Create a null decoder for h264 when not supported, instead of crashing.

webrtc/video/video_decoder.cc

 /*
  *  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.
  */
 
 #include "webrtc/video_decoder.h"
 
 #include "webrtc/base/checks.h"
 #include "webrtc/base/logging.h"
 #include "webrtc/modules/video_coding/codecs/h264/include/h264.h"
 #include "webrtc/modules/video_coding/codecs/vp8/include/vp8.h"
 #include "webrtc/modules/video_coding/codecs/vp9/include/vp9.h"
 
 namespace webrtc {
 VideoDecoder* VideoDecoder::Create(VideoDecoder::DecoderType codec_type) {
   switch (codec_type) {
     case kH264:
+      if (!H264Decoder::IsSupported()) {
+        // This could happen in a software-fallback for a codec type only
+        // supported externally (e.g. H.264 on iOS or Android) or in current
+        // usage in WebRtcVideoEngine2 if the external decoder fails to be
+        // created.
+        LOG(LS_ERROR) << "Unable to create a software H.264 decoder. "
+                      << "Decoding of this stream will be broken.";
+        return new NullVideoDecoder();
+      }
       RTC_DCHECK(H264Decoder::IsSupported());

[pbos-webrtc, 2016/06/26 19:15:59]

Remove this DCHECK.

[noahric, 2016/06/27 23:15:02]

Done. Also changed the log line slightly, since it may not be a software
fallback as written (H264Decoder::Create would create a hardware backed decoder
on e.g. iOS).

       return H264Decoder::Create();
     case kVp8:
       return VP8Decoder::Create();
     case kVp9:
       RTC_DCHECK(VP9Decoder::IsSupported());
       return VP9Decoder::Create();
     case kUnsupportedCodec:
       LOG(LS_ERROR) << "Creating NullVideoDecoder for unsupported codec.";
       return new NullVideoDecoder();
   }
@@ skipping 133 matching lines @@
 
 int32_t NullVideoDecoder::Release() {
   return WEBRTC_VIDEO_CODEC_OK;
 }
 
 const char* NullVideoDecoder::ImplementationName() const {
   return "NullVideoDecoder";
 }
 
 }  // namespace webrtc