Add StreamWriter (#2628)

Summary:
This commit adds FFmpeg-based encoder StreamWriter class.
StreamWriter is pretty much the opposite of StreamReader class, and
it supports;

* Encoding audio / still image / video
* Exporting to local file / streaming protocol / devices etc...
* File-like object support (in later commit)
* HW video encoding (in later commit)

See also: https://fburl.com/gslide/z85kn5a9 (Meta internal)

Pull Request resolved: https://github.com/pytorch/audio/pull/2628

Reviewed By: nateanl

Differential Revision: D38816650

Pulled By: mthrok

fbshipit-source-id: a9343b0d55755e186971dc96fb86eb52daa003c8

.circleci/unittest/linux/scripts/install.sh

@@ -80,7 +80,7 @@ fi
 (
     set -x
     conda install -y -c conda-forge ${NUMBA_DEV_CHANNEL} 'librosa>=0.8.0' parameterized 'requests>=2.20'
-    pip install kaldi-io SoundFile coverage pytest pytest-cov 'scipy==1.7.3' transformers expecttest unidecode inflect Pillow sentencepiece pytorch-lightning 'protobuf<4.21.0' demucs
+    pip install kaldi-io SoundFile coverage pytest pytest-cov 'scipy==1.7.3' transformers expecttest unidecode inflect Pillow sentencepiece pytorch-lightning 'protobuf<4.21.0' demucs tinytag
 )
 # Install fairseq
 git clone https://github.com/pytorch/fairseq

.circleci/unittest/windows/scripts/install.sh

@@ -88,7 +88,8 @@ esac
         transformers \
         unidecode \
         'protobuf<4.21.0' \
-        demucs
+        demucs \
+        tinytag
 )
 # Install fairseq
 git clone https://github.com/pytorch/fairseq

docs/source/io.rst

@@ -33,3 +33,10 @@ StreamReaderOutputStream
 
 .. autoclass:: StreamReaderOutputStream
   :members:
+
+
+StreamWriter
+------------
+
+.. autoclass:: StreamWriter
+  :members:

