Add StreamReader/Writer custom IO to doc (#3367)

Summary: Pull Request resolved: https://github.com/pytorch/audio/pull/3367

Reviewed By: nateanl

Differential Revision: D46148139

Pulled By: mthrok

fbshipit-source-id: 50f297ac69bb95562976eb452e4e382b8c064c3c

docs/source/libtorchaudio.stream_reader.rst

@@ -5,13 +5,28 @@
 torchaudio::io::StreamReader
 ============================
 
-.. doxygenclass:: torchaudio::io::StreamReader
+``StreamReader`` is the implementation used by Python equivalent and provides similar interface.
+When working with custom I/O, such as in-memory data, ``StreamReaderCustomIO`` class can be used.
+
+Both classes have the same methods defined, so their usages are the same.
 
 Constructors
 ------------
 
+StreamReader
+^^^^^^^^^^^^
+
+.. doxygenclass:: torchaudio::io::StreamReader
+
 .. doxygenfunction:: torchaudio::io::StreamReader::StreamReader(const std::string &src, const c10::optional<std::string> &format = {}, const c10::optional<OptionDict> &option = {})
 
+StreamReaderCustomIO
+^^^^^^^^^^^^^^^^^^^^
+
+.. doxygenclass:: torchaudio::io::StreamReaderCustomIO
+
+.. doxygenfunction:: torchaudio::io::StreamReaderCustomIO::StreamReaderCustomIO
+
 Query Methods
 -------------
 

docs/source/libtorchaudio.stream_writer.rst

@@ -5,13 +5,28 @@
 torchaudio::io::StreamWriter
 ============================
 
-.. doxygenclass:: torchaudio::io::StreamWriter
+``StreamWriter`` is the implementation used by Python equivalent and provides similar interface.
+When working with custom I/O, such as in-memory data, ``StreamWriterCustomIO`` class can be used.
+
+Both classes have the same methods defined, so their usages are the same.
 
 Constructors
 ------------
 
+StreamWriter
+^^^^^^^^^^^^
+
+.. doxygenclass:: torchaudio::io::StreamWriter
+
 .. doxygenfunction:: torchaudio::io::StreamWriter::StreamWriter(const std::string &dst, const c10::optional<std::string> &format = {})
 
+StreamWriterCustomIO
+^^^^^^^^^^^^^^^^^^^^
+
+.. doxygenclass:: torchaudio::io::StreamWriterCustomIO
+
+.. doxygenfunction:: torchaudio::io::StreamWriterCustomIO::StreamWriterCustomIO
+
 Config methods
 --------------
 

torchaudio/csrc/ffmpeg/stream_reader/stream_reader.h

@@ -359,16 +359,23 @@ struct CustomInput {
 
 /// @endcond
 
-/// Construct StreamReader with custom read and seek functions.
 ///
-/// @param opaque Custom data used by read_packet and seek functions.
-/// @param format Specify input format.
-/// @param buffer_size The size of the intermediate buffer, which FFmpeg uses to
-/// pass data to function read_packet.
-/// @param read_packet Custom read function that is called from FFmpeg to
-/// read data from the destination.
-/// @param seek Optional seek function that is used to seek the destination.
-struct StreamReaderCustomIO : private detail::CustomInput, public StreamReader {
+/// A subclass of StreamReader which works with custom read function.
+/// Can be used for decoding media from memory or custom object.
+///
+class StreamReaderCustomIO : private detail::CustomInput, public StreamReader {
+ public:
+  ///
+  /// Construct StreamReader with custom read and seek functions.
+  ///
+  /// @param opaque Custom data used by ``read_packet`` and ``seek`` functions.
+  /// @param format Specify input format.
+  /// @param buffer_size The size of the intermediate buffer, which FFmpeg uses
+  /// to pass data to function read_packet.
+  /// @param read_packet Custom read function that is called from FFmpeg to
+  /// read data from the destination.
+  /// @param seek Optional seek function that is used to seek the destination.
+  /// @param option Custom option passed when initializing format context.
   StreamReaderCustomIO(
       void* opaque,
       const c10::optional<std::string>& format,

torchaudio/csrc/ffmpeg/stream_writer/stream_writer.h

@@ -306,17 +306,21 @@ struct CustomOutput {
 
 /// @endcond
 
-/// Construct StreamWriter with custom write and seek functions.
 ///
-/// @param opaque Custom data used by write_packet and seek functions.
-/// @param format Specify output format.
-/// @param buffer_size The size of the intermediate buffer, which FFmpeg uses to
-/// pass data to write_packet function.
-/// @param write_packet Custom write function that is called from FFmpeg to
-/// actually write data to the custom destination.
-/// @param seek Optional seek function that is used to seek the destination.
-struct StreamWriterCustomIO : private detail::CustomOutput,
-                              public StreamWriter {
+/// A subclass of StreamReader which works with custom read function.
+/// Can be used for encoding media into memory or custom object.
+///
+class StreamWriterCustomIO : private detail::CustomOutput, public StreamWriter {
+ public:
+  /// Construct StreamWriterCustomIO with custom write and seek functions.
+  ///
+  /// @param opaque Custom data used by ``write_packet`` and ``seek`` functions.
+  /// @param format Specify output format.
+  /// @param buffer_size The size of the intermediate buffer, which FFmpeg uses
+  /// to pass data to write_packet function.
+  /// @param write_packet Custom write function that is called from FFmpeg to
+  /// actually write data to the custom destination.
+  /// @param seek Optional seek function that is used to seek the destination.
   StreamWriterCustomIO(
       void* opaque,
       const c10::optional<std::string>& format,