Overlays in video

Overlay
In ImageKit, you can add images, text, subtitles, and videos over a base video using layers. Skip to the relevant section to understand with a quick example:
​Add images over video​
​Add text over video​
​Add video over video​
​Add subtitles over video​
Layers
A layer is a special kind of transformation that allows you to modify the overlay itself and express its position in relation to the parent.
Syntax of layers
A layer starts with l-<type> and ends with l-end. All the positional and transformation parameters of that layer are between l-<type> and l-end and only apply to that layer and not the parent base asset.
type can be image, text, video or subtitles.
For example, in the following URL, we are adding a logo image logo.png on top of a base video, i.e. sample-video.mp4. However, we applied width (w-10) and rotation (rt-90) transformations on this overlay logo image before placing it on the base video. Transformations w-300,h-300 are applied to sample-video.mp4.
Here the parent base video has one layer inside it. A layer can also nest another layer.
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        URL-endpoint           Base video                                   Layer
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┌──────────────────────────┐┌──────────────┐                ┌─────────────────────────────────┐
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https://ik.imagekit.io/demo/sample-video.mp4?tr=w-300,h-300,l-image,i-logo.png,w-10,rt-90,l-end
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                                                └────┬────┘                    └────┬────┘
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                                                     │                              │
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                                                     │        These transformations are applied to logo.png
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                                                     │
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                           These transformations are applied to sample-video.mp4
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Input of layer
The input of the layer can be specified using i or ie (base64 encoded) parameter. In case both i and ie is present, i is ignored. The base64 string should be made URL safe to ensure that all padding characters(=) are included correctly. In Javascript, a function like encodeURIComponent() can be used for this.
Position of layer
The position of the layer can be controlled using the following parameters. The position of the layer is always relative to the immediate parent. For instance, the parent is the base video in the above example, and the logo image is the nested layer.
The position of subtitles cannot be controlled at this point.
Parameter
Description
lx
x of the top-left corner in the base asset where layer's top-left corner would be placed.
ly
y of the top-left corner in the base asset where layer's top-left corner would be placed.
lfo
Position of layer in relative terms e.g. center, top, left, bottom, right, top_left, top_right, bottom_left and bottom_right. Default value is center.
lso
Start time of the base video in seconds when the layer should appear.
ldu
Duration in seconds during which layer should appear on the base video.
leo
End time of the base video when this layer should disappear. In case both leo and ldu are present, ldu is ignored.
Transformation of layer
You can apply transformations to the layer as you would otherwise. However, any transformation parameter inside the layer is only applicable to that layer and not the parent.
However, different types of layers support different types of transformations which are covered in respective sections.
​Transformation of images overlay​
​Transformation of text overlay​
​Transformation of video overlay​
​Transformation of subtitles overlay​
Transformations inside a layer can be chained together to achieve the desired outcome.
Nesting of layers
A layer can have a nested layer up to 3 levels.
For example, in the below URL, i-inner.png is rendered on the top-left corner of i-outer.png using the lfo-top_left parameter.
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                          Parent layer
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┌──────────────────────────────────────────────────────────────┐
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l-image,i-outer.png,l-image,i-inner.png,lfo-top_left,l-end,l-end
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                    └──────────────────┬──────────────────┘
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                                       │
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                                  Nested layer
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Add images over video
You can add an image over a base video using the following example.
Usage syntax
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https://ik.imagekit.io/demo/base-video.mp4?tr=l-image,i-logo.png,l-end
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You can also control the position of image overlay using these positional parameters.
Transformation of image overlay
ImageKit supports many image transformation parameters, however inside a layer, you can apply the following transformations to the image overlay before it is placed on the base video. You can chain the transformations one after other to achieve the desired outcome.
Parameter
Description
​w​
Width of overlay image.
​h​
Height of overlay image.
​ar​
Apect ratio of overlay image.
​c​
Cropping method. Accepts force, at_max, and at_least.
​cm​
Crom mode. Supports extract and pad_resize.
​fo​
Relative focus area used during cropping. Accpets center, top, left, bottom, right, top_left, top_right, bottom_left and bottom_right.
​b​
This adds a border to the overlay image. It accepts two parameters - the width of the border and the color of the border in format b-<border-width>-<hex code>
​bg​
It is used to specify the background color in RGB Hex Code (e.g. FF0000) or an RGBA Code (e.g. FFAABB50) that must be used for the image. If you specify an 8 character background, the last two characters must be a number between 00 and 99 , which is used to indicate the opacity level of the background. 00 represents an opacity level of 0.00, 01 represents opacity level 0.01, and so on.
​r​
It is used to control the radius of the corner. To get a circle or oval shape, set the value to max.
Add text over video
You can add any text string over a base video using the following example.
Usage syntax
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https://ik.imagekit.io/demo/base-video.mp4?tr=l-text,i-hello,l-end
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You can also control the position of text overlay using these positional parameters.
Transformation of text overlay
Following transformation parameters are supported on the text inside a layer.
Parameter
Description
w
Width of the whole text layer.
h
Height of the whole text layer.
fs
Font size
ff
Font family
co
Color
ia
Inner alignment. Accepts left, right and center. The default value is center.
pa
Padding
al
Alpha
tg
Typography
​bg​
It is used to specify the background color in RGB Hex Code (e.g. FF0000) or an RGBA Code (e.g. FFAABB50) that must be used for the video. If you specify an 8 character background, the last two characters must be a number between 00 and 99 , which is used to indicate the opacity level of the background. 00 represents an opacity level of 0.00, 01 represents opacity level 0.01, and so on.
​r​
It is used to control the radius of the corner. To get a circle or oval shape, set the value to max.
Add video over video
You can add video over a base video using the following example.
Usage syntax
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https://ik.imagekit.io/demo/base-video.mp4?tr=l-video,i-overlay.mp4,l-end
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You can also control the position of video overlay using these positional parameters.
Transformation of video overlay
You can transform the layer video using any supported video transformation parameter in ImageKit except sr.
Add subtitles over a video
You can add subtitles over a base video using the following example.
Usage syntax
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https://ik.imagekit.io/demo/base-video.mp4?tr=l-subtitles,i-english.srt,l-end
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The position of subtitles cannot be controlled in the beta version.
Transformation of subtitles overlay
Transformation of subtitles are not supported in the beta version.