Seeking in any large MKV H.264 video works very slow.
Call of av_seek_frame() in my code using FFmpeg LibAV takes about 3-10 seconds to jump to a middle position in 1-2 hours video.
I tried all combinations of flags: AVSEEK_FLAG_BACKWARD, AVSEEK_FLAG_BYTE, AVSEEK_FLAG_ANY, AVSEEK_FLAG_FRAME
However VLC seeks very fast in same MVK videos.
Seeking in MP4 H.264 works instantly. The problem is only with MKV.
Latest FFmpeg 4.1.3.