ffmpeg 中的多个命名管道

Question

这个问题是这个问题的后续

在我的应用程序中，我想修改各种 mp3，然后将它们混合在一起。 我知道我可以使用 FFmpeg 中的单个命令行来完成它，但它最终会变得非常混乱，因为我需要在每个样本上使用各种过滤器并且我有五个。 我的想法是单独编辑每个样本，将它们保存到 pipe 中，最后混合它们。

import subprocess
import os

def create_pipes():
    os.mkfifo("pipe1")
    os.mkfifo("pipe2")

    
def create_samp():   
    sample= subprocess.run(["ffmpeg", "-i", "https://freesound.org/data/previews/186/186942_2594536-hq.mp3", \
                            "-af", "adelay=15000|15000", "-f", "mp3", "pipe:pipe1"], stdout=subprocess.PIPE).stdout
    return(sample)

def create_samp_2():   
    sample= subprocess.run(["ffmpeg", "-i", "https://freesound.org/data/previews/370/370934_6399962-lq.ogg", \
                            "-af", "adelay=1000|1000", "-f", "mp3", "pipe:pipe2"], stdout=subprocess.PIPE).stdout
    return(sample)


def record(samp, samp_2):  
    process = subprocess.Popen(["ffmpeg", "-y", '-f', 'mp3', \
                                "-i", "https://cdns-preview-b.dzcdn.net/stream/c-b0b684fe962f93dc43f1f7ea493683a1-3.mp3", \
                                "-i", "pipe1", \
                                "-i", "pipe2", \
                                "-filter_complex", "amix=inputs=3:duration=longest", "output.mp3"], stdin=subprocess.PIPE)

    process.stdin.write(samp)  
    process.stdin.write(samp_2)
    process.stdin.close()  
    process.wait()

create_pipes()
samp = create_samp()
samp_2 = create_samp_2()
record(samp, samp_2)

当我运行脚本时， create_samp()和create_samp2()运行良好。 但是我运行record() ，程序卡住没有错误消息，所以我无法弄清楚问题是什么。

Answer 1

使用命名管道（仅限 Linux）：

当有两个或更多输入流（需要从 memory 缓冲区通过管道传输）时，需要命名管道。
使用命名管道一点也不简单……

从 FFmpeg 的角度来看，命名管道就像（不可搜索的）输入文件。

在 Python 中使用命名管道（在 Linux 中）：
假设pipe1是“命名管道”的名称（例如pipe1 = "audio_pipe1" ）。

1. 创建一个“命名管道”：

    os.mkfifo(pipe1)

2. 将 pipe 作为“只写”文件打开：

    fd_pipe = os.open(pipe_name, os.O_WRONLY) # fd_pipe1 is a file descriptor (an integer).

3. 将数据分小块写入 pipe。
   根据这篇文章，大多数 Linux 系统中 pipe 的默认缓冲区大小为 64KBytes。
   由于数据大于 65536 字节，我们需要将数据分小块写入 pipe。
   我决定使用 1024 字节的任意块大小。
   Pipe写操作是“阻塞”操作。
   我通过使用“作家”线程解决了它：

    def writer(data, pipe_name, chunk_size): # Open the pipes as opening "low level IO" files (open for "open for writing only"). fd_pipe = os.open(pipe_name, os.O_WRONLY) # fd_pipe1 is a file descriptor (an integer) for i in range(0, len(data), chunk_size): # Write to named pipe as writing to a "low level IO" file (but write the data in small chunks). os.write(fd_pipe, data[i:chunk_size+i]) # Write 1024 bytes of data to fd_pipe

4. 关闭 pipe：

    os.close(fd_pipe)

5. 删除（取消链接）命名的 pipe：

    os.unlink(pipe1)

---

这是上一篇文章中的示例，使用了两个命名管道：

import subprocess
import os
from threading import Thread


def create_samp():
    # Read audio stream from https://freesound.org/data/previews/186/186942_2594536-hq.mp3
    # Apply adelay audio filter.
    # Encode the audio in mp3 format.
    # FFmpeg output is passed to stdout pipe, and stored in sample bytes array.
    sample1 = subprocess.run(["ffmpeg", "-i", "https://freesound.org/data/previews/186/186942_2594536-hq.mp3",
                              "-af", "adelay=15000|15000", "-f", "mp3", "pipe:"], stdout=subprocess.PIPE).stdout

    # Read second audio sample from https://cdns-preview-b.dzcdn.net/stream/c-b0b684fe962f93dc43f1f7ea493683a1-3.mp3
    sample2 = subprocess.run(["ffmpeg", "-i", "https://cdns-preview-b.dzcdn.net/stream/c-b0b684fe962f93dc43f1f7ea493683a1-3.mp3",
                              "-f", "mp3", "pipe:"], stdout=subprocess.PIPE).stdout

    return sample1, sample2


def writer(data, pipe_name, chunk_size):
    # Open the pipes as opening files (open for "open for writing only").
    fd_pipe = os.open(pipe_name, os.O_WRONLY)  # fd_pipe1 is a file descriptor (an integer)

    for i in range(0, len(data), chunk_size):
        # Write to named pipe as writing to a file (but write the data in small chunks).
        os.write(fd_pipe, data[i:chunk_size+i])  # Write 1024 bytes of data to fd_pipe

    # Closing the pipes as closing files.
    os.close(fd_pipe)


def record(samp1, samp2):
    # Names of the "Named pipes"
    pipe1 = "audio_pipe1"
    pipe2 = "audio_pipe2"

