To find the timebase where you were originally were hard coding 90000, look here stream.time_base().den() when checked while using an mp4 file, it would return 90000. -- View this message in context: http://ffmpeg-users.933282.n4.nabble.com/timestamp-calculation-tp4653031p4671139.html Sent from the FFmpeg-users mailing list archive at Nabble.com.