I've now downloaded about 200 trailers. In each case, my objective was to find the best quality original (i.e., valid, not some fan-made crap) trailer available. Also, I wanted a trailer for
every movie on my wish list, that I have media for, and that I have viewed in the recent past. So the age and type of movie varied greatly, as did the quality of trailers I ultimately found.
The main thing I learned was that there are really two separate issues involved in this question. First, whether or not a trailer exists and the quality of those that do depend on the age and popularity of the movie. Any recent release of a popular movie will have HD trailers, and they will be very easy to find. Tricks may needed to download them, but that's another matter. Movies more than just a few years old are not as likely to have HD trailers. Some searching will be required to find them among more common lower resolution trailers that were the standard at the time of release. As the movie gets older, it becomes less likely a HD (or anything that can be viewed full screen) is available. Very popular movies, of course, are re-released with a new trailer. Or, more likely, re-issued on DVD with a remastered trailer which is made available by the publisher or otherwise finds it's way onto the Internet. I originally assumed there would be more good quality trailers for old movies—provided by people who have ripped them from DVD's—but that doesn't seem to be the case.
So the second issue is the determination of the best method for searching for a trailer—given the nature of the movie (i.e., the first issue). If it's a current release, it makes sense to avoid the crap on Youtube and go straight to where there are
only HQ original trailers posted. I found
HD-Trailers.net a good choice for that (once I decided downloading a 100+ MB file for a 2 minute trailer wasn't totally insane). The same trailers are readily available elsewhere, in different formats and resolutions. For older movies, Youtube often seemed the best source. It's frustrating searching through the crap, but using
Greasemonkey scripts to identify and highlight the HD versions makes it a lot easier. In some cases, I found doing a Google search that excluded Youtube helpful. Interestingly, the Youtube results are still included (obviously because it's owned by Google), but shown separately
after any other results. That search often confirmed there was no other good source available, so I could then be more focused on finding the best available on Youtube.
Looking at it this way, it's difficult to imagine how the search process could be automated. I don't see any effective substitute for the necessary user judgments in determining the best source to check first, which trailer to choose based on attributes and descriptions available, when it's necessary to play the trailer to determine quality or validity, etc. Also, I wonder if it's feasible or practical to duplicate the various "tricks" used to download via Firefox (i.e., modifying pages using Greasemonkey, and downloading using
DownloadHelper).