test/torchaudio_unittest/io/stream_writer_test.py

+import torch
+import torchaudio
+
+from parameterized import parameterized
+from torchaudio_unittest.common_utils import (
+    get_asset_path,
+    is_ffmpeg_available,
+    nested_params,
+    rgb_to_yuv_ccir,
+    skipIfNoFFmpeg,
+    skipIfNoModule,
+    TempDirMixin,
+    TorchaudioTestCase,
+)
+
+if is_ffmpeg_available():
+    from torchaudio.io import StreamReader, StreamWriter
+
+
+# TODO:
+# Get rid of StreamReader and use synthetic data.
+
+
+def get_audio_chunk(fmt, sample_rate, num_channels):
+    path = get_asset_path("nasa_13013.mp4")
+    s = StreamReader(path)
+    for _ in range(num_channels):
+        s.add_basic_audio_stream(-1, -1, format=fmt, sample_rate=sample_rate)
+    s.stream()
+    s.process_all_packets()
+    chunks = [chunk[:, :1] for chunk in s.pop_chunks()]
+    return torch.cat(chunks, 1)
+
+
+def get_video_chunk(fmt, frame_rate, *, width, height):
+    path = get_asset_path("nasa_13013_no_audio.mp4")
+    s = StreamReader(path)
+    s.add_basic_video_stream(-1, -1, format=fmt, frame_rate=frame_rate, width=width, height=height)
+    s.stream()
+    s.process_all_packets()
+    (chunk,) = s.pop_chunks()
+    return chunk
+
+
+@skipIfNoFFmpeg
+class StreamWriterInterfaceTest(TempDirMixin, TorchaudioTestCase):
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+        torchaudio.utils.ffmpeg_utils.set_log_level(32)
+
+    @classmethod
+    def tearDownClass(cls):
+        torchaudio.utils.ffmpeg_utils.set_log_level(8)
+        super().tearDownClass()
+
+    def get_dst(self, path):
+        return self.get_temp_path(path)
+
+    def get_buf(self, path):
+        with open(self.get_temp_path(path), "rb") as fileobj:
+            return fileobj.read()
+
+    @skipIfNoModule("tinytag")
+    def test_metadata_overwrite(self):
+        """When set_metadata is called multiple times, only entries from the last call are saved"""
+        from tinytag import TinyTag
+
+        src_fmt = "s16"
+        sample_rate = 8000
+        num_channels = 1
+
+        path = self.get_dst("test.mp3")
+        s = StreamWriter(path, format="mp3")
+        s.set_metadata(metadata={"artist": "torchaudio", "title": "foo"})
+        s.set_metadata(metadata={"title": self.id()})
+        s.add_audio_stream(sample_rate, num_channels, format=src_fmt)
+
+        chunk = get_audio_chunk(src_fmt, sample_rate, num_channels)
+        with s.open():
+            s.write_audio_chunk(0, chunk)
+
+        tag = TinyTag.get(path)
+        assert tag.artist is None
+        assert tag.title == self.id()
+
+    @nested_params(
+        # Note: "s64" causes UB (left shift of 1 by 63 places cannot be represented in type 'long')
+        # thus it's omitted.
+        ["u8", "s16", "s32", "flt", "dbl"],
+        [8000, 16000, 44100],
+        [1, 2, 4],
+    )
+    def test_valid_audio_muxer_and_codecs_wav(self, src_fmt, sample_rate, num_channels):
+        """Tensor of various dtypes can be saved as wav format."""
+        path = self.get_dst("test.wav")
+        s = StreamWriter(path, format="wav")
+        s.set_metadata(metadata={"artist": "torchaudio", "title": self.id()})
+        s.add_audio_stream(sample_rate, num_channels, format=src_fmt)
+
+        chunk = get_audio_chunk(src_fmt, sample_rate, num_channels)
+        with s.open():
+            s.write_audio_chunk(0, chunk)
+
+    @parameterized.expand(
+        [
+            ("mp3", 8000, 1, "s32p", None),
+            ("mp3", 16000, 2, "fltp", None),
+            ("mp3", 44100, 1, "s16p", {"abr": "true"}),
+            ("flac", 8000, 1, "s16", None),
+            ("flac", 16000, 2, "s32", None),
+            ("opus", 48000, 2, None, {"strict": "experimental"}),
+            ("adts", 8000, 1, "fltp", None),  # AAC format
+        ]
+    )
