Ensure video frame buffer is still decodable before decoding

This ensures that if for some reason, the frame buffer becomes
undecodable while waiting to decode a frame, the decoding is halted.
This also guards against receiving an empty temporal unit from the frame
buffer, even though this should never happen when the frame buffer has a
decodable temporal unit.

Bug: chromium:1378253, chromium:1361623
Change-Id: I8c4c897bf474d5cbda5f0f357781bf1dc0701fe4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/280701
Commit-Queue: Evan Shrubsole <eshr@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38494}

video/video_stream_buffer_controller.cc

diff --git a/video/video_stream_buffer_controller.cc b/video/video_stream_buffer_controller.cc
index 0e0f2cc..f7d3acd 100644
--- a/video/video_stream_buffer_controller.cc
+++ b/video/video_stream_buffer_controller.cc
@@ -191,7 +191,8 @@
     absl::InlinedVector<std::unique_ptr<EncodedFrame>, 4> frames,
     Timestamp render_time) {
   RTC_DCHECK_RUN_ON(&worker_sequence_checker_);
-  RTC_DCHECK(!frames.empty());
+  RTC_CHECK(!frames.empty())
+      << "Callers must ensure there is at least one frame to decode.";
 
   timeout_tracker_.OnEncodedFrameReleased();
 
@@ -275,11 +276,29 @@
 void VideoStreamBufferController::FrameReadyForDecode(uint32_t rtp_timestamp,
                                                       Timestamp render_time) {
   RTC_DCHECK_RUN_ON(&worker_sequence_checker_);
-  auto frames = buffer_->ExtractNextDecodableTemporalUnit();
-  RTC_DCHECK(frames[0]->Timestamp() == rtp_timestamp)
+  // Check that the frame to decode is still valid before passing the frame for
+  // decoding.
+  auto decodable_tu_info = buffer_->DecodableTemporalUnitsInfo();
+  if (!decodable_tu_info) {
+    RTC_LOG(LS_ERROR)
+        << "The frame buffer became undecodable during the wait "
+           "to decode frame with rtp-timestamp "
+        << rtp_timestamp
+        << ". Cancelling the decode of this frame, decoding "
+           "will resume when the frame buffers become decodable again.";
+    return;
+  }
+  RTC_DCHECK_EQ(rtp_timestamp, decodable_tu_info->next_rtp_timestamp)
       << "Frame buffer's next decodable frame was not the one sent for "
-         "extraction rtp="
-      << rtp_timestamp << " extracted rtp=" << frames[0]->Timestamp();
+         "extraction.";
+  auto frames = buffer_->ExtractNextDecodableTemporalUnit();
+  if (frames.empty()) {
+    RTC_LOG(LS_ERROR)
+        << "The frame buffer should never return an empty temporal until list "
+           "when there is a decodable temporal unit.";
+    RTC_DCHECK_NOTREACHED();
+    return;
+  }
   OnFrameReady(std::move(frames), render_time);
 }