libx264 for FCP 7
 

I've been given some video files to edit that Quick Time inspector identifies as libx264.
(29.97, data rate:15.46 Mbit/s)

I regularly transcode H.264 files to ProRes 422 with mpeg streamclip and edit with FCP 7 on an iMac (10.9.5)

When I try that with these files they get "glitchy", artifacting for a frame every few seconds.
What else can I use to get them into FCP7?

Some play fine before the transcode, some are glitchy in the original format, which makes me suspect a card that wasn't class 10, but that wouldn't seem to explain the files that play well before transcode.

Thanks
Tom