[VIDCS-922] Add Video transformers sample (#289)

* Add Video transformers sample

* Add Video Transformers smaple to travis build

* Add a complete README with examples

* Include the installation steps

* Remove commented code showing how to remove transformers from publisher stream

* Add Changelog file with know issues

* Button to toggle Video transformers

---------

Co-authored-by: pvenum <[email protected]>

Video-Transformers/CHANGELOG.md

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+# Video Transformers Changelog
+
+All notable changes to this project will be documented in this file.
+
+## 2.25.2
+
+### Added
+
+- Support pre-built transformers in the Vonage Media Processor library or create your own custom video transformer to apply to published video.
+
+### Known issues
+
+- When using Vonage's Background Blur, the ML model is not being automatically added to the main bundle. It is required to be added manually: 
+  - Select the target for which you want to add the file. Go to the "Build Phases" tab.
+  - Expand the "Copy Bundle Resources" section.
+  - Click the "+" button to add a new file. A file picker dialog will appear. Choose ./Pods/VonageClientSDKVideo/OpenTok.xcframework/ios-arm64/OpenTok.framework/selfie_segmentation.tflite
+
+### Fixed
+
+- NA
+
+### Enhancements
+
+- NA
+
+### Changed
+
+- NA
+
+### Deprecated
+
+- NA

Video-Transformers/Podfile

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+require_relative '../OpenTokSDKVersion'
+
+platform :ios, '13'
+use_frameworks!
+
+target 'Video-Transformers' do
+  pod 'VonageClientSDKVideo', '2.25.2'
+end

