Thank you for answer, Paul.
Movie is ProRES MOV movie, it's has no key frames. ProRES uses intra-frame compression(not inter-frame), and it does not need key frames.
I've googled seekToTime and found that AVPlayer uses CMTime with timeScale parameter, which is how many fractions are in 1 sec. In cinder seekToTime() works like it has timeScale set to 1. But in cinder SeekToTime() has no parameter timeScale.
In QuickTimeImplAvf.mm there is a code:
CMTime seek_time = CMTimeMakeWithSeconds(seconds, [mPlayer currentTime].timescale);
[mPlayer seekToTime:seek_time toleranceBefore:kCMTimeZero toleranceAfter:kCMTimeZero];
timescale is taken from mPlayer, which is of AVPlayer* type. But there is no access to AVPlayer class in cinder (MovieBase has getPlayerHandle(), but it's not possible to access members of returned object).
Is there a way to access it? Or, may be problem is somewhere outside of AVPlayer?