VideoFrameCapturer for pushing frames directly (#538)

* VideoFrameCapturer for pushing frames directly

* changeset and spotless

+---
+"client-sdk-android": patch
+---
+
+Added VideoFrameCapturer for pushing video frames directly

+/*
+ * Copyright 2024 LiveKit, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.livekit.android.room.track.video
+
+import android.content.Context
+import livekit.org.webrtc.CapturerObserver
+import livekit.org.webrtc.SurfaceTextureHelper
+import livekit.org.webrtc.VideoCapturer
+import livekit.org.webrtc.VideoFrame
+
+/**
+ * A [VideoCapturer] that can be manually driven by passing in [VideoFrame] to [pushVideoFrame].
+ *
+ * Once [startCapture] is called, call [pushVideoFrame] to publish video frames.
+ */
+open class VideoFrameCapturer : VideoCapturer {
+
+    var capturerObserver: CapturerObserver? = null
+
+    // This is automatically called when creating the LocalVideoTrack with the capturer.
+    override fun initialize(helper: SurfaceTextureHelper, context: Context?, capturerObserver: CapturerObserver) {
+        this.capturerObserver = capturerObserver
+    }
+
+    override fun startCapture(width: Int, height: Int, framerate: Int) {
+        capturerObserver?.onCapturerStarted(true)
+    }
+
+    override fun stopCapture() {
+        capturerObserver?.onCapturerStopped()
+    }
+
+    override fun changeCaptureFormat(width: Int, height: Int, framerate: Int) {
+    }
+
+    override fun dispose() {
+    }
+
+    override fun isScreencast(): Boolean = false
+
+    fun pushVideoFrame(frame: VideoFrame) {
+        capturerObserver?.onFrameCaptured(frame)
+    }
+}