Video-Transformers/README.md

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+Video Transformers
+======================
+
+The Video Transformers app is a very simple application created on top of Basic Video Chat meant to get a new developer
+started using Media Processor APIs on OpenTok iOS SDK. For a full description, see the [Video Transformers tutorial at the
+OpenTok developer center](https://tokbox.com/developer/guides/vonage-media-processor/ios).
+
+You can use pre-built transformers in the Vonage Media Processor library or create your own custom video transformer to apply to published video.
+
+You can use the OTPublisherKit.videoTransformers properties to apply video transformers to a stream.
+
+For video, you can apply the background blur video transformer included in the Vonage Media Library.
+You can use the <a href="/developer/sdks/ios/reference/Classes/OTPublisherKit.html#//api/name/audioTransformers"><code>OTPublisherKit.audioTransformers</code></a> and
+<a href="/developer/sdks/ios/reference/Classes/OTPublisherKit.html#//api/name/videoTransformers"><code>OTPublisherKit.videoTransformers</code></a>
+properties to apply audio and video transformers to a stream.
+
+<p class="important">
+  <b>Important:</b> The audio and video transformer API is a beta feature.
+</p>
+
+For video, you can apply the background blur video transformer included in the Vonage Media Library.
+
+You can also create your own custom audio and video transformers.
+
+## Applying a video transformer from the Vonage Media Library
+
+Use the <a href="/developer/sdks/ios/reference/Classes/OTVideoTransformer.html#//api/name/initWithName:properties:"><code>[OTVideoTransformer initWithName:properties:]</code></a>
+method to create a video transformer that uses a named transformer from the Vonage Media Library.
+
+Currently, only one transformer is supported: background blur. Set the `name` parameter to `"BackgroundBlur"`.
+Set the `properties` parameter to a JSON string defining properties for the transformer.
+For the background blur transformer, this JSON includes one property -- `radius` -- which can be set
+to `"High"`, `"Low"`, or `"None"`.
+
+```objectivec
+NSMutableArray * myVideoTransformers = [[NSMutableArray alloc] init];
+OTVideoTransformer *backgroundBlur = [[OTVideoTransformer alloc] initWithName:@"BackgroundBlur"
+                                                                   properties:@"{\"radius\":\"High\"}"];
+[myVideoTransformers addObject:backgroundBlur];
+_publisher.videoTransformers = [[NSArray alloc] initWithArray:myVideoTransformers];
+```
+
+## Creating a custom video transformer
+
+Create a class that implements the <a href="/developer/sdks/ios/reference/Protocols/OTCustomVideoTransformer.html"><code>OTCustomVideoTransformer</code></a> 
+protocol. Implement the `[OTCustomVideoTransformer transform:]` method, applying a transformation to the `OTVideoFrame` object passed into the method. The `[OTCustomVideoTransformer transform:]` method is triggered for each video frame:
+
+```objectivec
+@interface CustomTransformer : NSObject <OTCustomVideoTransformer>
+@end
+@implementation CustomTransformer
+- (void)transform:(nonnull OTVideoFrame *)videoFrame {
+    // Your custom transformation
+}
+@end
+```
+
+In this sample, to display one of the infinite transformations that can be applied to video frames, a logo is being added to the bottom right corner of the video.
+
+```objectivec
+@interface CustomTransformer : NSObject <OTCustomVideoTransformer>
+@end
+@implementation CustomTransformer
+- (void)transform:(nonnull OTVideoFrame *)videoFrame {
+
+    UIImage* image = [UIImage imageNamed:@"Vonage_Logo.png"];
+
+    uint32_t videoWidth = videoFrame.format.imageWidth;
+    uint32_t videoHeight = videoFrame.format.imageHeight;
+
+    // Calculate the desired size of the image
+    CGFloat desiredWidth = videoWidth / 8;  // Adjust this value as needed
+    CGFloat desiredHeight = image.size.height * (desiredWidth / image.size.width);
+
+    // Resize the image to the desired size
+    UIImage *resizedImage = [self resizeImage:image toSize:CGSizeMake(desiredWidth, desiredHeight)];
+
+    // Get pointer to the Y plane
+    uint8_t* yPlane = [videoFrame getPlaneBinaryData:0];
+
+    // Create a CGContext from the Y plane
+    CGContextRef context = CGBitmapContextCreate(yPlane, videoWidth, videoHeight, 8, videoWidth, CGColorSpaceCreateDeviceGray(), kCGImageAlphaNone);
+
+    // Location of the image (in this case right bottom corner)
+    CGFloat x = videoWidth * 4/5;
+    CGFloat y = videoHeight * 1/5;
+
+    // Draw the resized image on top of the Y plane
+    CGRect rect = CGRectMake(x, y, desiredWidth, desiredHeight);
+    CGContextDrawImage(context, rect, resizedImage.CGImage);
+
+    CGContextRelease(context);
+}
+@end
+```
+
+Then set the `OTPublisherKit.videoTransformers` property to an array that includes the object that implements the
+OTCustomVideoTransformer interface:
+
+```objectivec
+CustomTransformer* logoTransformer;
+logoTransformer = [customTransformer alloc];
+OTVideoTransformer *myCustomTransformer = [[OTVideoTransformer alloc] initWithName:@"logo" transformer:logoTransformer];
+
+NSMutableArray * myVideoTransformers = [[NSMutableArray alloc] init];
+[myVideoTransformers addObject:myCustomTransformer];
+
+_publisher.videoTransformers = [[NSArray alloc] initWithArray:myVideoTransformers];
+```
+
+You can combine the Vonage Media library transformer (see the previous section) with custom transformers or apply
+multiple custom transformers by adding multiple PublisherKit.VideoTransformer objects to the ArrayList used
+for the `OTPublisherKit.videoTransformers` property.
+
+## Clearing video transformers for a publisher
+
+To clear video transformers for a publisher, set the `OTPublisherKit.videoTransformers` property to an empty array.
+
+```objectivec
+_publisher.videoTransformers = [[NSArray alloc] init];
+```
+
+Adding the OpenTok library
+==========================
+In this example the OpenTok iOS SDK was not included as a dependency,
+you can do it through Swift Package Manager or Cocoapods.
+
+
+Swift Package Manager
+---------------------
+To add a package dependency to your Xcode project, you should select 
+*File* > *Swift Packages* > *Add Package Dependency* and enter the repository URL:
+`https://github.com/opentok/vonage-client-sdk-video.git`.
+
+
+Cocoapods
+---------
+To use CocoaPods to add the OpenTok library and its dependencies into this sample app
+simply open Terminal, navigate to the root directory of the project and run: `pod install`.