One of the most commonly asked questions on Freenode/#ffmpeg is how to use it to encode videos for YouTube in accordance to Googles Recommended upload encoding settings. Conforming to the guideline is rather simple, but not straightforward for the newcomer.
1. Get newish ffmpeg
Get decently new and updated ffmpeg - the current stable release is 2.7.
brew install ffmpeg
Get a 64-bit static build from Zeranoe's site.
Get a 64-bit static build from Linux static build site.
2. The command line
ffmpeg -i <input file> -codec:v libx264 -crf 21 -bf 2 -flags +cgop -pix_fmt yuv420p -codec:a aac -strict -2 -b:a 384k -r:a 48000 -movflags faststart <output_name>.mp4
This should suffice for full conformity. Explanation of parameters used:
|-codec:v libx264||set video codec to H.264|
|-crf 21||set video quality. Lower number means higher quality. 21 is a reasonable default which will create videos with bitrates as per guideline.|
|-bf 2||maximum 2 B-frames as per guideline|
|-flags +cgop||closed GOP as per guideline|
|-pix_fmt yuv420p||chroma subsampling 4:2:0 as per guideline|
|-codec:a aac -strict -2||set audio codec to AAC|
|-b:a 384||set audio bitrate to 348k, set this to 512k if you have 5.1 audio|
|-r:a 48000||set audio samplerate to 48000Hz as per guideline|
|-movflags faststart||put MOOV atom at the front of the file|
If any of the parameters don't work properly, check your ffmpeg version. Especially Ubuntu 12.04/14.04 and other Debian based distros package obsolete ffmpeg as part of their apt repositories.