[Beta] New Video Reader API
This release introduces a new video reading abstraction, which gives more fine-grained control of iteration over videos. It supports image and audio, and implements an iterator interface so that it is interoperable with other the python libraries such as itertools.
```python
from torchvision.io import VideoReader
stream indicates if reading from audio or video
reader = VideoReader('path_to_video.mp4', stream='video')
can change the stream after construction
via reader.set_current_stream
to read all frames in a video starting at 2 seconds
for frame in reader.seek(2):
    # frame is a dict with "data" and "pts" metadata
    print(frame["data"], frame["pts"])
because reader is an iterator you can combine it with
itertools
from itertools import takewhile, islice
read 10 frames starting from 2 seconds
for frame in islice(reader.seek(2), 10):
    pass
or to return all frames between 2 and 5 seconds
for frame in takewhile(lambda x: x["pts"] < 5, reader):