3 files changed, 13 insertions, 9 deletions

diff --git a/src/audio_core/sink/null_sink.h b/src/audio_core/sink/null_sink.h
index 1215d3cd2..b6b43c93e 100644
--- a/src/audio_core/sink/null_sink.h
+++ b/src/audio_core/sink/null_sink.h
@@ -20,7 +20,7 @@ public:
     explicit NullSinkStreamImpl(Core::System& system_, StreamType type_)
         : SinkStream{system_, type_} {}
     ~NullSinkStreamImpl() override {}
-    void AppendBuffer(SinkBuffer&, std::vector<s16>&) override {}
+    void AppendBuffer(SinkBuffer&, std::span<s16>) override {}
     std::vector<s16> ReleaseBuffer(u64) override {
         return {};
     }
diff --git a/src/audio_core/sink/sink_stream.cpp b/src/audio_core/sink/sink_stream.cpp
index 9a718a9cc..404dcd0e9 100644
--- a/src/audio_core/sink/sink_stream.cpp
+++ b/src/audio_core/sink/sink_stream.cpp
@@ -18,7 +18,7 @@
 
 namespace AudioCore::Sink {
 
-void SinkStream::AppendBuffer(SinkBuffer& buffer, std::vector<s16>& samples) {
+void SinkStream::AppendBuffer(SinkBuffer& buffer, std::span<s16> samples) {
     if (type == StreamType::In) {
         queue.enqueue(buffer);
         queued_buffers++;
@@ -66,15 +66,16 @@ void SinkStream::AppendBuffer(SinkBuffer& buffer, std::vector<s16>& samples) {
                 static_cast<s16>(std::clamp(right_sample, min, max));
         }
 
-        samples.resize(samples.size() / system_channels * device_channels);
+        samples = samples.subspan(0, samples.size() / system_channels * device_channels);
 
     } else if (system_channels == 2 && device_channels == 6) {
         // We need moar samples! Not all games will provide 6 channel audio.
         // TODO: Implement some upmixing here. Currently just passthrough, with other
         // channels left as silence.
-        std::vector<s16> new_samples(samples.size() / system_channels * device_channels, 0);
+        auto new_size = samples.size() / system_channels * device_channels;
+        tmp_samples.resize_destructive(new_size);
 
-        for (u32 read_index = 0, write_index = 0; read_index < samples.size();
+        for (u32 read_index = 0, write_index = 0; read_index < new_size;
              read_index += system_channels, write_index += device_channels) {
             const auto left_sample{static_cast<s16>(std::clamp(
                 static_cast<s32>(
@@ -82,7 +83,7 @@ void SinkStream::AppendBuffer(SinkBuffer& buffer, std::vector<s16>& samples) {
                     volume),
                 min, max))};
 
-            new_samples[write_index + static_cast<u32>(Channels::FrontLeft)] = left_sample;
+            tmp_samples[write_index + static_cast<u32>(Channels::FrontLeft)] = left_sample;
 
             const auto right_sample{static_cast<s16>(std::clamp(
                 static_cast<s32>(
@@ -90,9 +91,9 @@ void SinkStream::AppendBuffer(SinkBuffer& buffer, std::vector<s16>& samples) {
                     volume),
                 min, max))};
 
-            new_samples[write_index + static_cast<u32>(Channels::FrontRight)] = right_sample;
+            tmp_samples[write_index + static_cast<u32>(Channels::FrontRight)] = right_sample;
         }
-        samples = std::move(new_samples);
+        samples = std::span<s16>(tmp_samples);
 
     } else if (volume != 1.0f) {
         for (u32 i = 0; i < samples.size(); i++) {
diff --git a/src/audio_core/sink/sink_stream.h b/src/audio_core/sink/sink_stream.h
index 41cbadc9c..98d72ace1 100644
--- a/src/audio_core/sink/sink_stream.h
+++ b/src/audio_core/sink/sink_stream.h
@@ -16,6 +16,7 @@
 #include "common/polyfill_thread.h"
 #include "common/reader_writer_queue.h"
 #include "common/ring_buffer.h"
+#include "common/scratch_buffer.h"
 #include "common/thread.h"
 
 namespace Core {
@@ -170,7 +171,7 @@ public:
      * @param buffer  - Audio buffer information to be queued.
      * @param samples - The s16 samples to be queue for playback.
      */
-    virtual void AppendBuffer(SinkBuffer& buffer, std::vector<s16>& samples);
+    virtual void AppendBuffer(SinkBuffer& buffer, std::span<s16> samples);
 
     /**
      * Release a buffer. Audio In only, will fill a buffer with recorded samples.
@@ -255,6 +256,8 @@ private:
     /// Signalled when ring buffer entries are consumed
     std::condition_variable_any release_cv;
     std::mutex release_mutex;
+    /// Temporary buffer for appending samples when upmixing
+    Common::ScratchBuffer<s16> tmp_samples{};
 };
 
 using SinkStreamPtr = std::unique_ptr<SinkStream>;