GStreamer Windows Audio Thread Priority hack

prio_hack.py

#
# Proof of concept to hack around lack of thread priority in GStreamer on
# Windows. See https://bugzilla.gnome.org/show_bug.cgi?id=781998
#

from __future__ import print_function

from ctypes.wintypes import BOOL, DWORD, HANDLE, LPCWSTR
import ctypes as C

avrt_dll = C.windll.LoadLibrary("avrt.dll")
AvSetMmThreadCharacteristics = avrt_dll.AvSetMmThreadCharacteristicsW
AvSetMmThreadCharacteristics.argtypes = [LPCWSTR, C.POINTER(DWORD)]
AvSetMmThreadCharacteristics.restype = HANDLE

AvRevertMmThreadCharacteristics = avrt_dll.AvRevertMmThreadCharacteristics
AvRevertMmThreadCharacteristics.argtypes = [HANDLE]
AvRevertMmThreadCharacteristics.restype = BOOL

GetCurrentThreadId = C.windll.LoadLibrary("kernel32.dll").GetCurrentThreadId
GetCurrentThreadId.argtypes = []
GetCurrentThreadId.restype = DWORD

#
# GST playbin boilerplate
#

from os.path import abspath
import sys

#import os
#os.environ.setdefault('GST_DEBUG_DUMP_DOT_DIR', '.')

from gi.repository import Gst, GObject

def on_stream_status(bus, message):
    status = message.parse_stream_status()
    
    # A gstreamer thread starts
    if status.type == Gst.StreamStatusType.ENTER:
        obj = message.get_stream_status_object()
        
        # note that we use "Pro Audio" because it gives a higher priority, and
        # that's what Chrome does anyways...
        unused = DWORD()
        obj.task_handle = AvSetMmThreadCharacteristics("Pro Audio", C.byref(unused))
    
    # A gstreamer thread ends
    elif status.type == Gst.StreamStatusType.LEAVE:
        obj = message.get_stream_status_object()
        task_handle = getattr(obj, 'task_handle', None)
        if task_handle:
            AvRevertMmThreadCharacteristics(task_handle)
        

if __name__ == '__main__':
    Gst.init(None)

    player = Gst.ElementFactory.make('playbin')
    player.props.uri = 'file:///%s' % abspath(sys.argv[1]).replace('\\', '/')
    
    bus = player.get_bus()
    bus.connect('sync-message::stream-status', on_stream_status)
    bus.enable_sync_message_emission()
    
    player.set_state(Gst.State.PLAYING)
    
    ml = GObject.MainLoop()
    ml.run()