4 files changed, 66 insertions, 5 deletions
diff --git a/src/codecs/include/codec.hpp b/src/codecs/include/codec.hpp
index e8be8f0a..f260aca4 100644
--- a/src/codecs/include/codec.hpp
+++ b/src/codecs/include/codec.hpp
@@ -16,6 +16,7 @@
 #include <string>
 #include <utility>
 
+#include "sample.hpp"
 #include "result.hpp"
 #include "span.hpp"
 #include "types.hpp"
@@ -61,7 +62,6 @@ class ICodec {
 
   struct OutputFormat {
     uint8_t num_channels;
-    uint8_t bits_per_sample;
     uint32_t sample_rate_hz;
 
     std::optional<uint32_t> duration_seconds;
@@ -76,7 +76,7 @@ class ICodec {
       -> Result<OutputFormat> = 0;
 
   struct OutputInfo {
-    std::size_t bytes_written;
+    std::size_t samples_written;
     bool is_finished_writing;
   };
 
@@ -84,7 +84,7 @@ class ICodec {
    * Writes PCM samples to the given output buffer.
    */
   virtual auto ContinueStream(cpp::span<const std::byte> input,
-                              cpp::span<std::byte> output)
+                              cpp::span<sample::Sample> output)
       -> Result<OutputInfo> = 0;
 
   virtual auto SeekStream(cpp::span<const std::byte> input,
diff --git a/src/codecs/include/foxenflac.hpp b/src/codecs/include/foxenflac.hpp
index cce1b762..abfa6d80 100644
--- a/src/codecs/include/foxenflac.hpp
+++ b/src/codecs/include/foxenflac.hpp
@@ -14,6 +14,7 @@
 #include <utility>
 
 #include "foxen/flac.h"
+#include "sample.hpp"
 #include "span.hpp"
 
 #include "codec.hpp"
@@ -26,7 +27,7 @@ class FoxenFlacDecoder : public ICodec {
   ~FoxenFlacDecoder();
 
   auto BeginStream(cpp::span<const std::byte>) -> Result<OutputFormat> override;
-  auto ContinueStream(cpp::span<const std::byte>, cpp::span<std::byte>)
+  auto ContinueStream(cpp::span<const std::byte>, cpp::span<sample::Sample>)
       -> Result<OutputInfo> override;
   auto SeekStream(cpp::span<const std::byte> input, std::size_t target_sample)
       -> Result<void> override;
diff --git a/src/codecs/include/mad.hpp b/src/codecs/include/mad.hpp
index fbae560c..b81e4acb 100644
--- a/src/codecs/include/mad.hpp
+++ b/src/codecs/include/mad.hpp
@@ -13,6 +13,7 @@
 #include <utility>
 
 #include "mad.h"
+#include "sample.hpp"
 #include "span.hpp"
 
 #include "codec.hpp"
@@ -35,7 +36,7 @@ class MadMp3Decoder : public ICodec {
    * Writes samples for the current frame.
    */
   auto ContinueStream(cpp::span<const std::byte> input,
-                      cpp::span<std::byte> output)
+                      cpp::span<sample::Sample> output)
       -> Result<OutputInfo> override;
 
   auto SeekStream(cpp::span<const std::byte> input, std::size_t target_sample)
diff --git a/src/codecs/include/sample.hpp b/src/codecs/include/sample.hpp
new file mode 100644
index 00000000..7209673b
--- /dev/null
+++ b/src/codecs/include/sample.hpp
@@ -0,0 +1,59 @@
+#pragma once
+
+#include <stdint.h>
+
+#include <algorithm>
+
+#include <mad.h>
+
+namespace sample {
+
+// A signed, 32-bit PCM sample.
+typedef int32_t Sample;
+
+constexpr auto Clip(int64_t v) -> Sample {
+  if (v > INT32_MAX)
+    return INT32_MAX;
+  if (v < INT32_MIN)
+    return INT32_MIN;
+  return v;
+}
+
+constexpr auto FromSigned(int32_t src, uint_fast8_t bits) -> Sample {
+  // Left-align samples, effectively scaling them up to 32 bits.
+  return src << (sizeof(Sample) * 8 - bits);
+}
+
+constexpr auto FromUnsigned(uint32_t src, uint_fast8_t bits) -> Sample {
+  // Left-align, then substract the max value / 2 to make the sample centred
+  // around zero.
+  return (src << (sizeof(uint32_t) * 8 - bits)) - (~0UL >> 1);
+}
+
+constexpr auto FromFloat(float src) -> Sample {
+  return std::clamp<float>(src, -1.0f, 1.0f) * static_cast<float>(INT32_MAX);
+}
+
+constexpr auto FromDouble(double src) -> Sample {
+  return std::clamp<double>(src, -1.0, 1.0) * static_cast<double>(INT32_MAX);
+}
+
+constexpr auto FromMad(mad_fixed_t src) -> Sample {
+  // Round the bottom bits.
+  src += (1L << (MAD_F_FRACBITS - 24));
+
+  // Clip the leftover bits to within range.
+  if (src >= MAD_F_ONE)
+    src = MAD_F_ONE - 1;
+  else if (src < -MAD_F_ONE)
+    src = -MAD_F_ONE;
+
+  // Quantize.
+  return FromSigned(src >> (MAD_F_FRACBITS + 1 - 24), 24);
+}
+
+constexpr auto ToSigned16Bit(Sample src) -> uint16_t {
+  return src >> 16;
+}
+
+}  // namespace sample