Include format information after filter (#3155)

Summary:
This commit adds fields to OutputStream, which shows the result
of fitlers, such as width and height after filtering.

Before

```
OutputStream(
    source_index=0,
    filter_description='fps=3,scale=width=320:height=320,format=pix_fmts=gray')
```

After

```
OutputVideoStream(
    source_index=0,
    filter_description='fps=3,scale=width=320:height=320,format=pix_fmts=gray',
    media_type='video',
    format='gray',
    width=320,
    height=320,
    frame_rate=3.0)
```

Pull Request resolved: https://github.com/pytorch/audio/pull/3155

Reviewed By: nateanl

Differential Revision: D43882399

Pulled By: mthrok

fbshipit-source-id: 620676b1a06f293fdd56de8203a11120f228fa2d

docs/source/_templates/autosummary/io_class.rst

@@ -61,6 +61,8 @@ Support Structures
     "SourceAudioStream",
     "SourceVideoStream",
     "OutputStream",
+    "OutputAudioStream",
+    "OutputVideoStream",
 ] %}
 
 {{ item | underline("~") }}

test/torchaudio_unittest/io/stream_reader_test.py

@@ -20,7 +20,14 @@ from torchaudio_unittest.common_utils import (
 
 if is_ffmpeg_available():
     from torchaudio.io import StreamReader, StreamWriter
-    from torchaudio.io._stream_reader import ChunkTensor, SourceAudioStream, SourceStream, SourceVideoStream
+    from torchaudio.io._stream_reader import (
+        ChunkTensor,
+        OutputAudioStream,
+        OutputVideoStream,
+        SourceAudioStream,
+        SourceStream,
+        SourceVideoStream,
+    )
 
 
 @skipIfNoFFmpeg
@@ -238,6 +245,81 @@ class StreamReaderInterfaceTest(_MediaSourceMixin, TempDirMixin, TorchaudioTestC
         output = [s.get_src_stream_info(i) for i in range(6)]
         assert expected == output
 
+    def test_output_info(self):
+        s = StreamReader(self.get_src())
+
+        s.add_audio_stream(-1)
+        s.add_audio_stream(-1, filter_desc="aresample=8000")
+        s.add_audio_stream(-1, filter_desc="aformat=sample_fmts=s16p")
+        s.add_video_stream(-1)
+        s.add_video_stream(-1, filter_desc="fps=10")
+        s.add_video_stream(-1, filter_desc="format=rgb24")
+        s.add_video_stream(-1, filter_desc="scale=w=160:h=90")
+        expected = [
+            OutputAudioStream(
+                source_index=4,
+                filter_description="anull",
+                media_type="audio",
+                format="fltp",
+                sample_rate=16000.0,
+                num_channels=2,
+            ),
+            OutputAudioStream(
+                source_index=4,
+                filter_description="aresample=8000",
+                media_type="audio",
+                format="fltp",
+                sample_rate=8000.0,
+                num_channels=2,
+            ),
+            OutputAudioStream(
+                source_index=4,
+                filter_description="aformat=sample_fmts=s16p",
+                media_type="audio",
+                format="s16p",
+                sample_rate=16000.0,
+                num_channels=2,
+            ),
+            OutputVideoStream(
+                source_index=3,
+                filter_description="null",
+                media_type="video",
+                format="yuv420p",
+                width=480,
+                height=270,
+                frame_rate=30000 / 1001,
+            ),
+            OutputVideoStream(
+                source_index=3,
+                filter_description="fps=10",
+                media_type="video",
+                format="yuv420p",
+                width=480,
+                height=270,
+                frame_rate=10,
+            ),
+            OutputVideoStream(
+                source_index=3,
+                filter_description="format=rgb24",
+                media_type="video",
+                format="rgb24",
+                width=480,
+                height=270,
+                frame_rate=30000 / 1001,
+            ),
+            OutputVideoStream(
+                source_index=3,
+                filter_description="scale=w=160:h=90",
+                media_type="video",
+                format="yuv420p",
+                width=160,
+                height=90,
+                frame_rate=30000 / 1001,
+            ),
+        ]
+        output = [s.get_out_stream_info(i) for i in range(s.num_out_streams)]
+        assert expected == output
+
     def test_id3tag(self):
         """get_metadata method can fetch id3tag properly"""
         s = StreamReader(self.get_src("steam-train-whistle-daniel_simon.mp3"))

