Break reference cycle in StreamContainer.get()

[lgeiger]

StreamContainer.get() defines a process function which binds self. This causes a reference cycle putting strain on the Garbage collector. This can be reproduced with the following code:

import gc
import av
from tests.common import fate_suite


def demux(video):
    with av.open(video) as container:
        for packet in container.demux(video=0):
            pass


video = fate_suite("h264/interlaced_crop.mp4")
gc.collect()
gc.disable()
demux(video)
print("GC collected:", gc.collect())

version	GC collected objects
main	399
This PR	0

We could also break this reference cycle by setting process = None after it's use in StreamContainer.get() but I think moving it into a separate method which yields is cleaner.

@oakaigh can you check whether this fixes #2219 for you?

[oakaigh]

@lgeiger Don't have the bandwidth to test this right now; In the meantime, wouldn't it be better to add the code to the tests and run it through CI?