Allow software fallback on lowest simulcast stream for temporal support

Bug: webrtc:11324
Change-Id: Ie505be0cda74c0444065d86c3727671c62bd4842
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/167527
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Evan Shrubsole <eshr@google.com>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Commit-Queue: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30437}

api/video_codecs/video_encoder_software_fallback_wrapper.h

@@ -12,6 +12,7 @@
 #define API_VIDEO_CODECS_VIDEO_ENCODER_SOFTWARE_FALLBACK_WRAPPER_H_
 
 #include <memory>
+#include <utility>
 
 #include "api/video_codecs/video_encoder.h"
 #include "rtc_base/system/rtc_export.h"
@@ -21,10 +22,25 @@ namespace webrtc {
 // Used to wrap external VideoEncoders to provide a fallback option on
 // software encoding when a hardware encoder fails to encode a stream due to
 // hardware restrictions, such as max resolution.
+// |bool prefer_temporal_support| indicates that if the software fallback
+// encoder supports temporal layers but the hardware encoder does not, a
+// fallback should be forced even if the encoder otherwise works.
 RTC_EXPORT std::unique_ptr<VideoEncoder>
 CreateVideoEncoderSoftwareFallbackWrapper(
     std::unique_ptr<VideoEncoder> sw_fallback_encoder,
-    std::unique_ptr<VideoEncoder> hw_encoder);
+    std::unique_ptr<VideoEncoder> hw_encoder,
+    bool prefer_temporal_support);
+
+// Default fallback for call-sites not yet updated with
+// |prefer_temporal_support|.
+// TODO(sprang): Remove when usage is gone.
+RTC_EXPORT inline std::unique_ptr<VideoEncoder>
+CreateVideoEncoderSoftwareFallbackWrapper(
+    std::unique_ptr<VideoEncoder> sw_fallback_encoder,
+    std::unique_ptr<VideoEncoder> hw_encoder) {
+  return CreateVideoEncoderSoftwareFallbackWrapper(
+      std::move(sw_fallback_encoder), std::move(hw_encoder), false);
+}
 
 }  // namespace webrtc