Today, I found my MP4 files are full-downloaded, then played. If the size of the MP4 file is very large, I must wait for a long time. So, I tried to find some solution to hint MP4 files. mp4box just can do this job.
Although mp4box is a multiplexor for MP4 files, I just use it to hint my MP4 file:
# cd /usr/ports/multimedia/gpac-mp4box
# make install clean
# mp4box -hint video.mp4
Now, I can stream my MP4 files with Flash player.