Upstream Gentoo Linux patch for using system ffmpeg

media/ffmpeg/ffmpeg_common.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_FFMPEG_FFMPEG_COMMON_H_
 #define MEDIA_FFMPEG_FFMPEG_COMMON_H_
 
 #include <stdint.h>
 #include <string>
 
 // Used for FFmpeg error codes.
 #include <cerrno>
 
 #include "base/compiler_specific.h"
 #include "base/time/time.h"
 #include "media/base/audio_codecs.h"
 #include "media/base/channel_layout.h"
 #include "media/base/media_export.h"
 #include "media/base/sample_format.h"
 #include "media/base/video_codecs.h"
 #include "media/base/video_frame.h"
 #include "media/ffmpeg/ffmpeg_deleters.h"
 
 // Include FFmpeg header files.
 extern "C" {
+#if !defined(USE_SYSTEM_FFMPEG)
 // Disable deprecated features which result in spammy compile warnings.  This
 // list of defines must mirror those in the 'defines' section of FFmpeg's
 // BUILD.gn file or the headers below will generate different structures!
 #define FF_API_CONVERGENCE_DURATION 0
+#endif  // !defined(USE_SYSTEM_FFMPEG)
 // Upstream libavcodec/utils.c still uses the deprecated
 // av_dup_packet(), causing deprecation warnings.
 // The normal fix for such things is to disable the feature as below,
 // but the upstream code does not yet compile with it disabled.
 // (In this case, the fix is replacing the call with a new function.)
 // In the meantime, we directly disable those warnings in the C file.
 //#define FF_API_AVPACKET_OLD_API 0
 
 // Temporarily disable possible loss of data warning.
 // TODO(scherkus): fix and upstream the compiler warnings.
 MSVC_PUSH_DISABLE_WARNING(4244);
 #include <libavcodec/avcodec.h>
 #include <libavformat/avformat.h>
+#if !defined(USE_SYSTEM_FFMPEG)
 #include <libavformat/internal.h>
+#endif  // !defined(USE_SYSTEM_FFMPEG)
 #include <libavformat/avio.h>
 #include <libavutil/avutil.h>
 #include <libavutil/imgutils.h>
 #include <libavutil/log.h>
 #include <libavutil/mathematics.h>
 #include <libavutil/opt.h>
 MSVC_POP_WARNING();
 }  // extern "C"
 
 namespace media {
@@ skipping 100 matching lines @@
 // Converts an AVERROR error number to a description.
 std::string AVErrorToString(int errnum);
 
 // Returns a 32-bit hash for the given codec name.  See the VerifyUmaCodecHashes
 // unit test for more information and code for generating the histogram XML.
 MEDIA_EXPORT int32_t HashCodecName(const char* codec_name);
 
 }  // namespace media
 
 #endif  // MEDIA_FFMPEG_FFMPEG_COMMON_H_