Export and transcode functions are available in the video actions underneath the listing of events (see #6 on the getting started page.)
Version 2.5 of Focus introduced new export and transcode functionality to work around issues with some of the videos that were being created by the car and the macOS decoder. For more details, see the blog post about the issue.
Note that both exporting and transcoding can be lengthy operations, especially on older machines.
The export function will export the current view shown in the main window (either a combination of the four cameras, or one particular camera.) The export size can be chosen in the save dialog after the export button is clicked.
The export function will attempt to export the selected time ranges of the cameras in the main window. This can be either the entire event, or the selected time ranges in the scrubber, if there are any. Sometimes, video coming from the car is written out in a corrupted state and cannot be decoded by the exporter. This has become more common in recent versions of the car's software. It usually shows up in the viewer as a flash, or a black frame. Sometimes, certain camera angles can fail to write out at all.
When the exporter comes upon a corrupt video, you will see the progress dialog reset and switch to "Transcoding..." This is expected behavior. Focus will transcode the videos before proceeding with the export, and when the video finishes exporting, the transcoded videos will be automatically removed so that extra disk space is not consumed.
The transcode function takes the existing video and transcodes it to another format. Along the way, any corrupt frames are removed so that any future operations proceed smoothly. The original videos are kept, stored in a new event folder with it's previous name suffixed with "-original". Once transcoding is complete, you may remove the "-original" folder if you no longer want to keep it around. The new transcoded video will play normally, both in Focus and in the car.
Transcoding writes the videos out using multi-pass HEVC encoding. When the transcode button is clicked, you have the option of choosing the quality of the output video. The default settings provide quality approximating the original video, and will result in files that are typically around 10% smaller than the originals. You can also choose lower quality output settings, resulting in videos that can be around 75% smaller while retaining decent quality in most cases. This makes the transcode function good for archival purposes.