torchaudio/csrc/ffmpeg/filter_graph.cpp

@@ -41,6 +41,7 @@ std::string get_audio_src_args(
 std::string get_video_src_args(
     AVPixelFormat format,
     AVRational time_base,
+    AVRational frame_rate,
     int width,
     int height,
     AVRational sample_aspect_ratio) {
@@ -48,12 +49,14 @@ std::string get_video_src_args(
   std::snprintf(
       args,
       sizeof(args),
-      "video_size=%dx%d:pix_fmt=%s:time_base=%d/%d:pixel_aspect=%d/%d",
+      "video_size=%dx%d:pix_fmt=%s:time_base=%d/%d:frame_rate=%d/%d:pixel_aspect=%d/%d",
       width,
       height,
       av_get_pix_fmt_name(format),
       time_base.num,
       time_base.den,
+      frame_rate.num,
+      frame_rate.den,
       sample_aspect_ratio.num,
       sample_aspect_ratio.den);
   return std::string(args);
@@ -76,13 +79,14 @@ void FilterGraph::add_audio_src(
 void FilterGraph::add_video_src(
     AVPixelFormat format,
     AVRational time_base,
+    AVRational frame_rate,
     int width,
     int height,
     AVRational sample_aspect_ratio) {
   TORCH_CHECK(
       media_type == AVMEDIA_TYPE_VIDEO, "The filter graph is not video type.");
-  std::string args =
-      get_video_src_args(format, time_base, width, height, sample_aspect_ratio);
+  std::string args = get_video_src_args(
+      format, time_base, frame_rate, width, height, sample_aspect_ratio);
   add_src(args);
 }
 
@@ -164,7 +168,7 @@ void FilterGraph::add_process(const std::string& filter_description) {
 void FilterGraph::create_filter() {
   int ret = avfilter_graph_config(pFilterGraph, nullptr);
   TORCH_CHECK(ret >= 0, "Failed to configure the graph: " + av_err2string(ret));
-  // char* desc = avfilter_graph_dump(pFilterGraph.get(), NULL);
+  // char* desc = avfilter_graph_dump(pFilterGraph, NULL);
   // std::cerr << "Filter created:\n" << desc << std::endl;
   // av_free(static_cast<void*>(desc));
 }
@@ -177,22 +181,26 @@ AVRational FilterGraph::get_output_timebase() const {
   return buffersink_ctx->inputs[0]->time_base;
 }
 
-int FilterGraph::get_output_sample_rate() const {
+FilterGraphOutputInfo FilterGraph::get_output_info() const {
   TORCH_INTERNAL_ASSERT(buffersink_ctx, "FilterGraph is not initialized.");
-  return buffersink_ctx->inputs[0]->sample_rate;
-}
-
-int FilterGraph::get_output_channels() const {
-  TORCH_INTERNAL_ASSERT(buffersink_ctx, "FilterGraph is not initialized.");
-  // Since FFmpeg 5.1
-  // https://github.com/FFmpeg/FFmpeg/blob/release/5.1/doc/APIchanges#L45-L54
+  AVFilterLink* l = buffersink_ctx->inputs[0];
+  FilterGraphOutputInfo ret{};
+  ret.type = l->type;
+  ret.format = l->format;
+  if (l->type == AVMEDIA_TYPE_AUDIO) {
+    ret.sample_rate = l->sample_rate;
 #if LIBAVFILTER_VERSION_MAJOR >= 8 && LIBAVFILTER_VERSION_MINOR >= 44
-  return buffersink_ctx->inputs[0]->ch_layout.nb_channels;
+    ret.num_channels = l->ch_layout.nb_channels;
 #else
     // Before FFmpeg 5.1
-  return av_get_channel_layout_nb_channels(
-      buffersink_ctx->inputs[0]->channel_layout);
+    ret.num_channels = av_get_channel_layout_nb_channels(l->channel_layout);
 #endif
+  } else {
+    ret.frame_rate = l->frame_rate;
+    ret.height = l->h;
+    ret.width = l->w;
+  }
+  return ret;
 }
 
 ////////////////////////////////////////////////////////////////////////////////

torchaudio/csrc/ffmpeg/filter_graph.h

@@ -4,6 +4,21 @@
 namespace torchaudio {
 namespace io {
 
+/// Used to report the output formats of filter graph.
+struct FilterGraphOutputInfo {
+  AVMediaType type = AVMEDIA_TYPE_UNKNOWN;
+  int format = -1;
+
+  // Audio
+  int sample_rate = -1;
+  int num_channels = -1;
+
+  // Video
+  AVRational frame_rate = {0, 1};
+  int height = -1;
+  int width = -1;
+};
+
 class FilterGraph {
   AVMediaType media_type;
 
