I'm trying to split video by subtitles and encode into .mp4(h.264/aac) using ffmpeg, but it takes so much time! First pieces of video are splited and encoded really fast, but for each iteration time increases, and so 40 min video takes all night or more. Small 3 min video takes max 10 mins.

cmd for splitting and encoding:

ffmpeg -i filename.avi -ss 00:00:0(time of sub start) -t 0:0:3(time of sub duration) -acodec libfaac -vcodec libx264 -bf 0 -f mp4 filename.mp4

ffmpeg version N-34849-g07c7ffc (last, i think)

How I can make it faster? Are there, maybe, some magic arguments for ffmpeg or some hacks?