+    def test_valid_audio_muxer_and_codecs(self, ext, sample_rate, num_channels, encoder_format, encoder_option):
+        """Tensor of various dtypes can be saved as given format."""
+        path = self.get_dst(f"test.{ext}")
+        s = StreamWriter(path, format=ext)
+        s.set_metadata(metadata={"artist": "torchaudio", "title": self.id()})
+        s.add_audio_stream(sample_rate, num_channels, encoder_option=encoder_option, encoder_format=encoder_format)
+
+        chunk = get_audio_chunk("flt", sample_rate, num_channels)
+        with s.open():
+            s.write_audio_chunk(0, chunk)
+
+    @nested_params(
+        [
+            "gray8",
+            "rgb24",
+            "bgr24",
+            "yuv444p",
+        ],
+        [(128, 64), (720, 576)],
+    )
+    def test_valid_video_muxer_and_codecs(self, src_format, size):
+        """Image tensors of various formats can be saved as mp4"""
+        ext = "mp4"
+        frame_rate = 10
+        width, height = size
+
+        path = self.get_dst(f"test.{ext}")
+        s = StreamWriter(path, format=ext)
+        s.add_video_stream(frame_rate, width, height, format=src_format)
+
+        chunk = get_video_chunk(src_format, frame_rate, width=width, height=height)
+        with s.open():
+            s.write_video_chunk(0, chunk)
+
+    def test_valid_audio_video_muxer(self):
+        """Audio/image tensors are saved as single video"""
+        ext = "mp4"
+
+        sample_rate = 16000
+        num_channels = 3
+
+        frame_rate = 30000 / 1001
+        width, height = 720, 576
+        video_fmt = "yuv444p"
+
+        path = self.get_dst(f"test.{ext}")
+        s = StreamWriter(path, format=ext)
+        s.set_metadata({"artist": "torchaudio", "title": self.id()})
+        s.add_audio_stream(sample_rate, num_channels)
+        s.add_video_stream(frame_rate, width, height, format=video_fmt)
+
+        audio = get_audio_chunk("flt", sample_rate, num_channels)
+        video = get_video_chunk(video_fmt, frame_rate, height=height, width=width)
+
+        with s.open():
+            s.write_audio_chunk(0, audio)
+            s.write_video_chunk(1, video)
+
+    @nested_params(
+        [
+            ("gray8", "gray8"),
+            ("rgb24", "rgb24"),
+            ("bgr24", "bgr24"),
+            ("yuv444p", "yuv444p"),
+            ("rgb24", "yuv444p"),
+            ("bgr24", "yuv444p"),
+        ],
+    )
+    def test_video_raw_out(self, formats):
+        """Verify that viedo out is correct with/without color space conversion"""
+        filename = "test.rawvideo"
+        frame_rate = 30000 / 1001
+
+        width, height = 720, 576
+        src_fmt, encoder_fmt = formats
+        frames = int(frame_rate * 2)
+        channels = 1 if src_fmt == "gray8" else 3
+
+        # Generate data
+        src_size = (frames, channels, height, width)
+        chunk = torch.randint(low=0, high=255, size=src_size, dtype=torch.uint8)
+
+        # Write data
+        dst = self.get_dst(filename)
+        s = StreamWriter(dst, format="rawvideo")
+        s.add_video_stream(frame_rate, width, height, format=src_fmt, encoder_format=encoder_fmt)
+        with s.open():
+            s.write_video_chunk(0, chunk)
+
+        # Fetch the written data
+        buf = self.get_buf(filename)
+        result = torch.frombuffer(buf, dtype=torch.uint8)
+        if encoder_fmt.endswith("p"):
+            result = result.reshape(src_size)
+        else:
+            result = result.reshape(frames, height, width, channels).permute(0, 3, 1, 2)
+
+        # check that they are same
+        if src_fmt == encoder_fmt:
+            expected = chunk
+        else:
+            if src_fmt == "bgr24":
+                chunk = chunk[:, [2, 1, 0], :, :]
+            expected = rgb_to_yuv_ccir(chunk)
+        self.assertEqual(expected, result, atol=1, rtol=0)

