Approach to get currently playing media's thumbnail on Windows only works once per Python instance

Question

I'm trying to get the thumbnail of the currently playing media on windows, and thanks to this answer (https://stackoverflow.com/a/66037406/15491505) i got quite far, however I'm facing a strange issue where in get_thumbnail() the variable byte_buffer always ends up being 0 in length after the first run... as in the first time I call it I get back the thumbnail perfectly, but all further calls end up failing...

This is what I have so far:

from winrt.windows.media.control import GlobalSystemMediaTransportControlsSessionManager as MediaManager
from winrt.windows.storage.streams import DataReader, Buffer, InputStreamOptions
from io import BytesIO
from PIL import Image
import asyncio


async def get_thumbnail():
    sessions = await MediaManager.request_async()
    current_session = sessions.get_current_session()

    if current_session:
        properties = await current_session.try_get_media_properties_async()
        media_info = {song_attr: properties.__getattribute__(song_attr) for song_attr in dir(properties) if song_attr[0] != '_'}

        if media_info.get('thumbnail'):
            thumb_stream_ref = media_info['thumbnail']
            thumb_read_buffer = Buffer(5000000)

            readable_stream = await thumb_stream_ref.open_read_async()
            readable_stream.read_async(thumb_read_buffer, thumb_read_buffer.capacity, InputStreamOptions.READ_AHEAD)

            buffer_reader = DataReader.from_buffer(thumb_read_buffer)
            byte_buffer = buffer_reader.read_bytes(thumb_read_buffer.length)

            binary = BytesIO()
            binary.write(bytearray(byte_buffer))
            binary.seek(0)
            print(len(bytearray(byte_buffer)))

            img = Image.open(binary)
            return img


thumbnail = asyncio.run(get_thumbnail())
thumbnail.show()
# This will work

thumbnail2 = asyncio.run(get_thumbnail())
thumbnail2.show()
# This will not

Example output:

C:\Users\willy\Desktop>test.py
117672
0
Traceback (most recent call last):
  File "C:\Users\willy\Desktop\test.py", line 39, in <module>
    thumbnail2 = asyncio.run(get_thumbnail())
  File "C:\Python38\lib\asyncio\runners.py", line 44, in run
    return loop.run_until_complete(main)
  File "C:\Python38\lib\asyncio\base_events.py", line 616, in run_until_complete
    return future.result()
  File "C:\Users\willy\Desktop\test.py", line 31, in get_thumbnail
    img = Image.open(binary)
  File "C:\Python38\lib\site-packages\PIL\Image.py", line 2930, in open
    raise UnidentifiedImageError(
PIL.UnidentifiedImageError: cannot identify image file <_io.BytesIO object at 0x00000278D2FB3B30>

Answer 1

Solution

Simply await the result of the readable_stream.read_async(...) call:

...
readable_stream = await thumb_stream_ref.open_read_async()
await readable_stream.read_async(thumb_read_buffer, thumb_read_buffer.capacity, InputStreamOptions.READ_AHEAD)

buffer_reader = DataReader.from_buffer(thumb_read_buffer)
...

The thumbnail should now be successfully displayed each time.

Debugging process

(for anyone interested and for similar bugs in the future)

After break-pointing your code, it appeared that, on the second call of get_thumbnail(), byte_buffer was left empty. This indicated that the thumb_read_buffer was not being populated correctly from the stream.

Interestingly, when single-stepping the code instead, the image displayed both times. This suggested to me that maybe an asynchronous function call wasn't being awaited.

Turns out .read_async() (as the function name suggests) is an asynchronous operation in winrt (see IInputStream.ReadAsync on learn.microsoft.com). Hence, awaiting its execution fixed the problem of the empty thumb_read_buffer.