra for usage and will show up as an option the next time you start Cinelerra. If you want these formats, someone can supply a zip file to send.
Thank you for the information!
Im running LXDE and this Environment doesnt offer to open appimage just by executing.
I will try it on a virtual machine tomorrow.
Attached is a tar/gzip file of the DNxHR formats which both Andrea and Andrew have provided for the checkin and tested for very good reasons.
The advantage of using these mezzanine codecs is that it preserves all the information in the original file throughout the editing process. In addition, they are uncompressed codecs and therefore not overly CPU-intensive. They are indispensable for high level works of Color Correction, denoise, mask and Chroma Key, where the compression artifacts do not allow good results (Andrea quote).
dnxhr.tar.gz
Oops, there are also 2 audio formats to go along and I have attached here. They will need to be copied to {your cinelerra directory}/bin/ffmpeg/audio
dnxhr_audio.tar
That works well 
Thank you very much!
Note for the problem with AppImage.
For Arch linux you have to install the libappimage library, I dont know for other distributions. Then you have to give execution permission to the AppImage file, for example enter the directory where the appimage is and:
chmod +x cin_for_newer_distros.AppImage
and then:
./cin_for_newer_distros.AppImag (Oppure un semplice doppio click sullicona)
Since appimage should become the way to propose CinGG in the future, if you can test and point out errors and problems its a big favor.