FFMPEGython跟踪转码过程

Question

我的问题是基于https://github.com/kkroening/ffmpeg-python/blob/master/examples/show_progress.py 理想情况下，我只想跟踪转码过程，例如0-100，向我的gRPC客户端发送流式处理响应。从技术上讲，我不需要进度条。 如何为ffmpeg子进程提供自己的套接字并处理写入事件

Answer 1

您可以使用-progress pipe:1将“进度”重定向到stdout。
见How to redirect -progress option output of ffmpeg to stderr?

最困难的部分是实际取得百分比的进展

• 按照here所述，首先使用FFprobe计算总帧数
• 执行FFmpeg作为子进程，将-progress重定向到stdout
• 启动从stdout读取文本行的线程。
  线程查找frame=xx，获取帧，并将其放入一个列表（1个元素的列表）
• 执行“主循环”以演示进度读数。
  循环休眠1秒，从队列中读取最后一个元素，并打印进度

代码首先构建一个合成视频文件input.mp4，用作输入

下面是一个“自包含”的代码示例：

import subprocess as sp
import shlex
import json
from threading import Thread
import time


def progress_reader(procs, q):
    while True:
        if procs.poll() is not None:
            break  # Break if FFmpeg sun-process is closed

        progress_text = procs.stdout.readline()  # Read line from the pipe

        # Break the loop if progress_text is None (when pipe is closed).
        if progress_text is None:
            break

        progress_text = progress_text.decode("utf-8")  # Convert bytes array to strings

        # Look for "frame=xx"
        if progress_text.startswith("frame="):
            frame = int(progress_text.partition('=')[-1])  # Get the frame number
            q[0] = frame  # Store the last sample


# Build synthetic video for testing:
################################################################################
sp.run(shlex.split('ffmpeg -y -f lavfi -i testsrc=size=320x240:rate=30 -f lavfi -i sine=frequency=400 -f lavfi -i sine=frequency=1000 -filter_complex amerge -vcodec libx265 -crf 17 -pix_fmt yuv420p -acodec aac -ar 22050 -t 30 input.mp4'))
################################################################################


# Use FFprobe for counting the total number of frames
################################################################################
# Execute ffprobe (to show streams), and get the output in JSON format
# Actually counts packets instead of frames but it is much faster
# https://stackoverflow.com/questions/2017843/fetch-frame-count-with-ffmpeg/28376817#28376817
data = sp.run(shlex.split('ffprobe -v error -select_streams v:0 -count_packets -show_entries stream=nb_read_packets -of csv=p=0 -of json input.mp4'), stdout=sp.PIPE).stdout
dict = json.loads(data)  # Convert data from JSON string to dictionary
tot_n_frames = float(dict['streams'][0]['nb_read_packets'])  # Get the total number of frames.
################################################################################

# Execute FFmpeg as sub-process with stdout as a pipe
# Redirect progress to stdout using -progress pipe:1 arguments
process = sp.Popen(shlex.split('ffmpeg -y -loglevel error -i input.mp4 -acodec libvorbis -vcodec libvpx-vp9 -crf 20 -pix_fmt yuv420p -progress pipe:1 output.webm'), stdout=sp.PIPE)

q = [0]  # We don't really need to use a Queue - use a list of of size 1
progress_reader_thread = Thread(target=progress_reader, args=(process, q))  # Initialize progress reader thread
progress_reader_thread.start()  # Start the thread

while True:
    if process.poll() is not None:
        break  # Break if FFmpeg sun-process is closed

    time.sleep(1)  # Sleep 1 second (do some work...)

    n_frame = q[0]  # Read last element from progress_reader - current encoded frame
    progress_percent = (n_frame/tot_n_frames)*100   # Convert to percentage.
    print(f'Progress [%]: {progress_percent:.2f}')  # Print the progress


process.stdout.close()          # Close stdin pipe.
progress_reader_thread.join()   # Join thread
process.wait()                  # Wait for FFmpeg sub-process to finish

---

注:

• 代码示例假定ffmpeg和ffprobe位于可执行路径中

---

样本输出：

Progress [%]: 7.33
Progress [%]: 16.00
Progress [%]: 24.67
Progress [%]: 33.33
Progress [%]: 42.13
Progress [%]: 50.40
Progress [%]: 58.80
Progress [%]: 67.20
Progress [%]: 75.60
Progress [%]: 84.00
Progress [%]: 92.40
Progress [%]: 100.00