Add StreamWriter tutorial (#2698)

Summary:
Add a tutorial for basic usage of torchaudio.io.StreamWriter.

https://output.circle-artifacts.com/output/job/55d9a495-af7a-483c-84cb-de9a08cfd2f3/artifacts/0/docs/tutorials/streamwriter_basic_tutorial.html

Pull Request resolved: https://github.com/pytorch/audio/pull/2698

Reviewed By: carolineechen

Differential Revision: D40133007

Pulled By: carolineechen

fbshipit-source-id: 141f692c32343981bfb228357f21562ffe36f623

docs/source/tutorials.io.rst

@@ -16,5 +16,6 @@ wide variety of media formats, including audio and video, coming from many diffe
    tutorials/audio_io_tutorial
    tutorials/streamreader_basic_tutorial
    tutorials/streamreader_advanced_tutorial
+   tutorials/streamwriter_basic_tutorial
    tutorials/streamwriter_advanced
    hw_acceleration_tutorial

torchaudio/csrc/ffmpeg/stream_writer/stream_writer.cpp

@@ -238,8 +238,7 @@ void open_codec(
   AVDictionary* opt = get_option_dict(option);
   int ret = avcodec_open2(codec_ctx, codec_ctx->codec, &opt);
   clean_up_dict(opt);
-  TORCH_CHECK(
-      ret >= 0, "Failed to open audio codec: (", av_err2string(ret), ")");
+  TORCH_CHECK(ret >= 0, "Failed to open codec: (", av_err2string(ret), ")");
 }
 
 AVFramePtr get_audio_frame(

torchaudio/io/_stream_writer.py

@@ -15,7 +15,7 @@ def _format_doc(**kwargs):
 _encoder = """The name of the encoder to be used.
                 When provided, use the specified encoder instead of the default one.
 
-                To list the available encoders, you can use ``ffmpeg -h encoders`` command.
+                To list the available encoders, you can use ``ffmpeg -encoders`` command.
 
                 Default: ``None``."""
 
@@ -256,22 +256,25 @@ class StreamWriter:
             self._is_open = False
 
     def write_audio_chunk(self, i: int, chunk: torch.Tensor):
-        """Write the audio data
+        """Write audio data
 
         Args:
             i (int): Stream index.
             chunk (Tensor): Waveform tensor. Shape: `(frame, channel)`.
-                The ``dtype`` must match what was passed to :py:func:`add_audio_stream` method.
+                The ``dtype`` must match what was passed to :py:meth:`add_audio_stream` method.
         """
         self._s.write_audio_chunk(i, chunk)
 
     def write_video_chunk(self, i: int, chunk: torch.Tensor):
-        """Write the audio data
+        """Write video/image data
 
         Args:
             i (int): Stream index.
-            chunk (Tensor): Waveform tensor. Shape: `(frame, channel, height, width)`.
-                ``dtype``: ``torch.uint8``.
+            chunk (Tensor): Video/image tensor.
+                Shape: `(time, channel, height, width)`.
+                The ``dtype`` must be ``torch.uint8``.
+                The shape (height, width and the number of channels) must match
+                what was configured when calling :py:meth:`add_video_stream`
         """
         self._s.write_video_chunk(i, chunk)