Scaling videos of variable size to a fixed aspect ratio

Question

I have 45 videos of varying aspect ratios and resolutions. I need to scale all of them so that they fit neatly inside a 640x360 (16x9) container with the following specs:

16x9, 640x360, 1600kbps, H.264, MP4, progressive, 29.97

For example, some videos might be 512x12, others might be 480x320, but they all have to fit, scaled and centred, inside a new 640x360 output video. If a video is not wide enough to fill that space, black bars should be added on the left and right.

Is this possible with ffmpeg?

Here's the code I've been toying with so far:

ffmpeg -i "input.mov" -b:v 1600k -bufsize 1600k -r 29.97 -vf scale=640:360 -vcodec libx264 output.mp4

This seems to do everything I need, except for dynamically scaling to that fixed resolution.

Does anyone know how to achieve the result I'm looking for?

Thanks!

Answer 1

Use

ffmpeg -i "input.mov" -vf 
          "scale='if(gt(a*sar,16/9),640,360*iw*sar/ih)':'if(gt(a*sar,16/9),640*ih/iw/sar,360)',
          pad=640:360:(ow-iw)/2:(oh-ih)/2,setsar=1"
       -vcodec libx264 -b:v 1600k -bufsize:v 1600k -r 30000/1001 output.mp4

The scale filters use the conditional if(a,b,c) expression i.e. if a then b else c. I check if the video is wider than 16:9. If yes, I scale the width to 640 and scale height to preserve proportion. If not, I scale height to 360, and keep width proportional. Then the result is padded out to 640x360. The setsar is used to make sure ffmpeg registers the video as square-pixel.