@@ -37,6 +52,7 @@ class FilterGraph {
   void add_video_src(
       AVPixelFormat format,
       AVRational time_base,
+      AVRational frame_rate,
       int width,
       int height,
       AVRational sample_aspect_ratio);
@@ -53,8 +69,7 @@ class FilterGraph {
   // Query methods
   //////////////////////////////////////////////////////////////////////////////
   [[nodiscard]] AVRational get_output_timebase() const;
-  [[nodiscard]] int get_output_sample_rate() const;
-  [[nodiscard]] int get_output_channels() const;
+  [[nodiscard]] FilterGraphOutputInfo get_output_info() const;
 
   //////////////////////////////////////////////////////////////////////////////
   // Streaming process

torchaudio/csrc/ffmpeg/pybind/pybind.cpp

@@ -57,8 +57,44 @@ PYBIND11_MODULE(_torchaudio_ffmpeg, m) {
       .def("close", &StreamWriterFileObj::close);
   py::class_<OutputStreamInfo>(m, "OutputStreamInfo", py::module_local())
       .def_readonly("source_index", &OutputStreamInfo::source_index)
-      .def_readonly(
-          "filter_description", &OutputStreamInfo::filter_description);
+      .def_readonly("filter_description", &OutputStreamInfo::filter_description)
+      .def_property_readonly(
+          "media_type",
+          [](const OutputStreamInfo& o) -> std::string {
+            return av_get_media_type_string(o.media_type);
+          })
+      .def_property_readonly(
+          "format",
+          [](const OutputStreamInfo& o) -> std::string {
+            switch (o.media_type) {
+              case AVMEDIA_TYPE_AUDIO:
+                return av_get_sample_fmt_name((AVSampleFormat)(o.format));
+              case AVMEDIA_TYPE_VIDEO:
+                return av_get_pix_fmt_name((AVPixelFormat)(o.format));
+              default:
+                TORCH_INTERNAL_ASSERT(
+                    false,
+                    "FilterGraph is returning unexpected media type: ",
+                    av_get_media_type_string(o.media_type));
+            }
+          })
+      .def_readonly("sample_rate", &OutputStreamInfo::sample_rate)
+      .def_readonly("num_channels", &OutputStreamInfo::num_channels)
+      .def_readonly("width", &OutputStreamInfo::width)
+      .def_readonly("height", &OutputStreamInfo::height)
+      .def_property_readonly(
+          "frame_rate", [](const OutputStreamInfo& o) -> double {
+            if (o.frame_rate.den == 0) {
+              TORCH_WARN(
+                  o.frame_rate.den,
+                  "Invalid frame rate is found: ",
+                  o.frame_rate.num,
+                  "/",
+                  o.frame_rate.den);
+              return -1;
+            }
+            return static_cast<double>(o.frame_rate.num) / o.frame_rate.den;
+          });
   py::class_<SrcStreamInfo>(m, "SourceStreamInfo", py::module_local())
       .def_property_readonly(
           "media_type",

torchaudio/csrc/ffmpeg/stream_reader/sink.cpp

@@ -50,6 +50,7 @@ std::unique_ptr<Buffer> get_buffer(
 std::unique_ptr<FilterGraph> get_filter_graph(
     AVRational input_time_base,
     AVCodecParameters* codecpar,
+    AVRational frame_rate,
     const std::string& filter_description) {
   auto p = std::make_unique<FilterGraph>(codecpar->codec_type);
 
@@ -65,6 +66,7 @@ std::unique_ptr<FilterGraph> get_filter_graph(
       p->add_video_src(
           static_cast<AVPixelFormat>(codecpar->format),
           input_time_base,
+          frame_rate,
           codecpar->width,
           codecpar->height,
           codecpar->sample_aspect_ratio);
@@ -85,13 +87,19 @@ Sink::Sink(
     AVCodecParameters* codecpar_,
     int frames_per_chunk,
     int num_chunks,
+    AVRational frame_rate_,
     const c10::optional<std::string>& filter_description_,
     const torch::Device& device)
     : input_time_base(input_time_base_),
       codecpar(codecpar_),
+      frame_rate(frame_rate_),
       filter_description(filter_description_.value_or(
           codecpar->codec_type == AVMEDIA_TYPE_AUDIO ? "anull" : "null")),
-      filter(get_filter_graph(input_time_base_, codecpar_, filter_description)),
+      filter(get_filter_graph(
+          input_time_base_,
+          codecpar_,
+          frame_rate,
+          filter_description)),
       output_time_base(filter->get_output_timebase()),
       buffer(get_buffer(
           codecpar_->codec_type,
@@ -125,8 +133,13 @@ std::string Sink::get_filter_description() const {
   return filter_description;
 }
 
