I sat through the complete Dog Star Man (4+ hours) in a museum in 1974. I dozed off quite frequently, but only for a couple seconds at a time. There didn't seem to be much sense trying to think the movie through, so I just sort of let it happen. When the lights came on, I decided this much-heralded avant-garde film wasn't anything special, only a little overlong.
I had to walk a mile back home, and it was midnight. In the twenty minutes it took to make this journey, the entire film ran through my head again, at lightning speed. I wasn't doing any drugs - yet the whole street around me seemed shot through with flickering light and overlapping images from this movie.
Back around 1960, neurobiologists had begun speculating that the human brain actually remembers every sensation we experience. Brackhage seems to have taken this seriously. Some of the images in DSM are only a single frame; but despite the "24 frames per second" rule of film-perception theory, one notes these single-frame images and remembers them anyway.
The bad news is that this is probably an historical footnote. The likelihood of seeing DSM in a theatrical setting grows dimmer every day. But there's absolutely no point of watching this in any video format whatsoever. In even the highest definition video format, a "frame" is constituted by overlapping runs of pixels in the process of moving from one image to the next. The presentation of a single-frame image such as I have noted above is physically impossible in video.
There are many other reasons why no video format could possible present this film adequately, but this is definitive. DSM works because light reflected from a screen can imprint a single image, however fleeting, onto our neurons. Video cannot do this, I'm sorry.
However, because Brakhage was a visual artist - not a dramatist, not a storyteller, but really the maker of paintings-in-motion - art museums will likely preserve this film - as film - for future generations. Some of these have quite adequate theaters for film projection. If you can make your way to one when this film is shown there, do so. Even if you hate it, you will not regret it. And you will certainly learn something new about the universe.