I will argue this notion, to a degree, with a channel known as RedLetterMedia.
The majority of their content consists of 45 to 1 hour and 45 minute videos where they sit and talk about crappy movies that they just watched previously, as well as brand new movies that they just saw in theaters. And most of their recent videos (at that length) in their series called "Half in the Bag" and "Best of the Worst" have between 200,000 and 400,000 views each.
That's a very particular fan-base, to be sure, but it definitely says something about how the attention span for long-form videos on Youtube has changed dramatically since 2005. Not to mention the millions of people who watch long-form Let's Play videos, which can last up to an hour or more as well.
These are also not movies: these are reviews of movies that involve a more friendly and an almost intimate style of conversation between like-minded people. It feels like you're spending time with these people and having fun riffing on scenes and characters you just experienced. So the engagement factor is much higher for longer periods than it might be if you were watching a regular film unfold over an hour or more. The dynamic is much different.
All I'm saying though, is that there are plenty of people who can and do watch really long videos. Whether or not they'll watch an amateur movie on Youtube is a different story. Cause these guys have made movies too, but I don't think they've been as successful as their review shows.
I can rebut this one pretty easily, and with personal experience on the matter.
Let's take a look at my girlfriend. She spends a lot of time on YouTube watching videos that sometime go on for about 3 hours. What are they? Well they are GameGrumps Let's Plays. But let's break down some psychology here.
Does my girlfriend like video games? Nope, she couldn't care less actually. So why would she sit around for half the day watching two guys play video games? Well she finds them personally entertaining. The actual content the video couldn't matter less to her. She just wants to hear their jokes and stories.
Strangely every fan of GameGrumps I meet (because I have a strange personal vendetta against them) I question the viewer why they watch the videos (as in my opinion.. and fact of how quickly they lose, they suck at playing video games) and 9/10 it's because they like the jokes and stories. 1/10 it's because they are playing some new Nintendo game that the person wants.
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Can this apply to your movie reviewers? Most certainly! In fact this can apply completely to your movie reviewers because they are basically the same thing! AngeryJoe for example is a guy who does nothing but critique games for their crappy mechanics. People enjoy hearing criticism for something they didn't work on. I'm also sure these guys have some funny comments from time to time.
A fact that one of the series you referenced is called "Best of the Worst" is point and case to this psychological indulgence that people like. People who don't even like movies most likely watch these people.
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We can get historical about this, Indy Mogul was HUGE! Do you think all their viewers wanted to be filmmakers? Of course not, they just liked the creators and their jokes. Same reason for around half of FilmRiot's fan base, the riffs between the two brothers and their sister is the entire point of watching for some people (most likely more than you'd think).
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Lastly to drive in this point even more. Take GameGrumps and do some searching for Best of videos, and you'll find compilations that take the best from each game walkthrough and just put all the funny parts into a 1 - 3 hour video.
To prove the point I attempted the same with RedLetterMedia and was proud to find the same results. People are in this for the jokes honestly. I'll bet only a small majority of their fanbase are actually movie buffs, the same as I've found is true majority of GameGrumps fans aren't gamers.
------------------------------------------------ TO THE POINT ALREADY SKY!
This is a different breed of content... You are in the film side of YouTube, a area that's SUPER hard to get people to watch your indie SHORTS. An even slimmer than that already extremely small viewer base is going to click on your video, a smaller number than that is going to get 30 minutes in, and the number keeps dropping every ten minutes.
Honestly, you have to be real with yourself because false expectations of this industry will crush you before you can even start.
Never rely on "going viral" cause it's not going to happen.
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Kinda off-topic / kinda not:
I think YouTube in general isn't the place for filmmakers. What do you hope to get out of it? Unless you start making weekly half-rate content that aims for making some cheap laughs, you're not going to get what you want from that market.
If you want to be a filmmaker then cater to the film market. Make a short, submit to festivals, prove yourself. Find a producer who believes in you and your feature script, one that actually has connections as well (DO NOT TAKE A PRODUCER FRESH OUT OF SOME SCHOOL), and go from there.
Hell, if you're realistic, you'll stop making shorts as a primary focus. You'll move to Atlanta and get some quick jobs, join the local union, work until your back breaks, and hopefully end up almost touching the Above-the-Line positions. If you can break through that line and into the AtL jobs, you've done it. Congrats, you actually have the connections and resources (cause fuck you're making good money) to cut yourself from the studio system and try the "actual" indie route.
I've gotten flak for trashing on the indie scene before, so I'll break that usage down real quick. Indies are what this site consists of (myself somewhat included... except I work with industry equipment and fully crewed teams), we make shorts, we hope someone watches them, we're happy.
Actual indies are making films in the 100 thousand + range up to 2 million (I think? Might be 3 million). They are selling their overseas rights, they are making profit, they pay a full crew, they have connections and resources to make full-scale connections. THAT is the indie you should want to be apart of. NOT YouTube Indie.