2007-8-6 Update: Based on the my own FLV conversion knowledge, I have started a Web 2.0 service call – VCASMO. It is a video + PowerPoint online presentation platform.

Convert other video to FLV
ffmpeg -i video.avi -ar 22050 -ab 32 -f flv -s 320x240 video.flv
-i input file name
-ar audio sampling rate in Hz
-ab audio bit rate in kbit/s
-f output format
-s output dimension

Convert other video to FLV with metadata
You have to install flvtool2, too, see my previous post
ffmpeg -i video.avi -ar 22050 -ab 32 -f flv -s 320x240 - | flvtool2 -U stdin video.flv

Convert FLV to jpg sequence
ffmpeg -i video.flv -an -r 1 -y -s 320x240 video%d.jpg
-i Input file name
-an disable audio
-r fps
-y overwrite file
-s output dimension

Convert particular frame to jpg
ffmpeg -i video.flv -an -ss 00:00:03 -t 00:00:01 -r 1 -y -s 320x240 video%d.jpg
-ss record start time
-t record end time last for
So if you want to save frame 4 (00:00:04) -ss 00:00:03 -t 00:00:01. Note: it is count from 00:00:00. Even you want to save one jpg, you still need to use %d for naming, it is strange that I grab one frame for one second, it will return two identical jpg files for me

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