+FilterGraphOutputInfo Sink::get_filter_output_info() const {
+  return filter->get_output_info();
+}
+
 void Sink::flush() {
-  filter = get_filter_graph(input_time_base, codecpar, filter_description);
+  filter = get_filter_graph(
+      input_time_base, codecpar, frame_rate, filter_description);
   buffer->flush();
 }
 

torchaudio/csrc/ffmpeg/stream_reader/sink.h

@@ -13,6 +13,7 @@ class Sink {
   // Parameters for recreating FilterGraph
   AVRational input_time_base;
   AVCodecParameters* codecpar;
+  AVRational frame_rate;
   std::string filter_description;
   std::unique_ptr<FilterGraph> filter;
   // time_base of filter graph output, used for PTS calc
@@ -25,10 +26,13 @@ class Sink {
       AVCodecParameters* codecpar,
       int frames_per_chunk,
       int num_chunks,
+      AVRational frame_rate,
       const c10::optional<std::string>& filter_description,
       const torch::Device& device);
 
-  std::string get_filter_description() const;
+  [[nodiscard]] std::string get_filter_description() const;
+  [[nodiscard]] FilterGraphOutputInfo get_filter_output_info() const;
+
   int process_frame(AVFrame* frame);
   bool is_buffer_ready() const;
 

torchaudio/csrc/ffmpeg/stream_reader/stream_processor.cpp

@@ -20,6 +20,7 @@ StreamProcessor::StreamProcessor(
 KeyType StreamProcessor::add_stream(
     int frames_per_chunk,
     int num_chunks,
+    AVRational frame_rate,
     const c10::optional<std::string>& filter_description,
     const torch::Device& device) {
   switch (stream->codecpar->codec_type) {
@@ -38,6 +39,7 @@ KeyType StreamProcessor::add_stream(
           stream->codecpar,
           frames_per_chunk,
           num_chunks,
+          frame_rate,
           filter_description,
           device));
   return key;
@@ -60,6 +62,11 @@ std::string StreamProcessor::get_filter_description(KeyType key) const {
   return sinks.at(key).get_filter_description();
 }
 
+FilterGraphOutputInfo StreamProcessor::get_filter_output_info(
+    KeyType key) const {
+  return sinks.at(key).get_filter_output_info();
+}
+
 bool StreamProcessor::is_buffer_ready() const {
   for (const auto& it : sinks) {
     if (!it.second.buffer->is_ready()) {

torchaudio/csrc/ffmpeg/stream_reader/stream_processor.h

@@ -59,6 +59,7 @@ class StreamProcessor {
   KeyType add_stream(
       int frames_per_chunk,
       int num_chunks,
+      AVRational frame_rate,
       const c10::optional<std::string>& filter_description,
       const torch::Device& device);
 
@@ -72,7 +73,9 @@ class StreamProcessor {
   //////////////////////////////////////////////////////////////////////////////
   // Query methods
   //////////////////////////////////////////////////////////////////////////////
-  std::string get_filter_description(KeyType key) const;
+  [[nodiscard]] std::string get_filter_description(KeyType key) const;
+  [[nodiscard]] FilterGraphOutputInfo get_filter_output_info(KeyType key) const;
+
   bool is_buffer_ready() const;
 
