Add vorbis and flac decoders, flesh out codec interface

vorbis doesn't quite work yet, not sure why. will pick it up again
later.

1 files changed, 35 insertions, 25 deletions

diff --git a/src/codecs/include/codec.hpp b/src/codecs/include/codec.hpp
index 31c67e13..4b5ab47f 100644
--- a/src/codecs/include/codec.hpp
+++ b/src/codecs/include/codec.hpp
@@ -21,48 +21,58 @@
 
 namespace codecs {
 
+/*
+ * Common interface to be implemented by all audio decoders.
+ */
 class ICodec {
  public:
   virtual ~ICodec() {}
 
+  /* Errors that may be returned by codecs. */
+  enum class Error {
+    // Indicates that more data is required before this codec can finish its
+    // operation. E.g. the input buffer ends with a truncated frame.
+    kOutOfInput,
+    // Indicates that the data within the input buffer is fatally malformed.
+    kMalformedData,
+
+    kInternalError,
+  };
+
+  /*
+   * Alias for more readable return types. All codec methods, success or
+   * failure, should also return the number of bytes they consumed.
+   */
+  template <typename T>
+  using Result = std::pair<std::size_t, cpp::result<T, Error>>;
+
   struct OutputFormat {
     uint8_t num_channels;
     uint8_t bits_per_sample;
     uint32_t sample_rate_hz;
   };
 
-  virtual auto GetOutputFormat() -> std::optional<OutputFormat> = 0;
-
-  enum ProcessingError { MALFORMED_DATA };
-
-  virtual auto SetInput(cpp::span<const std::byte> input) -> void = 0;
-
   /*
-   * Returns the codec's next read position within the input buffer. If the
-   * codec is out of usable data, but there is still some data left in the
-   * stream, that data should be prepended to the next input buffer.
+   * Decodes metadata or headers from the given input stream, and returns the
+   * format for the samples that will be decoded from it.
    */
-  virtual auto GetInputPosition() -> std::size_t = 0;
+  virtual auto BeginStream(cpp::span<const std::byte> input)
+      -> Result<OutputFormat> = 0;
 
-  /*
-   * Read one frame (or equivalent discrete chunk) from the input, and
-   * synthesize output samples for it.
-   *
-   * Returns true if we are out of usable data from the input stream, or false
-   * otherwise.
-   */
-  virtual auto ProcessNextFrame() -> cpp::result<bool, ProcessingError> = 0;
+  struct OutputInfo {
+    std::size_t bytes_written;
+    bool is_finished_writing;
+  };
 
   /*
    * Writes PCM samples to the given output buffer.
-   *
-   * Returns the number of bytes that were written, and true if all of the
-   * samples synthesized from the last call to `ProcessNextFrame` have been
-   * written. If this returns false, then this method should be called again
-   * after flushing the output buffer.
    */
-  virtual auto WriteOutputSamples(cpp::span<std::byte> output)
-      -> std::pair<std::size_t, bool> = 0;
+  virtual auto ContinueStream(cpp::span<const std::byte> input,
+                              cpp::span<std::byte> output)
+      -> Result<OutputInfo> = 0;
+
+  virtual auto SeekStream(cpp::span<const std::byte> input,
+                          std::size_t target_sample) -> Result<void> = 0;
 };
 
 auto CreateCodecForType(StreamType type) -> std::optional<ICodec*>;