[FFmpeg-user] Detect if an MTS file is interlaced or not?

[Thomas Worth]

I'd like to know if there's a way to tell if an MTS file is
interlaced, preferably without having to decode it first. The problem
I have is that libav always returns 59.94 for the frame rate of
interlaced NTSC streams, even though we know it's 29.97. And of
course, r_frame_rate always returns 0 with the "mpegts" format so I am
left to calculate the frame count manually. I need the correct frame
rate to do this, however and there's no way of telling ahead of time
whether the input video will be interlaced or not. Any ideas?