Using media transforms
Sometimes there is a need to alter a media item before beginning playback. Some examples of this could be:
-
Request an authorization token to append to the stream URL
-
A server-side ad service that accepts some parameters and then returns a dynamically generated stream URL.
-
A feed is provided by a third-party service that does not match AMP’s Media interface akamai.amp.Media
A media transform can be any function that excepts a media object and returns a media object:
// synchronous transform
amp.addTransform(akamai.amp.TransformType.MEDIA, function (media) {
media.src += "&testing=1234";
return media;
});A Promise can also be returned if the transform performs any asynchronous operations: returns a media object:
// asynchronous transform
amp.addTransform(akamai.amp.TransformType.MEDIA, function (media) {
return new Promise(function (resolve, reject) {
media.src += "&hello=world";
resolve(media);
});
});A formal transform object can be provided for advanced use cases, based on the akamai.amp.Transform interface. This can be any object that contains a property called transform which is a function:
// asynchronous transform
amp.addTransform(akamai.amp.TransformType.MEDIA, {
priority: 100,
transform: function (media) {
return new Promise(function (resolve, reject) {
media.src += "&hello=world";
resolve(media);
});
}
});Using a transform object allows for a priority to be set. Transforms with higher priorities are executed first. Additionally, the transforms cascade allows transformations to occur on both the downstream and upstream:
// cascading transform
amp.addTransform(akamai.amp.TransformType.MEDIA, function (media, next) {
return new Promise(function (resolve, reject) {
var start = Date.now()
// allow other transforms to be executed before completing this function
next(media)
.then(function (result) {
result.src += "&elapsed=" + (Date.now() - start);
resolve(result);
})
});
});Calling the next() function suspends the transform and passes control to the following function in the list. When the other transforms have been completed, the function resumes.