URL流在Python中开始播放时的回调函数

Question

我目前正在用Python为一个树莓Pi制作一个互联网广播播放器。功能很简单：在用户输入时，程序从预定义的列表中随机选择一个URL无线电流，并开始通过omxplayer将其作为子进程播放

这是我的密码：

import simpleaudio as sa
import random
import sys, termios, tty, os
import subprocess

radioList = ["https://edge126.rcs-rds.ro/profm/profm.mp3", "https://live.guerrillaradio.ro:8443/guerrilla.aac", "http://aska.ru-hoster.com:8053/autodj", "https://live.rockfm.ro/rockfm.aacp", "https://live.magicfm.ro/magicfm.aacp", "http://zuicast.digitalag.ro:9420/zu"]

class AudioPlayer: # used only for playing noise.wav until radio stream starts 
    def __init__(self):
        self.play_obj = None

    def play(self, filename):
        if not self.is_done():
            self.play_obj.stop()

        wave_obj = sa.WaveObject.from_wave_file(filename)
        self.play_obj = wave_obj.play()
        
    def stop(self):
        self.play_obj.stop()

    def is_done(self):
        if self.play_obj:
            return not self.play_obj.is_playing()
        return True

def getRandomURL(radioList): # returns random URL from provided list
    r = random.randint(1, len(radioList)) - 1
    return radioList[r]

def getch(): # reads input character from stdin
    fd = sys.stdin.fileno()
    old_settings = termios.tcgetattr(fd)
    try:
        tty.setraw(sys.stdin.fileno())
        ch = sys.stdin.read(1)

    finally:
        termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
    return ch


noisePlayer = AudioPlayer() # create audio instance
omxprocess = ""


while True:
    char = getch()
        
    if(char == "p"):
        if omxprocess != "":
            omxprocess.kill()
        omxprocess = subprocess.Popen(['omxplayer', getRandomURL(radioList)], stdin=subprocess.PIPE) # you should change 'omxplayer' to 'cvlc' or 'mplayer' if you're not running this code on a raspi
        
        # noisePlayer.play("noise.wav") # this file should be played from the moment the above process is started until the radio stream is actually loaded and starts playing
        
    if(char == "x"):
        if omxprocess != "":
            omxprocess.kill()
        exit()

但是，我在Raspberry Pi Zero上运行此代码，通常需要3-4秒（甚至更长）才能开始播放流。我想做的是播放一个本地音频文件（本例中为noise.wav，可在：https://www.random.org/audio-noise/生成），直到流开始播放的确切时刻，这样在通勤电台之间就不会有无声死区。我的问题是，我不知道如何实现这一点，因为我没有发现omxplayer、vlc或mplayer在媒体流实际加载并开始播放时触发的任何信号或事件

然而，我确实发现omxplayer向stdout发送了一些信息，这些信息会在流开始播放时被打印出来（对于vlc和mplayer也是如此）。下面是一个例子：

pi@raspi:~ $ omxplayer https://live.rockfm.ro/rockfm.aacp
Audio codec aac channels 2 samplerate 44100 bitspersample 16
Subtitle count: 0, state: off, index: 1, delay: 0
have a nice day ;)
pi@raspi:~ $

我很好奇是否有某种方法可以使用此输出作为触发器来停止播放noisePlayer（使用noisePlayer.stop（）），或者是否有其他方法可以在无线电波开始播放时触发noisePlayer.stop（）？我尝试过的一个选项是使用线程模块中的计时器功能，但它通常会覆盖无线电流，从而可以更快地开始播放：

        Timer(0.5, noisePlayer.play, ["noise.wav"]).start()
        Timer(1.5, noisePlayer.stop).start()

我找到的关于我的担忧的唯一一篇文章是：Python communicate with omxplayer 然而，它并没有完全回答我的问题

如果有人能给这个问题一个确切的实施方案，或者如何解决这个问题的解决方案，我将非常感激，因为我根本无法理解：）

Answer 1

您只需要为stdout包含一个subprocess.PIPE。
如果您希望测试stderr，还可以包括一个stderr

import subprocess as sub

stdout, stderr  ##  forward declarations so that these exist within scope

while True:
    char = getch()

    if(char == "p"):
        if omxprocess != "":
            omxprocess.kill()
            command = ['omxplayer', getRandomURL(radioList)]
        omxprocess = sub.Popen(command, stdin=sub.PIPE, stdout=sub.PIPE, stderr=sub.PIPE)

        stdout, stderr = omxprocess.communicate()

        noisePlayer.play("noise.wav")

    if stdout or stderr: noisePlayer.stop()

    if(char == "x"):
        if omxprocess != "":
            omxprocess.kill()
        exit()