docstr: Audio/image tensors are saved as single video
docstr_tok: ["Audio\/image","tensors","are","saved","as","single","video"]
code: 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)
  
imports: import io
  import math
  import torch
  import torchaudio
  from parameterized import parameterized, parameterized_class
  from torchaudio.io import CodecConfig, StreamReader, StreamWriter
  from torchaudio_unittest.common_utils import get_asset_path, get_sinusoid, nested_params, rgb_to_yuv_ccir, skipIfNoFFmpeg, skipIfNoModule, TempDirMixin, TorchaudioTestCase
  from .common import lt42
label_desc: Use image node_id 9 for calling the StreamWriterInterfaceTest obj's underlying member method code with example usage: obj.test_valid_audio_video_muxer() without return types