Gstreamer+python：运行时添加和移除音频源

Question

我正在做一个示例的python脚本，最初是在这里找到的：在运行时向GStreamer管道添加和移除音频源。这个脚本的目的是让它能够在管道运行时插入和移除音频源，但在源和添加器之间加一个audioconvert元素。这样做是因为在更一般的情况下，Adder希望接收到的音频流格式是一样的。

下面是代码；我们创建了两个生成器（发声器）。第一个发出1000Hz的音调，并等待回车键。第二个是500Hz的音调，在按下回车键后会和第一个音调合成。再次按下回车键时，只有第二个生成器的声音能被听到。

#!/usr/bin/python

import gobject;
gobject.threads_init()
import gst

# THE FOLLOWING FUNCTION IS A REWORK OF THE ORIGINAL, STILL DOING THE JOB

def create_raw_audiotest_signal(pipe, freq, adder):
  # create buzzer of a given freq
  buzzer = gst.element_factory_make("audiotestsrc","buzzer%d" % freq)
  buzzer.set_property("freq",freq)
  pipe.add(buzzer)
  buzzersrc=buzzer.get_pad("src")
  # Gather a request sink pad on the mixer
  sinkpad=adder.get_request_pad("sink%d")
  # .. and connect it to the buzzer
  buzzersrc.link(sinkpad)
  return buzzer, buzzersrc, sinkpad

# THIS IS A MODIFIED VERSION, NOT WORKING, THAT JUST PUTS AN AUDIOCONVERT
# ELEMENT BETWEEN THE GENERATOR AND THE ADDER.

def create_audiotest_signal_with_converter(pipe, freq, adder):
    # create buzzer of a given freq
    buzzer = gst.element_factory_make("audiotestsrc","buzzer%d" % freq)
    buzzer.set_property("freq",freq)
    # add a converter because adder wants inputs with the same format.
    ac = gst.element_factory_make("audioconvert", "ac%d" % freq)
    pipe.add(buzzer, ac)
    # link the buzzer with the converter ...
    buzzer.link(ac)
    buzzersrc=buzzer.get_pad("src")
    # Gather a request sink pad on the mixer
    sinkpad=adder.get_request_pad("sink%d")
    # and then the converter to the adder
    ac.get_pad('src').link(sinkpad)
    return buzzer, buzzersrc, sinkpad

if __name__ == "__main__":
  # First create our pipeline
  pipe = gst.Pipeline("mypipe")

  # Create a software mixer with "Adder"
  adder = gst.element_factory_make("adder","audiomixer")
  pipe.add(adder)

  # Create the first buzzer..
  #buzzer1, buzzersrc1, sinkpad1 = create_raw_audiotest_signal(pipe, 1000, adder)
  buzzer1, buzzersrc1, sinkpad1 = create_audiotest_signal_with_converter(pipe, 1000, adder)

  # Add some output
  output = gst.element_factory_make("autoaudiosink", "audio_out")
  pipe.add(output)
  adder.link(output)

  # Start the playback
  pipe.set_state(gst.STATE_PLAYING)

  raw_input("1kHz test sound. Press <ENTER> to continue.")

  # Get another generator
  #buzzer2, buzzersrc2, sinkpad2 = create_raw_audiotest_signal(pipe, 500, adder)
  buzzer2, buzzersrc2, sinkpad2 = create_audiotest_signal_with_converter(pipe, 500, adder)

  # Start the second buzzer (other ways streaming stops because of starvation)
  buzzer2.set_state(gst.STATE_PLAYING)

  raw_input("1kHz + 500Hz test sound playing simoultenously. Press <ENTER> to continue.")

  # Before removing a source, we must use pad blocking to prevent state changes
  buzzersrc1.set_blocked(True)
  # Stop the first buzzer
  buzzer1.set_state(gst.STATE_NULL)
  # Unlink from the mixer
  buzzersrc1.unlink(sinkpad2)
  # Release the mixers first sink pad
  adder.release_request_pad(sinkpad1)
  # Because here none of the Adder's sink pads block, streaming continues

  raw_input("Only 500Hz test sound. Press <ENTER> to stop.")

如果在两个调用中用create_raw_audiotest_signal替换create_audiotest_signal_with_converter，当然是可以正常工作的。如果混合使用这两者，也能工作，但会有不必要的额外延迟。最有趣的情况是，当在两个调用中都使用audioconvert时，gtk在第一次按下回车键时会阻塞。

有没有人有什么建议？我哪里做错了？谢谢大家。

multimedia programming audio processing GStreamer audio source management audioconvert pipeline manipulation real-time audio signal generation

Gstreamer+python：运行时添加和移除音频源

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