Specifying maximum key frame interval and new resolution in ffmpeg?

[pxstein]

From (other) encoding GUIs I know that I can specify (for AVC/H.264 encoding) a maximum key frame interval (e.g. max 200).
How do I do this at the ffmpeg command line?

Furthermore I would like to resize the output video to lets say 640*400 pixel.
How do I specify this new resolution at the cmdline for ffmpeg?

[poisondeathray]

a maximum key frame interval (e.g. max 200).
How do I do this at the ffmpeg command line?

-g 200

Furthermore I would like to resize the output video to lets say 640*400 pixel.
How do I specify this new resolution at the cmdline for ffmpeg?

-s 640x400

[pxstein]

Ok, thank you.

Do I have to enter these option in a two-pass encoding (for H.264) in BOTH steps or only the last (second pass) command?

[Selur]

both paths

[pxstein]

Thank you but sorry I have still a special question:

Assume I have a source video with an unknown resolution and unknown aspect ratio.
Now I want to shrink the video to a width of 800. The height should be automatically adjusted so that the aspect ratio of the source is kept.
How can I specify that?

Would

-s 800x

work (mind the missing height value)?

[poisondeathray]

It gets tricky with different PAR (pixel aspect ratio) values (also called SAR, or sample aspect ratio), you need some equations with padding (for letterbox/pillarbox) , I'm not sure how to do it exactly in ffmpeg . Selur probably knows , he probably has something implemented in his hybrid GUI program

But for simple square pixel example , use "-1" to calculate dimension from source

e.g.
-vf scale=w=800:h=-1


EDIT: maybe this will help for the different AR examples, but it needs to be modified
http://ffmpeg.org/pipermail/ffmpeg-user/2011-July/001746.html