Seems that AnimConvert, the above program, cant convert AVI directly to ANIM5, it needs to demux the AVI into IFF frames first. And in the AVI files that it supports there are some bad options, like Cinepak for example (I was expecting at least HuffyUV), and worse, it doesnt convert MPEG2 or MP4.
But for those there is ffmpeg, which I "think", the versions for AmigaOS should handle well. It can be found on aminet together with FFMPEG-Gui.
And with some commercial programs for AmigaOS, is possible to put sound in a ANIM5. But I found for my surprise, that the sound in these ANIM5 are not builtin, interleaved to the video, its fake, and thus get out of sync very easily. They depends on the 8svx file that comes together with the ANIM5 file, at least everything that I saw.
Only CDXL and AVI4HV are interleaved on Amiga.