torchaudio/csrc/CMakeLists.txt

@@ -149,6 +149,9 @@ if(USE_FFMPEG)
     ffmpeg/stream_reader/stream_reader.cpp
     ffmpeg/stream_reader/stream_reader_wrapper.cpp
     ffmpeg/stream_reader/stream_reader_binding.cpp
+    ffmpeg/stream_writer/stream_writer.cpp
+    ffmpeg/stream_writer/stream_writer_wrapper.cpp
+    ffmpeg/stream_writer/stream_writer_binding.cpp
     ffmpeg/utils.cpp
     )
   message(STATUS "FFMPEG_ROOT=$ENV{FFMPEG_ROOT}")

torchaudio/csrc/ffmpeg/ffmpeg.cpp

@@ -47,10 +47,18 @@ void AVFormatInputContextDeleter::operator()(AVFormatContext* p) {
 AVFormatInputContextPtr::AVFormatInputContextPtr(AVFormatContext* p)
     : Wrapper<AVFormatContext, AVFormatInputContextDeleter>(p) {}
 
+void AVFormatOutputContextDeleter::operator()(AVFormatContext* p) {
+  avformat_free_context(p);
+};
+
+AVFormatOutputContextPtr::AVFormatOutputContextPtr(AVFormatContext* p)
+    : Wrapper<AVFormatContext, AVFormatOutputContextDeleter>(p) {}
+
 ////////////////////////////////////////////////////////////////////////////////
 // AVIO
 ////////////////////////////////////////////////////////////////////////////////
 void AVIOContextDeleter::operator()(AVIOContext* p) {
+  avio_flush(p);
   av_freep(&p->buffer);
   av_freep(&p);
 };

torchaudio/csrc/ffmpeg/ffmpeg.h

@@ -93,6 +93,15 @@ struct AVFormatInputContextPtr
   explicit AVFormatInputContextPtr(AVFormatContext* p);
 };
 
