Cannot find video plugin: video/x-gst-fourcc-AVin-Decoder
Decoding of AVin (AVC-Intra format from Avid) is not supported by gstreamer & not very well or at all by libav. (libavcodec, etc.)
It is supported by recent versions of the real ffmpeg and possibly some apps built off of it.
A sample file that is probably similar to yours is here:
http://samples.ffmpeg.org/ffmpeg-bugs/trac/ticket524/AVCI50.mov
I can play it fine in a recent mpv that uses ffmpeg, nothing else can handle. So you may need to re-encode it to something Pitivi can deal with.