Reland of Injectable Obj-C video codecs

webrtc/sdk/objc/Framework/Classes/VideoToolbox/encoder.mm

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  *
  */
@@ skipping 519 matching lines @@
   target_bitrate_bps_ = 1000 * new_bitrate_kbit;
   bitrate_adjuster_.SetTargetBitrateBps(target_bitrate_bps_);
   SetBitrateBps(bitrate_adjuster_.GetAdjustedBitrateBps());
   return WEBRTC_VIDEO_CODEC_OK;
 }
 
 int H264VideoToolboxEncoder::Release() {
   // Need to reset so that the session is invalidated and won't use the
   // callback anymore. Do not remove callback until the session is invalidated
   // since async encoder callbacks can occur until invalidation.
-  int ret = ResetCompressionSession();
+  DestroyCompressionSession();

[jtt_webrtc, 2017/07/20 02:33:20]

This is not the problem. See
ObjCVideoEncoder::~ObjCVideoEncoder()
and
ObjCVideoDecoder::~ObjCVideoDecoder()

[kthelgason, 2017/07/20 11:33:51]

Agreed. I still think we should make this change. This is how it's done in the
decoder, and it makes little sense to recreate the compression session and then
set the callback to null.

[jtt_webrtc, 2017/07/20 17:55:59]

I'm not sure what implications this will have because Reset reinitializes the
capture session and doing this introduces uncertainty.
I rather deal with known issues for now.

   callback_ = nullptr;
-  return ret;
+  return WEBRTC_VIDEO_CODEC_OK;
 }
 
 int H264VideoToolboxEncoder::ResetCompressionSession() {
   DestroyCompressionSession();
 
   // Set source image buffer attributes. These attributes will be present on
   // buffers retrieved from the encoder's pixel buffer pool.
   const size_t attributes_size = 3;
   CFTypeRef keys[attributes_size] = {
 #if defined(WEBRTC_IOS)
@@ skipping 203 matching lines @@
   }
   bitrate_adjuster_.Update(frame._length);
 }
 
 VideoEncoder::ScalingSettings H264VideoToolboxEncoder::GetScalingSettings()
     const {
   return VideoEncoder::ScalingSettings(true, internal::kLowH264QpThreshold,
                                        internal::kHighH264QpThreshold);
 }
 }  // namespace webrtc