+struct AVFormatOutputContextDeleter {
+  void operator()(AVFormatContext* p);
+};
+
+struct AVFormatOutputContextPtr
+    : public Wrapper<AVFormatContext, AVFormatOutputContextDeleter> {
+  explicit AVFormatOutputContextPtr(AVFormatContext* p);
+};
+
 ////////////////////////////////////////////////////////////////////////////////
 // AVIO
 ////////////////////////////////////////////////////////////////////////////////

torchaudio/csrc/ffmpeg/stream_writer/stream_writer.h

+#pragma once
+
+#include <torch/torch.h>
+#include <torchaudio/csrc/ffmpeg/ffmpeg.h>
+#include <torchaudio/csrc/ffmpeg/filter_graph.h>
+
+namespace torchaudio {
+namespace ffmpeg {
+
+struct OutputStream {
+  AVStream* stream;
+  AVCodecContextPtr codec_ctx;
+  std::unique_ptr<FilterGraph> filter;
+  AVFramePtr src_frame;
+  AVFramePtr dst_frame;
+  // The number of samples written so far
+  int64_t num_frames;
+  // Audio-only: The maximum frames that frame can hold
+  int64_t frame_capacity;
+};
+
+class StreamWriter {
+  AVFormatOutputContextPtr pFormatContext;
+  std::vector<OutputStream> streams;
+  AVPacketPtr pkt;
+
+ public:
+  explicit StreamWriter(AVFormatOutputContextPtr&& p);
+  // Non-copyable
+  StreamWriter(const StreamWriter&) = delete;
+  StreamWriter& operator=(const StreamWriter&) = delete;
+
+  //////////////////////////////////////////////////////////////////////////////
+  // Query methods
+  //////////////////////////////////////////////////////////////////////////////
+ public:
+  // Print the configured outputs
+  void dump_format(int64_t i);
+
+  //////////////////////////////////////////////////////////////////////////////
+  // Configure methods
+  //////////////////////////////////////////////////////////////////////////////
+ public:
+  void add_audio_stream(
+      int64_t sample_rate,
+      int64_t num_channels,
+      const std::string& format,
+      const c10::optional<std::string>& encoder,
+      const c10::optional<OptionDict>& encoder_option,
+      const c10::optional<std::string>& encoder_format);
+  void add_video_stream(
+      double frame_rate,
+      int64_t width,
+      int64_t height,
+      const std::string& format,
+      const c10::optional<std::string>& encoder,
+      const c10::optional<OptionDict>& encoder_option,
+      const c10::optional<std::string>& encoder_format);
+  void set_metadata(const OptionDict& metadata);
+
+ private:
+  AVStream* add_stream(AVCodecContextPtr& ctx);
+
+  //////////////////////////////////////////////////////////////////////////////
+  // Write methods
+  //////////////////////////////////////////////////////////////////////////////
+ public:
+  void open(const c10::optional<OptionDict>& opt);
+  void close();
+
+  void write_audio_chunk(int i, const torch::Tensor& chunk);
+  void write_video_chunk(int i, const torch::Tensor& chunk);
+  void flush();
+
+ private:
+  void validate_stream(int i, enum AVMediaType);
+  void write_planar_video(
+      OutputStream& os,
+      const torch::Tensor& chunk,
+      int num_planes);
+  void write_interlaced_video(OutputStream& os, const torch::Tensor& chunk);
+  void process_frame(
+      AVFrame* src_frame,
+      std::unique_ptr<FilterGraph>& filter,
+      AVFrame* dst_frame,
+      AVCodecContextPtr& c,
+      AVStream* st);
+  void encode_frame(AVFrame* dst_frame, AVCodecContextPtr& c, AVStream* st);
+  void flush_stream(OutputStream& os);
+};
+
+} // namespace ffmpeg
+} // namespace torchaudio

