Fix regression for h264 VideoToolbox entering background.

webrtc/modules/video_coding/codecs/h264/h264_video_toolbox_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 289 matching lines @@
       GetScaledBufferOnEncode(frame.video_frame_buffer()));
 
   if (input_image->width() != width_ || input_image->height() != height_) {
     width_ = input_image->width();
     height_ = input_image->height();
     int ret = ResetCompressionSession();
     if (ret < 0)
       return ret;
   }
 
+  // Get a pixel buffer from the pool and copy frame data over.
+  CVPixelBufferPoolRef pixel_buffer_pool =
+      VTCompressionSessionGetPixelBufferPool(compression_session_);
+#if defined(WEBRTC_IOS)
+  if (!pixel_buffer_pool) {
+    // Kind of a hack. On backgrounding, the compression session seems to get
+    // invalidated, which causes this pool call to fail when the application
+    // is foregrounded and frames are being sent for encoding again.
+    // Resetting the session when this happens fixes the issue.
+    // In addition we request a keyframe so video can recover quickly.
+    ResetCompressionSession();
+    pixel_buffer_pool =
+        VTCompressionSessionGetPixelBufferPool(compression_session_);
+    is_keyframe_required = true;
+    LOG(LS_INFO) << "Resetting compression session due to invalid pool.";
+  }
+#endif
+
   CVPixelBufferRef pixel_buffer =
       static_cast<CVPixelBufferRef>(input_image->native_handle());
   if (pixel_buffer) {
     CVBufferRetain(pixel_buffer);
+    pixel_buffer_pool = nullptr;
   } else {
-    // Get a pixel buffer from the pool and copy frame data over.
-    CVPixelBufferPoolRef pixel_buffer_pool =
-        VTCompressionSessionGetPixelBufferPool(compression_session_);
-#if defined(WEBRTC_IOS)
-    if (!pixel_buffer_pool) {
-      // Kind of a hack. On backgrounding, the compression session seems to get
-      // invalidated, which causes this pool call to fail when the application
-      // is foregrounded and frames are being sent for encoding again.
-      // Resetting the session when this happens fixes the issue.
-      // In addition we request a keyframe so video can recover quickly.
-      ResetCompressionSession();
-      pixel_buffer_pool =
-          VTCompressionSessionGetPixelBufferPool(compression_session_);
-      is_keyframe_required = true;
-    }
-#endif
     if (!pixel_buffer_pool) {
       LOG(LS_ERROR) << "Failed to get pixel buffer pool.";
       return WEBRTC_VIDEO_CODEC_ERROR;
     }
     CVReturn ret = CVPixelBufferPoolCreatePixelBuffer(
         nullptr, pixel_buffer_pool, &pixel_buffer);
     if (ret != kCVReturnSuccess) {
       LOG(LS_ERROR) << "Failed to create pixel buffer: " << ret;
       // We probably want to drop frames here, since failure probably means
       // that the pool is empty.
@@ skipping 300 matching lines @@
   if (result != 0) {
     LOG(LS_ERROR) << "Encode callback failed: " << result;
     return;
   }
   bitrate_adjuster_.Update(frame._size);
 }
 
 }  // namespace webrtc
 
 #endif  // defined(WEBRTC_VIDEO_TOOLBOX_SUPPORTED)