This eliminates the need for finding the dimensions of the input video prior to encoding. So I'm using a FFMPEG PHP Library which is actually in a Laravel wrapper (and if you don't know what that means don't worry because this is more of a map question.

trunc(*iw/2)*2 and trunc(*iw/2)*2 ensure that the dimensions are divisible by 2 by dividing by 2, making the result an integer, then multiplying it back by 2.

min(1,min(720/iw,400/ih) finds the scaling factor to fit within the bounding box (from here), constraining it to a maximum of 1 to ensure it only downscales, and.

Using Variables There are also some useful variables which can be used instead of numbers, to specify width and height of the output image. In this case, you can use expression evaluation in the scale function, like that used in Charlie's answer.Īssuming an output bounding box of 720x400: ffmpeg -i input.jpg -vf scale320:-2 output320.png The output will now be 320×206 pixels.

However, this does not work if your input video has a weird size and you are encoding to a format that requires the dimensions to be divisible by 2, resulting in an error. If you are trying to fit a bounding box, then using force_original_aspect_ratio as per xmedeko's answer is a good starting point. When I said 'if frigate scales the image itself', I suppose I was thinking of the ffmpeg subprocess as basically part of frigate from the users perspective.

Ffmpeg scale and stretch