torchaudio/csrc/ffmpeg/stream_writer/stream_writer_binding.cpp

+#include <torch/script.h>
+#include <torchaudio/csrc/ffmpeg/stream_writer/stream_writer_wrapper.h>
+
+namespace torchaudio {
+namespace ffmpeg {
+namespace {
+
+c10::intrusive_ptr<StreamWriterBinding> init(
+    const std::string& dst,
+    const c10::optional<std::string>& format) {
+  return c10::make_intrusive<StreamWriterBinding>(
+      get_output_format_context(dst, format));
+}
+
+using S = const c10::intrusive_ptr<StreamWriterBinding>&;
+
+TORCH_LIBRARY_FRAGMENT(torchaudio, m) {
+  m.class_<StreamWriterBinding>("ffmpeg_StreamWriter")
+      .def(torch::init<>(init))
+      .def(
+          "add_audio_stream",
+          [](S s,
+             int64_t sample_rate,
+             int64_t num_channels,
+             const std::string& format,
+             const c10::optional<std::string>& encoder,
+             const c10::optional<OptionDict>& encoder_option,
+             const c10::optional<std::string>& encoder_format) {
+            s->add_audio_stream(
+                sample_rate,
+                num_channels,
+                format,
+                encoder,
+                encoder_option,
+                encoder_format);
+          })
+      .def(
+          "add_video_stream",
+          [](S s,
+             double frame_rate,
+             int64_t width,
+             int64_t height,
+             const std::string& format,
+             const c10::optional<std::string>& encoder,
+             const c10::optional<OptionDict>& encoder_option,
+             const c10::optional<std::string>& encoder_format) {
+            s->add_video_stream(
+                frame_rate,
+                width,
+                height,
+                format,
+                encoder,
+                encoder_option,
+                encoder_format);
+          })
+      .def(
+          "set_metadata",
+          [](S s, const OptionDict& metadata) { s->set_metadata(metadata); })
+      .def("dump_format", [](S s, int64_t i) { s->dump_format(i); })
+      .def(
+          "open",
+          [](S s, const c10::optional<OptionDict>& option) { s->open(option); })
+      .def("close", [](S s) { s->close(); })
+      .def(
+          "write_audio_chunk",
+          [](S s, int64_t i, const torch::Tensor& chunk) {
+            s->write_audio_chunk(static_cast<int>(i), chunk);
+          })
+      .def(
+          "write_video_chunk",
+          [](S s, int64_t i, const torch::Tensor& chunk) {
+            s->write_video_chunk(static_cast<int>(i), chunk);
+          })
+      .def("flush", [](S s) { s->flush(); });
+}
+
+} // namespace
+} // namespace ffmpeg
+} // namespace torchaudio

torchaudio/csrc/ffmpeg/stream_writer/stream_writer_wrapper.cpp

+#include <torchaudio/csrc/ffmpeg/stream_writer/stream_writer_wrapper.h>
+
+namespace torchaudio {
+namespace ffmpeg {
+
+AVFormatOutputContextPtr get_output_format_context(
+    const std::string& dst,
+    const c10::optional<std::string>& format) {
+  AVFormatContext* p = avformat_alloc_context();
+  TORCH_CHECK(p, "Failed to allocate AVFormatContext.");
+
+  int ret = avformat_alloc_output_context2(
+      &p, nullptr, format ? format.value().c_str() : nullptr, dst.c_str());
+  TORCH_CHECK(
+      ret >= 0,
+      "Failed to open output \"",
+      dst,
+      "\" (",
+      av_err2string(ret),
+      ").");
+
+  return AVFormatOutputContextPtr(p);
+}
+
+StreamWriterBinding::StreamWriterBinding(AVFormatOutputContextPtr&& p)
+    : StreamWriter(std::move(p)) {}
+
+} // namespace ffmpeg
+} // namespace torchaudio

torchaudio/csrc/ffmpeg/stream_writer/stream_writer_wrapper.h

+#pragma once
+#include <torchaudio/csrc/ffmpeg/stream_writer/stream_writer.h>
+
+namespace torchaudio {
+namespace ffmpeg {
+
+// create format context for writing media
+AVFormatOutputContextPtr get_output_format_context(
+    const std::string& dst,
+    const c10::optional<std::string>& format);
+
+class StreamWriterBinding : public StreamWriter,
+                            public torch::CustomClassHolder {
+ public:
+  explicit StreamWriterBinding(AVFormatOutputContextPtr&& p);
+};
+
+} // namespace ffmpeg
+} // namespace torchaudio

torchaudio/io/__init__.py

 import torchaudio
 
-_LAZILY_IMPORTED = [
+_STREAM_READER = [
     "StreamReader",
     "StreamReaderSourceStream",
     "StreamReaderSourceAudioStream",
@@ -8,15 +8,28 @@ _LAZILY_IMPORTED = [
     "StreamReaderOutputStream",
 ]
 
+_STREAM_WRITER = [
+    "StreamWriter",
+]
+
+
+_LAZILY_IMPORTED = _STREAM_READER + _STREAM_WRITER
+
 
 def __getattr__(name: str):
     if name in _LAZILY_IMPORTED:
-
         torchaudio._extension._init_ffmpeg()
 
