Resize and Crop Videos

Used to specify the width of the output video. Accepts integer value greater than 1.

You can also provide an arithmetic expression such as iw_div_2, cw_mul_0.8, or ih as a value for this parameter. Doing so will first calculate the value of the expression and then apply transformations using that value. Learn more about arithmetic expressions here.

When you specify just width, the height is adjusted accordingly to maintain the aspect ratio.

Used to specify the height of the output video. Accepts integer value greater than 1.

You can also provide an arithmetic expression such as ih_div_2, ch_mul_0.5, or ih as a value for this parameter. Doing so will first calculate the value of the expression and then apply transformations using that value. Learn more about arithmetic expressions here.

When you specify only height, the width is adjusted accordingly to maintain the aspect ratio.

Used to specify the aspect ratio of the output video. It is the ratio of width to height of the output video. This parameter must be used along with either the height(h) or width(w) parameter but not both.

You can also provide an arithmetic expression such as iar_div_2, or car_mul_0.75 as a value for this parameter. Doing so will first calculate the value of the expression and then apply transformations using that value. Learn more about arithmetic expressions here.

Usage = ar-<width>-<height>

If only, one of the height(h) or width(w) is specified, then ImageKit.io adjusts the other dimension accordingly to preserve aspect ratio and no cropping takes place.

But when you specify both height(h) and width(w) dimensions, you need to choose the right cropping strategy based on your website layout and desired output video.

• If you want to preserve the whole video content without any cropping and need the exact same dimensions (height and width) in the output as requested, choose either the pad resize crop or forced crop strategy.
• If you want to preserve the whole video content without any cropping, but it is okay if one or both the dimensions (height or width) in the output are adjusted to preserve the aspect ratio. Then choose either the max-size cropping or min-size cropping strategy.
• If you need the exact same dimensions (height and width) in the output video as requested but it's okay to crop the video to preserve the aspect ratio. Then choose either the maintain ratio crop or the extract crop strategy. You can combine the extract crop strategy with different focus values to get the desired result.

In the pad resize crop strategy, the output dimension (height and width) is the same as requested, no cropping takes place, and the aspect ratio is preserved. This is accomplished by adding padding around the video to get it to match the exact dimension as requested.

In the examples above, we saw that when the video is padded using the pad resize crop strategy, the padding is equal on both sides of the video. However, there might be cases where we want all the padding to be added on only one side of the video. This can be done using the focus (fo) parameter.

In a forced crop strategy, the output video's dimension (height and width) is exactly the same as requested, no cropping takes place, but the aspect ratio is not preserved. It forcefully squeezes the original video to get it to fit completely within the output dimensions.

URL - https://ik.imagekit.io/demo/sample-video.mp4?tr=w-200,h-200,c-force

Notice that the aspect ratio is changed and the video looks squeezed.

In the max-size crop strategy, the whole video content is preserved without any cropping, and the aspect ratio is preserved, but one of the dimensions (height or width) is adjusted.

The output video is less than or equal to the dimensions specified in the URL,i.e., at least one dimension will exactly match the output dimension requested, and the other dimension will be equal to or smaller than the corresponding output dimension requested.

URL - https://ik.imagekit.io/demo/sample-video.mp4?tr=w-200,h-200,c-at_max

Notice that the aspect ratio is maintained, and there is no cropping. However, the height is reduced so that the video fits within a 200x200 container.

This strategy is similar to the max-size cropping strategy, with the only difference being that, unlike the max-size strategy, the output video dimension is equal to or larger than the requested dimensions. One of the dimensions will be exactly the same as what is requested, while the other dimension will be equal to or larger than what is requested.

URL - https://ik.imagekit.io/demo/sample-video.mp4?tr=w-200,h-200,c-at_least

Notice that the height is 200px as requested, but the width is more than 200px. The aspect ratio is maintained and there is no cropping.

This is the default crop strategy. If no crop (c) or crop_mode (cm) is specified in the URL, c-maintain_ratio gets applied automatically.

In this strategy, the output video's dimensions (height and width) are the same as requested, and the aspect ratio is preserved. This is accomplished by resizing the video to the requested dimension and then cropping extra parts to get the desired height & width.

In this strategy, the output video's dimension (height and width) is exactly the same as requested, and the aspect ratio is preserved. In this strategy, instead of trying to resize the video as we did in maintain ratio strategy, we extract out a region of the requested dimension from the original video.

This parameter can be used along with pad resize, maintain ratio or extract crop to change the behavior of padding or cropping. Learn more from the different examples shown in respective sections.

This parameter can have the following values depending upon where it is being used:

1. left, right, top, bottom can be to control the position of padding when used with pad resize. Learn from example.
2. center, top, left, bottom, right, top_left, top_right, bottom_left and bottom_right can be used to define relative cropping during extract crop. Learn from examples.

Apart from the above, the fo parameter also has additional options that intelligently focus on the most important portion or a specific object in the video. Learn more about video smart crop

In a video, the important part of the frame can shift as the timeline progresses. Using video smart crop, you can crop the video so the important parts stay in view across the timeline.

To apply smart crop, use the fo (focus) parameter to specify what we should to follow in the video. For this fo support 3 families of values:

1. Automatic smart crop (fo-auto) - Identifies all important objects in a video, and focuses at the weighted average of their spatial location.
2. Face crop (fo-face) - Focus on a face in the video. (Chooses most prominent face when multiple faces are present)
3. Object-aware crop - Mention any one COCO class objects (example: fo-person, fo-boat or fo-ball).

Video smart crop is available for video transformations and video overlays (l-video). Smart crop is not supported when input video's codec is av1, mpeg1video, or mpeg2video.

You can place GIF files in video layers if you want them as overlays, but smart crop itself is not supported for GIF inputs right now.

Smart crop can only be performed on a video once. That is only at first step of the chained transformations.

Invalid: dontopen://ik.imagekit.io/demo/birthday.mov?tr=b-10_red:fo-person

Valid: dontopen://ik.imagekit.io/demo/birthday.mov?tr=fo-person:b-10_red

If you use smart crop inside a video layer (l-video), it must also be the first step within that layer’s chained transformations.

Invalid: dontopen://ik.imagekit.io/demo/sample-video.mp4?tr=l-video,i-birthday.mov,b-10_red:fo-person,l-end

Valid: dontopen://ik.imagekit.io/demo/sample-video.mp4?tr=l-video,i-birthday.mov,fo-person:b-10_red,l-end

As best practice we recommend applying follow-up transformation, in later steps (separated by :).

Learn more about chained transformations

You cannot use rt in the same step as smart crop.

dontopen://ik.imagekit.io/demo/birthday.mov?tr=fo-person,rt-90 is invalid.

If you want to rotate (or transpose) a video after applying smart crop, use chained transformation (separated the parameters with a :).

dontopen://ik.imagekit.io/demo/birthday.mov?tr=fo-person:rt-90 will first crop around the person in the video, and then rotate the result.

Learn more about chained transformations

No. In fact arithmetic expressions are completely unsupported anywhere in the transformations, when video smart crop is used. Use explicit numeric values instead.

The cost of video smart crop is charged based on the duration of the final video output and how many smart-crop operations you request via the fo parameter.

Imagekit charges for video smart crop in VPUs (Video Processing Units). In practice we calculate the VPU based on formula below:

(Duration of the final video output in seconds) * (Number of smart-crop requested via 'fo' parameter) * (VPU cost of 1 second of SD video output)

Learn more about video transformation pricing