Re-sampling H264 video to reduce frame rate while maintaining high image quality

A lot has changed since this posting in 2012. I am adding this answer for people like me who find this from the search engines. I had good luck with the following:

ffmpeg -y -i source.mp4 -r 25 -s 160x90 -c:v libx264 -b:v 3M -strict -2 -movflags faststart destination.mp4

Here’s a short explanation on what every parameter does:

• -y : overwrite output files without asking
• -i source.mp4 : input file name
• -r 25 : output frame rate (in frames per second)
• -s 160x90 : output frame size (in pixel) – inserts the scale video filter
• -c:v libx264 : output video encoder
  • -c:v is short for -codec:v and -vcodec
• -b:v 3M : video bitrate (in bit/s) passed to libx264 encoder
• -strict -2 : governs standards compliance; -2 allows experimental features – required to enable native FFmpeg AAC audio encoder in builds older than version 2015-12-05, see here, AAC is now the default audio encoder.
• -movflags faststart : move the index to the beginning of the output file (mov and mp4 format specific parameter)

For more details see the official documentation.