Start implementation

src/index.ts

@@ -1 +1,4 @@
-console.log("hi")
+export { Output } from './output';
+export { Mp4OutputFormat } from './output_format';
+export { VideoFrameSource, CanvasSource, MediaStreamVideoTrackSource, AudioDataSource, AudioBufferSource, MediaStreamAudioTrackSource } from './source';
+export { Target, ArrayBufferTarget, StreamTarget, FileSystemWritableFileStreamTarget } from './target';