Repeated replay with set rate half speed

[sanmool]

Hi,

After setting libvlc_media_player_set_rate(0.5), I repeated playing a region of 3 seconds in my video(for example between 00:02:00 and 00:02:03).
For avi file it works smoothly well, but for mp4 file, many times, it plays only last 1 second or less with some hiccups. I don't know if it is a bug or a limit of mp4 file itself.
Is there any way to repeated replay smoothly with set_rate?

I thought I could make it work smoothly by playing audio track only. I tried "--no-video" option, but it is the same. This may process video track on background and it is just not visible. Is there any way to process only audio tracks so that I might solve this problem?