When saving a selection of its frames to files like JPG, there appears to be a limit of 9,999 files maximum allowed. Why is it limited? In my little use of the feature, it seems this equates to only about 5 minutes of run time for a file.
Thanks!
This feature was never intended to dump whole movies. The total number of files must be limited to have a fixed number of digits to add to the filename. By the way, in case the output directory is located on a FAT32 filesystem, already the limit of 9,999 may be too high if the filename of the video is sufficiently long.
It might be useful to be able to dump every Nth frame or every keyframe however, not possible yet.
edit: To extend the time fitting into the max number of output files, select a video codec different than "Copy", add the "Resample FPS" video filter, configure it to reduce FPS to e.g. 1 fps (the lowest possible value) and enable filtered preview in Avidemux. Now "save selection as JPEG images" will save one image per second of video, enough for over 2.5 hours of run time.