    # Create "named pipes".
    os.mkfifo(pipe1)
    os.mkfifo(pipe2)

    # Open FFmpeg as sub-process
    # Use two audio input streams:
    # 1. Named pipe: "audio_pipe1"
    # 2. Named pipe: "audio_pipe2"
    # Merge the two audio streams using amix audio filter.
    # Store the result to output file: output.mp3
    process = subprocess.Popen(["ffmpeg", "-y", '-f', 'mp3',
                                "-i", pipe1,
                                "-i", pipe2,
                                "-filter_complex", "amix=inputs=2:duration=longest", "output.mp3"],
                                stdin=subprocess.PIPE)

    # Initialize two "writer" threads (each writer writes data to named pipe in chunks of 1024 bytes).
    thread1 = Thread(target=writer, args=(samp1, pipe1, 1024))  # thread1 writes samp1 to pipe1
    thread2 = Thread(target=writer, args=(samp2, pipe2, 1024))  # thread2 writes samp2 to pipe2

    # Start the two threads
    thread1.start()
    thread2.start()

    # Wait for the two writer threads to finish
    thread1.join()
    thread2.join()

    process.wait()  # Wait for FFmpeg sub-process to finish

    # Remove the "named pipes".
    os.unlink(pipe1)
    os.unlink(pipe2)


sampl1, sampl2 = create_samp()
record(sampl1, sampl2)

---

更新：

使用 class 的相同解决方案：
使用 class（“ NamedPipeWriter ”类）实现解决方案更优雅一些。
class 继承了线程 class，并覆盖run方法。

您可以创建多个对象的列表，并在循环中迭代它们（而不是为每个新输入流复制代码）。

这是使用 class 的相同解决方案：

import subprocess
import os
import stat
from threading import Thread


def create_samp():
    # Read audio stream from https://freesound.org/data/previews/186/186942_2594536-hq.mp3
    # Apply adelay audio filter.
    # Encode the audio in mp3 format.
    # FFmpeg output is passed to stdout pipe, and stored in sample bytes array.
    sample1 = subprocess.run(["ffmpeg", "-i", "https://freesound.org/data/previews/186/186942_2594536-hq.mp3",
                              "-af", "adelay=15000|15000", "-f", "mp3", "pipe:"], stdout=subprocess.PIPE).stdout

    # Read second audio sample from https://cdns-preview-b.dzcdn.net/stream/c-b0b684fe962f93dc43f1f7ea493683a1-3.mp3
    sample2 = subprocess.run(["ffmpeg", "-i", "https://cdns-preview-b.dzcdn.net/stream/c-b0b684fe962f93dc43f1f7ea493683a1-3.mp3",
                              "-f", "mp3", "pipe:"], stdout=subprocess.PIPE).stdout

    return sample1, sample2


class NamedPipeWriter(Thread):
    """ Write data (in small chunks) to a named pipe using a thread """

    def __init__(self, pipe_name, data):
        """ Initialization - get pipe name and data to be written """
        super().__init__()
        self._pipe_name = pipe_name
        self._chunk_size = 1024
        self._data = data
        

    def run(self):
        """ Open the pipe, write data in small chunks and close the pipe """
        chunk_size = self._chunk_size
        data = self._data

        # Open the pipes as opening files (open for "open for writing only").
        fd_pipe = os.open(self._pipe_name, os.O_WRONLY)  # fd_pipe1 is a file descriptor (an integer)

        for i in range(0, len(data), chunk_size):
            # Write to named pipe as writing to a file (but write the data in small chunks).
            os.write(fd_pipe, data[i:chunk_size+i])  # Write 1024 bytes of data to fd_pipe

        # Closing the pipes as closing files.
        os.close(fd_pipe)


    

def record(samp1, samp2):
    # Names of the "Named pipes"
    pipe1 = "audio_pipe1"
    pipe2 = "audio_pipe2"

    # Create "named pipes".
    if not stat.S_ISFIFO(os.stat(pipe1).st_mode):
        os.mkfifo(pipe1)  # Create the pipe only if not exist.

    if not stat.S_ISFIFO(os.stat(pipe2).st_mode):
        os.mkfifo(pipe2)

    # Open FFmpeg as sub-process
    # Use two audio input streams:
    # 1. Named pipe: "audio_pipe1"
    # 2. Named pipe: "audio_pipe2"
    # Merge the two audio streams using amix audio filter.
    # Store the result to output file: output.mp3
    process = subprocess.Popen(["ffmpeg", "-y", '-f', 'mp3',
                                "-i", pipe1,
                                "-i", pipe2,
                                "-filter_complex", "amix=inputs=2:duration=longest", "output.mp3"],
                                stdin=subprocess.PIPE)

    # Initialize two "writer" threads (each writer writes data to named pipe in chunks of 1024 bytes).
    named_pipe_writer1 = NamedPipeWriter(pipe1, samp1)
    named_pipe_writer2 = NamedPipeWriter(pipe2, samp2)

    # Start the two threads
    named_pipe_writer1.start()
    named_pipe_writer2.start()

    # Wait for the two writer threads to finish
    named_pipe_writer1.join()
    named_pipe_writer1.join()

    process.wait()  # Wait for FFmpeg sub-process to finish

    # Remove the "named pipes".
    os.unlink(pipe1)
    os.unlink(pipe2)


sampl1, sampl2 = create_samp()
record(sampl1, sampl2)

---

笔记：

• 该代码在 Ubuntu 18.04（在虚拟机中）中进行了测试。