Make AV1X constants private

The constants are being made private since no new code should use them.
However, the helper functions sill uses "AV1X" internally for backwards
compatibility.

Bug: webrtc:13166
Change-Id: I0a0cd46f31ca70bb7f395c9b1e9cdb202df11f6e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/236680
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Sergey Silkin <ssilkin@webrtc.org>
Commit-Queue: Emil Lundmark <lndmrk@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35289}
diff --git a/api/video_codecs/video_codec.cc b/api/video_codecs/video_codec.cc
index e96a63a..d850917 100644
--- a/api/video_codecs/video_codec.cc
+++ b/api/video_codecs/video_codec.cc
@@ -22,7 +22,8 @@
 constexpr char kPayloadNameVp8[] = "VP8";
 constexpr char kPayloadNameVp9[] = "VP9";
 constexpr char kPayloadNameAv1[] = "AV1";
-// TODO(bugs.webrtc.org/13166): Delete after all dependent projects updated.
+// TODO(bugs.webrtc.org/13166): Remove AV1X when backwards compatibility is not
+// needed.
 constexpr char kPayloadNameAv1x[] = "AV1X";
 constexpr char kPayloadNameH264[] = "H264";
 constexpr char kPayloadNameGeneric[] = "Generic";
diff --git a/media/base/media_constants.cc b/media/base/media_constants.cc
index 83be53a..da5e7a8 100644
--- a/media/base/media_constants.cc
+++ b/media/base/media_constants.cc
@@ -103,7 +103,6 @@
 const char kVp8CodecName[] = "VP8";
 const char kVp9CodecName[] = "VP9";
 const char kAv1CodecName[] = "AV1";
-const char kAv1xCodecName[] = "AV1X";
 const char kH264CodecName[] = "H264";
 
 // RFC 6184 RTP Payload Format for H.264 video
diff --git a/media/base/media_constants.h b/media/base/media_constants.h
index 313b0f8..16c5db9 100644
--- a/media/base/media_constants.h
+++ b/media/base/media_constants.h
@@ -123,8 +123,6 @@
 RTC_EXPORT extern const char kVp8CodecName[];
 RTC_EXPORT extern const char kVp9CodecName[];
 RTC_EXPORT extern const char kAv1CodecName[];
-// TODO(bugs.webrtc.org/13166): Delete after all dependent projects updated.
-RTC_EXPORT extern const char kAv1xCodecName[];
 RTC_EXPORT extern const char kH264CodecName[];
 
 // RFC 6184 RTP Payload Format for H.264 video
diff --git a/media/engine/webrtc_video_engine.cc b/media/engine/webrtc_video_engine.cc
index bdce2ba..359cbd3 100644
--- a/media/engine/webrtc_video_engine.cc
+++ b/media/engine/webrtc_video_engine.cc
@@ -53,6 +53,10 @@
 const int kMinLayerSize = 16;
 constexpr int64_t kUnsignaledSsrcCooldownMs = rtc::kNumMillisecsPerSec / 2;
 
+// TODO(bugs.webrtc.org/13166): Remove AV1X when backwards compatibility is not
+// needed.
+constexpr char kAv1xCodecName[] = "AV1X";
+
 const char* StreamTypeToString(
     webrtc::VideoSendStream::StreamStats::StreamType type) {
   switch (type) {