separated decoder retrieve functions for video and audio

It became increasingly clear that video and audio retrieval require different
parameters so it started to make sense to separate these functions out.

app/decoder/decoder.cpp

@@ -55,6 +55,26 @@ void Decoder::set_stream(StreamPtr fs)
   stream_ = fs;
 }
 
+FramePtr Decoder::RetrieveVideo(const rational &/*timecode*/)
+{
+  return nullptr;
+}
+
+FramePtr Decoder::RetrieveAudio(const rational &/*timecode*/, const rational &/*length*/, const AudioRenderingParams &/*params*/)
+{
+  return nullptr;
+}
+
+bool Decoder::SupportsVideo()
+{
+  return false;
+}
+
+bool Decoder::SupportsAudio()
+{
+  return false;
+}
+
 /*
  * DECODER STATIC PUBLIC MEMBERS
  */

app/decoder/decoder.h

@@ -107,10 +107,33 @@ public:
   virtual bool Open() = 0;
 
   /**
-   * @brief Retrieve frame/data
+   * @brief Retrieve video frame
    *
-   * The main function for retrieving data from the Decoder. This function should always provide complete frame data
-   * (i.e. no partial frames or missing samples) at the timecode provided. The Decoder should perform any steps
+   * The main function for retrieving video data from the Decoder. This function should always provide complete frame
+   * data (i.e. no partial frames) at the timecode provided. The Decoder should perform any steps required to retrieve
+   * a complete frame separate from the rest of the program, using any form of caching/indexing to keep this as
+   * performant as possible.
+   *
+   * It's acceptable for this function to check whether the Decoder is open, and call Open() if not. If Open() returns
+   * false, this function should return nullptr.
+   *
+   * @param timecode
+   *
+   * The timecode (a rational in seconds) to retrieve the frame at. If there is not a frame at this precise location
+   * this should be corrected internally to the closest fit for the timecode.
+   *
+   * @return
+   *
+   * A FramePtr of valid data at this timecode or nullptr if there was nothing to retrieve at the provided timecode or
+   * the media could not be opened.
+   */
+  virtual FramePtr RetrieveVideo(const rational& timecode);
+
+  /**
+   * @brief Retrieve video frame
+   *
+   * The main function for retrieving audio data from the Decoder. This function should always provide complete frame
+   * data (i.e. no missing samples) at the timecode and length requested. The Decoder should perform any steps
    * required to retrieve a complete frame separate from the rest of the program, using any form of caching/indexing
    * to keep this as performant as possible.
    *
@@ -119,18 +142,21 @@ public:
    *
    * @param timecode
    *
-   * The timecode (a rational in seconds) to retrieve the data at.
+   * The starting timecode (a rational in seconds) to retrieve the data at.
    *
    * @param length
    *
-   * Audio only - ignored for video decoders. The total length of audio data to retrieve (a rational in seconds).
+   * The total length of audio data to retrieve (a rational in seconds).
    *
    * @return
    *
-   * A FramePtr of valid data at this timecode (of the requested length if this is audio media), or nullptr if there
-   * was nothing to retrieve at the provided timecode or the media could not be opened.
+   * A FramePtr of valid data at this timecode of the requested length or nullptr if there was nothing to retrieve at
+   * the provided timecode or the media could not be opened.
    */
-  virtual FramePtr Retrieve(const rational& timecode, const rational& length = 0) = 0;
+  virtual FramePtr RetrieveAudio(const rational& timecode, const rational& length, const AudioRenderingParams& params);
+
+  virtual bool SupportsVideo();
+  virtual bool SupportsAudio();
 
   /**
    * @brief Close media/deallocate memory