   //////////////////////////////////////////////////////////////////////////////

torchaudio/csrc/ffmpeg/stream_reader/stream_reader.cpp

@@ -187,11 +187,27 @@ int64_t StreamReader::num_out_streams() const {
 
 OutputStreamInfo StreamReader::get_out_stream_info(int i) const {
   validate_output_stream_index(i);
-  OutputStreamInfo ret;
   int i_src = stream_indices[i].first;
   KeyType key = stream_indices[i].second;
+  FilterGraphOutputInfo info = processors[i_src]->get_filter_output_info(key);
+
+  OutputStreamInfo ret;
   ret.source_index = i_src;
   ret.filter_description = processors[i_src]->get_filter_description(key);
+  ret.media_type = info.type;
+  ret.format = info.format;
+  switch (info.type) {
+    case AVMEDIA_TYPE_AUDIO:
+      ret.sample_rate = info.sample_rate;
+      ret.num_channels = info.num_channels;
+      break;
+    case AVMEDIA_TYPE_VIDEO:
+      ret.width = info.width;
+      ret.height = info.height;
+      ret.frame_rate = info.frame_rate;
+      break;
+    default:;
+  }
   return ret;
 }
 
@@ -336,8 +352,22 @@ void StreamReader::add_stream(
     processors[i]->set_discard_timestamp(seek_timestamp);
   }
   stream->discard = AVDISCARD_DEFAULT;
+
+  auto frame_rate = [&]() -> AVRational {
+    switch (media_type) {
+      case AVMEDIA_TYPE_AUDIO:
+        return AVRational{0, 1};
+      case AVMEDIA_TYPE_VIDEO:
+        return av_guess_frame_rate(pFormatContext, stream, nullptr);
+      default:
+        TORCH_INTERNAL_ASSERT(
+            false,
+            "Unexpected media type is given: ",
+            av_get_media_type_string(media_type));
+    }
+  }();
   int key = processors[i]->add_stream(
-      frames_per_chunk, num_chunks, filter_desc, device);
+      frames_per_chunk, num_chunks, frame_rate, filter_desc, device);
   stream_indices.push_back(std::make_pair<>(i, key));
 }
 

torchaudio/csrc/ffmpeg/stream_reader/typedefs.h

@@ -101,9 +101,48 @@ struct SrcStreamInfo {
 struct OutputStreamInfo {
   /// The index of the input source stream
   int source_index;
+
+  ///
+  /// The stream media type.
+  ///
+  /// Please see refer to
+  /// [the FFmpeg
+  /// documentation](https://ffmpeg.org/doxygen/4.1/group__lavu__misc.html#ga9a84bba4713dfced21a1a56163be1f48)
+  /// for the available values
+  ///
+  /// @todo Introduce own enum and get rid of FFmpeg dependency
+  ///
+  AVMediaType media_type = AVMEDIA_TYPE_UNKNOWN;
+  int format = -1;
+
   /// Filter graph definition, such as
   /// ``"aresample=16000,aformat=sample_fmts=fltp"``.
-  std::string filter_description;
+  std::string filter_description{};
+
+  /// @name AUDIO-SPECIFIC MEMBERS
+  ///@{
+
+  /// Sample rate
+  double sample_rate = -1;
+
+  /// The number of channels
+  int num_channels = -1;
+
+  ///@}
+
+  /// @name VIDEO-SPECIFIC MEMBERS
+  ///@{
+
+  /// Width
+  int width = -1;
+
+  /// Height
+  int height = -1;
+
+  /// Frame rate
+  AVRational frame_rate{0, 1};
+
+  ///@}
 };
 
 /// Stores decoded frames and metadata

torchaudio/csrc/ffmpeg/stream_writer/encode_process.cpp

@@ -435,6 +435,7 @@ FilterGraph get_video_filter(AVPixelFormat src_fmt, AVCodecContext* codec_ctx) {
   p.add_video_src(
       src_fmt,
       codec_ctx->time_base,
+      codec_ctx->framerate,
       codec_ctx->width,
       codec_ctx->height,
       codec_ctx->sample_aspect_ratio);

torchaudio/io/_stream_reader.py

 from __future__ import annotations
 
 from dataclasses import dataclass
-from typing import BinaryIO, Dict, Iterator, Optional, Tuple, Union
+from typing import BinaryIO, Dict, Iterator, Optional, Tuple, TypeVar, Union
 
