ImageJ cannot read Cinepak codec video files. Convert from Cinepak to popular video formats using FFmpeg.
Motion JPEG is widely-compatible with video players including ImageJ.
ffmpeg -i old.avi -c:v mjpeg -q:v 1 out.avi
Uncompressed AVI output file size could be a factor of 10 larger than the Cinepak version. By definition, every video player should be able to play uncompressed AVI–including ImageJ.
ffmpeg -i old.avi -c:v rawvideo out.avi
Lossless FFV1 preserves the original video quality with lossless compression. Many video players can handle FFV1 AVI video.
ffmpeg -i old.avi -c:v ffv1 out.avi
The advantage of using a PNG image stack comes in frame-by-frame analysis of the video.
You could also consider converting video to HDF5 using dmcutils/avi2hdf5.py for analysis purposes.
There are two plugins that attempt to address this for ImageJ:
But I found neither of them to work for me on the particular AVI Cinepak video I was given.