Width - (w)
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.
https://ik.imagekit.io/demo/sample-video.mp4
https://ik.imagekit.io/demo/sample-video.mp4?tr=w-300
Notice that the height is automatically adjusted to maintain the aspect ratio.
To reduce the width to half, use the following URL. https://ik.imagekit.io/demo/sample-video.mp4?tr=w-iw_div_2
Height - (h)
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.
https://ik.imagekit.io/demo/sample-video.mp4
https://ik.imagekit.io/demo/sample-video.mp4?tr=h-300
Notice that the width is automatically adjusted to maintain the aspect ratio.
To reduce the height to 40 percent of original, use the following URL. https://ik.imagekit.io/demo/sample-video.mp4?tr=h-ih_mul_0.4
Aspect ratio - (ar)
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 you specify both height(h) and width(w) in the URL along with aspect ratio(ar), then the aspect ratio is ignored.
URL - https://ik.imagekit.io/demo/sample-video.mp4
URL - https://ik.imagekit.io/demo/sample-video.mp4?tr=ar-4_1,h-100
To double the aspect ratio with width 400px, use the following URL. https://ik.imagekit.io/demo/sample-video.mp4?tr=w-400,ar-iar_mul_2
Crop, Crop Modes, and Focus
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.
Tip for choosing the right cropping strategy
When choosing among different strategies for cropping, think in terms of your website layout and desired output video dimension.
- 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.
Pad resize crop strategy - (cm-pad_resize)
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.
Example - All padding on one side
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.
https://ik.imagekit.io/demo/sample-video.mp4?tr=w-400,h-200
The video is 400x200 but it is cropped from all sides to preserve the aspect ratio.
https://ik.imagekit.io/demo/sample-video.mp4?tr=w-400,h-200,cm-pad_resize,bg-F3F3F3
The video is exactly 400x200 and there is no cropping. Extra padding with background color F3F3F3 has been added to get 400x200 output dimensions.
https://ik.imagekit.io/demo/sample2.mp4?tr=w-400,h-200,cm-pad_resize,bg-blurred
The video is exactly 400x200 and there is no cropping. The extra padding added consists of a blurred background made using the source video to get 400x200 output dimensions.
You can also control the focus point using fo parameter to move the actual content to one side using relative positioning.
We added the fo-left
. Now, all the padding is on the right of the video.
Forced crop strategy - (c-force)
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.
Max-size cropping strategy - (c-at_max)
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.
Min-size cropping strategy - (c-at_least)
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.
Maintain ratio crop strategy - (c-maintain_ratio)
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.
By default, ImageKit.io crops the video from the center, but you can change this using the focus parameter.
URL - https://ik.imagekit.io/demo/sample-video.mp4
URL - https://ik.imagekit.io/demo/sample-video.mp4?tr=w-400,h-300,c-maintain_ratio
w-400,h-300,c-maintain_ratio
is equivalent to w-400,h-300
because maintain_ratio
is the default crop strategy.
Notice that the video's dimension matches 400x300, but the content is cropped from all edges, i.e., by default, ImageKit will extract the video from the center.
URL - https://ik.imagekit.io/demo/sample-video.mp4?tr=w-400,h-300,c-maintain_ratio,fo-left
Using the focus (fo
) parameter, you can specify the side to crop from.
Here the video's dimension matches 400x300 and crops out the content on right side, because focus (fo
) is set to left
.
Extract crop strategy - (cm-extract)
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.
By default, ImageKit.io extracts the video from the center but you can change this using the focus parameter.
Examples - Center and relative focus
URL - https://ik.imagekit.io/demo/sample-video.mp4?tr=h-300,w-300,cm-extract
A 300x300 part is extracted from the center of the original video.
In the relative method, you can use the focus (fo) parameter to specify that the extract should be done from, let's say, the bottom of the original video.
URL - https://ik.imagekit.io/demo/sample-video.mp4?tr=h-300,w-300,cm-extract,fo-bottom
Focus - (fo)
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:
left
,right
,top
,bottom
can be to control the position of padding when used with pad resize. Learn from examples.center
,top
,left
,bottom
,right
,top_left
,top_right
,bottom_left
andbottom_right
can be used to define relative cropping during extract crop. Learn from examples.