 import torch
 import torchaudio
@@ -154,6 +154,80 @@ class OutputStream:
     """Index of the source stream that this output stream is connected."""
     filter_description: str
     """Description of filter graph applied to the source stream."""
+    media_type: str
+    """The type of the stream. ``"audio"`` or ``"video"``."""
+    format: str
+    """Media format. Such as ``"s16"`` and ``"yuv420p"``.
+
+    Commonly found audio values are;
+
+    - ``"u8"``, ``"u8p"``: Unsigned 8-bit unsigned interger.
+    - ``"s16"``, ``"s16p"``: 16-bit signed integer.
+    - ``"s32"``, ``"s32p"``: 32-bit signed integer.
+    - ``"flt"``, ``"fltp"``: 32-bit floating-point.
+
+    .. note::
+
+       `p` at the end indicates the format is `planar`.
+       Channels are grouped together instead of interspersed in memory."""
+
+
+@dataclass
+class OutputAudioStream(OutputStream):
+    """Information about an audio output stream configured with
+    :meth:`~torchaudio.io.StreamReader.add_audio_stream` or
+    :meth:`~torchaudio.io.StreamReader.add_basic_audio_stream`.
+
+    In addition to the attributes reported by :class:`OutputStream`,
+    the following attributes are reported.
+    """
+
+    sample_rate: float
+    """Sample rate of the audio."""
+    num_channels: int
+    """Number of channels."""
+
+
+@dataclass
+class OutputVideoStream(OutputStream):
+    """Information about a video output stream configured with
+    :meth:`~torchaudio.io.StreamReader.add_video_stream` or
+    :meth:`~torchaudio.io.StreamReader.add_basic_video_stream`.
+
+    In addition to the attributes reported by :class:`OutputStream`,
+    the following attributes are reported.
+    """
+
+    width: int
+    """Width of the video frame in pixel."""
+    height: int
+    """Height of the video frame in pixel."""
+    frame_rate: float
+    """Frame rate."""
+
+
+def _parse_oi(i):
+    media_type = i.media_type
+    if media_type == "audio":
+        return OutputAudioStream(
+            source_index=i.source_index,
+            filter_description=i.filter_description,
+            media_type=i.media_type,
+            format=i.format,
+            sample_rate=i.sample_rate,
+            num_channels=i.num_channels,
+        )
+    if media_type == "video":
+        return OutputVideoStream(
+            source_index=i.source_index,
+            filter_description=i.filter_description,
+            media_type=i.media_type,
+            format=i.format,
+            width=i.width,
+            height=i.height,
+            frame_rate=i.frame_rate,
+        )
+    raise ValueError(f"Unexpected media_type: {i.media_type}({i})")
 
 
 def _get_afilter_desc(sample_rate: Optional[int], fmt: Optional[str]):
@@ -351,6 +425,10 @@ _format_video_args = _format_doc(
 )
 
 
+InputStreamTypes = TypeVar("InputStream", bound=SourceStream)
+OutputStreamTypes = TypeVar("OutputStream", bound=OutputStream)
+
+
 @torchaudio._extension.fail_if_no_ffmpeg
 class StreamReader:
     """Fetch and decode audio/video streams chunk by chunk.
@@ -481,29 +559,33 @@ class StreamReader:
         """
         return self._be.get_metadata()
 
-    def get_src_stream_info(self, i: int) -> Union[SourceStream, SourceAudioStream, SourceVideoStream]:
+    def get_src_stream_info(self, i: int) -> InputStreamTypes:
         """Get the metadata of source stream
 
         Args:
             i (int): Stream index.
         Returns:
+            InputStreamTypes:
                 Information about the source stream.
-            If the source stream is audio type, then :class:`SourceAudioStream` returned.
-            If it is video type, then :class:`SourceVideoStream` is returned.
-            Otherwise :class:`SourceStream` class is returned.
+                If the source stream is audio type, then :class:`~torchaudio.io._stream_reader.SourceAudioStream` returned.
+                If it is video type, then :class:`~torchaudio.io._stream_reader.SourceVideoStream` is returned.
+                Otherwise :class:`~torchaudio.io._stream_reader.SourceStream` class is returned.
         """
         return _parse_si(self._be.get_src_stream_info(i))
 
-    def get_out_stream_info(self, i: int) -> OutputStream:
+    def get_out_stream_info(self, i: int) -> OutputStreamTypes:
         """Get the metadata of output stream
 
         Args:
             i (int): Stream index.
         Returns:
-            OutputStream
+            OutputStreamTypes
+                Information about the output stream.
+                If the output stream is audio type, then :class:`~torchaudio.io._stream_reader.OutputAudioStream` returned.
+                If it is video type, then :class:`~torchaudio.io._stream_reader.OutputVideoStream` is returned.
         """
         info = self._be.get_out_stream_info(i)
-        return OutputStream(info.source_index, info.filter_description)
+        return _parse_oi(info)
 
     def seek(self, timestamp: float, mode: str = "precise"):
         """Seek the stream to the given timestamp [second]