Sorry, I don't even know what codecs there are, let alone which ones work with iMovie.
Too many codecs.
iMovie should just work for what you are doing. You should not have to know what codecs are, get third-party software, get all nerdy about this sort of project.
I understand that completely, and my editing background probably helps me a lot with all the codecs out there, but since there are so many codecs out there, one can't expect one application to be able to read all available codecs, just because people want to use .avi files with iMovie.
Not even professional video editing applications support importing all formats and codecs.
And one does not get to be nerdy when it comes to codecs, one can simply learn to understand, that there are countless of codecs out there, and that many are simply not supported by every application. If one cannot spend the time to learn such things, which can be learned in less than five minutes via a search engine, then of course, frustration will be happy to assist that fella.
I've been all over the internet in anticipation of getting a camera with video and there are a lot of questions and confusion out there. You aren't the only one. Apple likely will address these issues, but you know that they sometimes go on to other things for awhile.
Apple will probably not address such issues, but if you get a camcorder, that uses AVCHD or another MPEG-4 variant, you can almost always import the footage into iMovie.
If you are looking for a P&S or DSLR or similar photo camera, that has video recording capabilities, then it gets more complicated, as the video recording features are an add-on most of the time, thus no really easy format and system to import the footage has been employed. And as modern video recording capable cameras also use an MPEG-4 codec variant, it will again be problematic to simply import those files in iMovie.
And another problem is the audio, sometimes it gets properly embedded using no compression, sometimes it gets embedded using compression, and sometimes that audio codec can also be the source of the problem, when importing to iMovie.
In other words, due to the ****ing plethora of codecs and vendors, and the ****ing incapability of these vendors to agree on one or two universal formats, the customer is being ****ed.
Anyway,
MPEG Streamclip is a very good and free tool to transcode almost any format to an iMovie compatible format, and if one still has problems using such applications, answers are just a search away.
And in order to find out, what video and audio codec a video uses, you can use the following:
PS: Currently I am importing a .mov file recorded with the Canon EOS 5D II, the video is compressed with the H.264 codec, which is a codec Apple supports. The audio is uncompressed, thus almost all video editing applications support that too.
After that import finished, I tried an .mp4/.m4v file I transcoded with
HandBrake from a video DVD using MPEG-4 (FFmpeg) as video codec and MP3 (lame) as audio codec.
iMovie wouldn't let me import that.
After that, I tried the same clip/title from the video DVD and now used AAC as audio codec (supported audio codec in iTunes). Guess what, iMovie could import that video file, and it was not due to the video codec, as it still was the MPEG-4 (FFmpeg) codec and not H.264 (an MPEG-4 codec variant).
And now I also tried it via
MPEG Streamclip and used the x.264 codec for video and Uncompressed for audio, iMovie couldn't import that either.
Too Long To Read:
There is an abundance of video and audio formats and codecs (to compress video and audio and save storage space), don't expect any application to support all of them. Learning some basics about video and audio formats and codecs can be done via searching the world wide web of information in fifteen minutes. If that time is too much for someone, who wants to use a tool (iMovie is a tool) and use it properly, why bother learning anything?
Example:
Which file types does iMovie 09 accept?