Beyond static positioning, the fo
parameter also supports AI-powered smart cropping that can automatically detect and track subjects throughout your video. This includes automatic smart crop (fo-auto
) for general content, face detection and tracking (fo-face
), and object-aware cropping (fo-<object>
) that can focus on specific objects like people, cars, or animals from our supported object list.
Automatic smart crop - (fo-auto)
Automatically detects and tracks the most important objects in your video, ensuring they remain centered as the video progresses. This feature is ideal for creating engaging social media content from longer videos. When using fo-auto
, you must specify both dimensions—either provide both height
and width
, or specify one dimension along with the ar
(aspect ratio) parameter. The unspecified dimension will be calculated automatically to maintain the aspect ratio.
URL - https://ik.imagekit.io/demo/skateboarding.mp4?tr=fo-auto,w-300,ar-3_4
The AI automatically keeps the skateboarder in focus while converting to a vertical format, perfect for social media.
URL - https://ik.imagekit.io/demo/skateboarding.mp4?tr=fo-auto,w-480,h-360,cm-extract
Extract a precise 480×360 section while keeping the action centered throughout the video.
Face crop - (fo-face)
Detects and follows faces in your video, automatically keeping them centered and in focus. When multiple faces are present, it focuses on the most prominent one.
URL - https://ik.imagekit.io/demo/speak-phone.mp4?tr=fo-face
Automatically determines the optimal crop size to keep the face in focus throughout the video.
URL - https://ik.imagekit.io/demo/speak-phone.mp4?tr=fo-face,ar-9_16
Perfect for creating vertical videos for mobile platforms while keeping the face centered.
URL - https://ik.imagekit.io/demo/speak-phone.mp4?tr=fo-face,w-400,h-600,cm-extract
Extract a 400×600 portion while keeping the face optimally positioned.
Object-aware cropping - (fo-object name)
Focus on specific objects in your video by specifying any object from the supported list. The AI will track and keep the specified object in focus throughout the video.
URL - https://ik.imagekit.io/demo/bench.mp4?tr=fo-dog
Intelligently crop the video to keep the dog in the view.
URL - https://ik.imagekit.io/demo/bench.mp4?tr=fo-person
Intelligently crop the video to keep the person in the view.
Auto-sizing with smart crop: When using face crop (fo-face
) or object-aware cropping (fo-<object>
), you can omit width and height parameters to let the AI automatically determine the optimal crop size. Use the ar
parameter to specify your preferred aspect ratio, and the AI will adjust the crop area to match while keeping the subject in focus.
Limitations and considerations for video smart crop
Crop mode compatibility: Video smart crop only works with c-maintain_ratio
(default) and cm-extract
crop modes. All other crop modes (defined with c
or cm
) are invalid.
- Video smart crop is available when base asset is video and inside video overlays (
l-video
). However, video smart crop is not available when input video codec isMPEG-1 Video
orMPEG-2 Video
. - Video smart crop is not available when input of video layer (
l-video
) is a GIF file. - Video smart crop is not available for image overlays (
l-image
) in video transformations. - Smart crop can only be performed on a video once, and it must be the first step of the chained transformations.
tr=b-10_red:fo-person
- ❌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. - You cannot use rotate (
rt
) in the same step as smart crop.tr=fo-person,rt-90
- ❌
If you want to rotate a video after applying smart crop, use chained transformation (separate the parameters with a:
).tr=fo-person:rt-90
- ✅ will first crop around theperson
in the video, and then rotate the result by 90 degrees. - Arithmetic expressions are completely unsupported anywhere in the transformation when video smart crop is used.
Video smart crop pricing
Video smart crop incurs additional charges beyond the standard video encoding costs. The smart crop fee is calculated based on two factors:
- Duration of the final video output (in seconds).
- Number of smart crop operations used in the transformation.
The formula for calculating the smart crop cost is:
Smart crop cost = Final video duration (in seconds) × Number of `fo` parameters used × VPU rate for SD video