third_party/iamf_tools (new in 153) includes the vendored copy of Opus via
relative "include/opus.h"-style paths that only resolve when
//third_party/opus/src is the real bundled Opus checkout. With Opus
unbundled (system libopus via build/linux/unbundle/opus.gn's shim_headers
target), that directory doesn't contain a real "include/" subtree, so the
compile fails with:

  fatal error: 'include/opus.h' file not found

Use the same full "third_party/opus/src/include/..." style path that other
in-tree consumers (e.g. third_party/opus/tests/opus_benchmark.cc) use, which
resolves correctly against both the shim headers and a real bundled Opus
checkout, since root src is always on the include path.

--- a/third_party/iamf_tools/src/iamf/cli/codec/opus_decoder.cc
+++ b/third_party/iamf_tools/src/iamf/cli/codec/opus_decoder.cc
@@ -30,8 +30,8 @@
 #include "iamf/obu/decoder_config/opus_decoder_config.h"
 #include "iamf/obu/substream_channel_count.h"
 #include "iamf/obu/types.h"
-#include "include/opus.h"
-#include "include/opus_types.h"
+#include "third_party/opus/src/include/opus.h"
+#include "third_party/opus/src/include/opus_types.h"

 namespace iamf_tools {

--- a/third_party/iamf_tools/src/iamf/cli/codec/opus_decoder.h
+++ b/third_party/iamf_tools/src/iamf/cli/codec/opus_decoder.h
@@ -23,7 +23,7 @@
 #include "iamf/cli/codec/decoder_base.h"
 #include "iamf/obu/decoder_config/opus_decoder_config.h"
 #include "iamf/obu/substream_channel_count.h"
-#include "include/opus.h"
+#include "third_party/opus/src/include/opus.h"

 namespace iamf_tools {

--- a/third_party/iamf_tools/src/iamf/cli/codec/opus_encoder.cc
+++ b/third_party/iamf_tools/src/iamf/cli/codec/opus_encoder.cc
@@ -32,9 +32,9 @@
 #include "iamf/common/utils/validation_utils.h"
 #include "iamf/obu/decoder_config/opus_decoder_config.h"
 #include "iamf/obu/substream_channel_count.h"
-#include "include/opus.h"
-#include "include/opus_defines.h"
-#include "include/opus_types.h"
+#include "third_party/opus/src/include/opus.h"
+#include "third_party/opus/src/include/opus_defines.h"
+#include "third_party/opus/src/include/opus_types.h"

 namespace iamf_tools {

--- a/third_party/iamf_tools/src/iamf/cli/codec/opus_encoder.h
+++ b/third_party/iamf_tools/src/iamf/cli/codec/opus_encoder.h
@@ -22,8 +22,8 @@
 #include "iamf/obu/codec_config.h"
 #include "iamf/obu/decoder_config/opus_decoder_config.h"
 #include "iamf/obu/substream_channel_count.h"
-#include "include/opus.h"
-#include "include/opus_defines.h"
+#include "third_party/opus/src/include/opus.h"
+#include "third_party/opus/src/include/opus_defines.h"

 namespace iamf_tools {

--- a/third_party/iamf_tools/src/iamf/cli/codec/opus_utils.cc
+++ b/third_party/iamf_tools/src/iamf/cli/codec/opus_utils.cc
@@ -3,7 +3,7 @@
 #include "absl/status/status.h"
 #include "absl/strings/str_cat.h"
 #include "absl/strings/string_view.h"
-#include "include/opus_defines.h"
+#include "third_party/opus/src/include/opus_defines.h"

 namespace iamf_tools {