Same problem, this worked for me also -- and by the way -- it's not another program to use instead of Mpeg streamclip, it just includes codecs so that now mpeg streamclip will work (I wasn't sure when I first read this)
None of my videos could be opened with iMovie. I was told to convert them with MPEG Streamclip. MPEG Streamclip would play my videos but not the audio so when i tried to use it to convert for iMovie it produced a file that would open in iMovie but without any audio. I tired a lot of the above recommendations. but this following two step process was the only thing that worked with my videos:
1 - use Handbrake (a free download) to convert video to .mp4 file When .mp4 file was then opened in MPEG Streamclip the audio played.
2 - Use MPEG Streamclip 1.9.2 to Export .mp4 file to .mov file
Then you can Import the .mov file to iMovie and you will have video and audio.
I had the same problem. All my AVI conversions had No Sound.
I had the latest version of MPEG Streamclip (1.9.3b1) - "Didn't work"
I had the latest version of Perian - "Still didn't work"
The links above to version 1.9.1, and on a Google Search, don't provide the old application
Then, after downloading 1.9.2 I tried again - "Still didn't work"
...but then I noticed that when I Converted to Quicktime (creates .mov file), the sound setting always said "Uncompressed"
I simply went back to Convert to AVI, and selected the Sound setting, changing it to "Uncompressed"...
When you go to File open files (in version 1.9.3 beta at least) there is a drop down menu at the bottom of the pop up that says video files. Click that and select all files. Then select your file. It then opens with both video and audio in mpeg stream clips! Then you can export it to whatever you want with both audio and video.