+        if name in _STREAM_READER:
             from . import _stream_reader
 
             item = getattr(_stream_reader, name)
+
+        else:
+            from . import _stream_writer
+
+            item = getattr(_stream_writer, name)
+
         globals()[name] = item
         return item
     raise AttributeError(f"module {__name__} has no attribute {name}")

torchaudio/io/_stream_writer.py

+from typing import Dict, Optional
+
+import torch
+
+
+def _format_doc(**kwargs):
+    def decorator(obj):
+        obj.__doc__ = obj.__doc__.format(**kwargs)
+        return obj
+
+    return decorator
+
+
+_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.
+
+                Default: ``None``."""
+
+
+_encoder_option = """Options passed to encoder.
+                Mapping from str to str.
+
+                To list encoder options for a encoder, you can use
+                ``ffmpeg -h encoder=<ENCODER>`` command.
+
+                Default: ``None``."""
+
+
+_encoder_format = """Format used to encode media.
+                When encoder supports multiple formats, passing this argument will override
+                the format used for encoding.
+
+                To list supported formats for the encoder, you can use
+                ``ffmpeg -h encoder=<ENCODER>`` command.
+
+                Default: ``None``."""
+
+
+_format_common_args = _format_doc(
+    encoder=_encoder,
+    encoder_option=_encoder_option,
+    encoder_format=_encoder_format,
+)
+
+
+class StreamWriter:
+    """Encode and write audio/video streams chunk by chunk
+
+    Args:
+        dst (str): The destination where the encoded data are written.
+            The supported value depends on the FFmpeg found in the system.
+
+        format (str or None, optional):
+            Override the output format, or specify the output media device.
+            Default: ``None`` (no override nor device output).
+
+            This argument serves two different use cases.
+
+            1) Override the output format.
+               This is useful when writing raw data or in a format different from the extension.
+
+            2) Specify the output device.
+               This allows to output media streams to hardware devices,
+               such as speaker and video screen.
+
+            .. note::
+
+               This option roughly corresponds to ``-f`` option of ``ffmpeg`` command.
+               Please refer to the ffmpeg documentations for possible values.
+
+               https://ffmpeg.org/ffmpeg-formats.html#Muxers
+
+               Use `ffmpeg -muxers` to list the values available in the current environment.
+
+               For device access, the available values vary based on hardware (AV device) and
+               software configuration (ffmpeg build).
+               Please refer to the ffmpeg documentations for possible values.
+
+               https://ffmpeg.org/ffmpeg-devices.html#Output-Devices
+
+               Use `ffmpeg -devices` to list the values available in the current environment.
+    """
+
+    def __init__(
+        self,
+        dst: str,
+        format: Optional[str] = None,
+    ):
+        self._s = torch.classes.torchaudio.ffmpeg_StreamWriter(dst, format)
+        self._is_open = False
+
+    @_format_common_args
+    def add_audio_stream(
+        self,
+        sample_rate: int,
+        num_channels: int,
+        format: str = "flt",
+        encoder: Optional[str] = None,
+        encoder_option: Optional[Dict[str, str]] = None,
+        encoder_format: Optional[str] = None,
+    ):
+        """Add an output audio stream.
+
+        Args:
+            sample_rate (int): The sample rate.
+
+            num_channels (int): The number of channels.
+
+            format (str, optional): Input sample format, which determines the dtype
+                of the input tensor.
+
+                - ``"u8"``: The input tensor must be ``torch.uint8`` type.
+                - ``"s16"``: The input tensor must be ``torch.int16`` type.
+                - ``"s32"``: The input tensor must be ``torch.int32`` type.
+                - ``"s64"``: The input tensor must be ``torch.int64`` type.
+                - ``"flt"``: The input tensor must be ``torch.float32`` type.
+                - ``"dbl"``: The input tensor must be ``torch.float64`` type.
+
+                Default: ``"flt"``.
+
+            encoder (str or None, optional): {encoder}
+
+            encoder_option (dict or None, optional): {encoder_option}
+
+            encoder_format (str or None, optional): {encoder_format}
+        """
+        self._s.add_audio_stream(sample_rate, num_channels, format, encoder, encoder_option, encoder_format)
+
+    @_format_common_args
+    def add_video_stream(
+        self,
+        frame_rate: float,
+        width: int,
+        height: int,
+        format: str = "rgb24",
+        encoder: Optional[str] = None,
+        encoder_option: Optional[Dict[str, str]] = None,
+        encoder_format: Optional[str] = None,
+    ):
+        """Add an output video stream.
+
+        This method has to be called before `open` is called.
+
+        Args:
+            frame_rate (float): Frame rate of the video.
+
+            width (int): Width of the video frame.
+
+            height (int): Height of the video frame.
+
+            format (str, optional): Input pixel format, which determines the
+                color channel order of the input tensor.
+
+                - ``"gray8"``: One channel, grayscale.
+                - ``"rgb24"``: Three channels in the order of RGB.
+                - ``"bgr24"``: Three channels in the order of BGR.
+                - ``"yuv444p"``: Three channels in the order of YUV.
+
+                Default: ``"rgb24"``.
+
+                In either case, the input tensor has to be ``torch.uint8`` type and
+                the shape must be (frame, channel, height, width).
+
+            encoder (str or None, optional): {encoder}
+
+            encoder_option (dict or None, optional): {encoder_option}
+
+            encoder_format (str or None, optional): {encoder_format}
+        """
+        self._s.add_video_stream(frame_rate, width, height, format, encoder, encoder_option, encoder_format)
+
+    def set_metadata(self, metadata: Dict[str, str]):
+        """Set file-level metadata
+
+        Args:
+            metadata (dict or None, optional): File-level metadata.
+        """
+        self._s.set_metadata(metadata)
+
+    def _print_output_stream(self, i: int):
+        """[debug] Print the registered stream information to stdout."""
+        self._s.dump_format(i)
+
+    def open(self, option: Optional[Dict[str, str]] = None):
+        """Open the output file / device and write the header.
+
+        Args:
+            option (dict or None, optional): Private options for protocol, device and muxer. See example.
+
+        Example - Protocol option
+            >>> s = StreamWriter(dst="rtmp://localhost:1234/live/app", format="flv")
+            >>> s.add_video_stream(...)
+            >>> # Passing protocol option `listen=1` makes StreamWriter act as RTMP server.
+            >>> with s.open(option={"listen": "1"}) as f:
+            >>>     f.write_video_chunk(...)
+
+        Example - Device option
+            >>> s = StreamWriter("-", format="sdl")
+            >>> s.add_video_stream(..., encoder_format="rgb24")
+            >>> # Open SDL video player with fullscreen
+            >>> with s.open(option={"window_fullscreen": "1"}):
+            >>>     f.write_video_chunk(...)
+
+        Example - Muxer option
+            >>> s = StreamWriter("foo.flac")
+            >>> s.add_audio_stream(...)
+            >>> s.set_metadata({"artist": "torchaudio contributors"})
+            >>> # FLAC muxer has a private option to not write the header.
+            >>> # The resulting file does not contain the above metadata.
+            >>> with s.open(option={"write_header": "false"}) as f:
+            >>>     f.write_audio_chunk(...)
+        """
+        if not self._is_open:
+            self._s.open(option)
+            self._is_open = True
+        return self
+
+    def close(self):
+        """Close the output"""
+        if self._is_open:
+            self._s.close()
+            self._is_open = False
+
+    def write_audio_chunk(self, i: int, chunk: torch.Tensor):
+        """Write the 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.
+        """
+        self._s.write_audio_chunk(i, chunk)
+
+    def write_video_chunk(self, i: int, chunk: torch.Tensor):
+        """Write the audio data
+
+        Args:
+            i (int): Stream index.
+            chunk (Tensor): Waveform tensor. Shape: `(frame, channel, height, width)`.
+                ``dtype``: ``torch.uint8``.
+        """
+        self._s.write_video_chunk(i, chunk)
+
+    def flush(self):
+        """Flush the frames from encoders and write the frames to the destination."""
+        self._s.flush()
+
+    def __enter__(self):
+        """Context manager so that the destination is closed and data are flushed automatically."""
+        return self
+
+    def __exit__(self, exception_type, exception_value, traceback):
+        """Context manager so that the destination is closed and data are flushed automatically."""
+        self.flush()
+        self.close()