ffmpeg python跟踪转码过程

Question

我的问题基于https://github.com/kkroening/ffmpeg-python/blob/master/examples/show_progress.py理想情况下，我只想跟踪代码转换过程，例如0-100，向我的gRPC客户端发出流式收益响应。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其中的写入事件？

Answer 1

您可以重定向"进步；使用CCD_ 2发送到CCD_
请参阅如何将ffmpeg的progress选项输出重定向到stderr？

最困难的部分是实际获得百分比进度。

• 首先使用此处所述的FFprobe计算帧总数
• 执行FFmpeg作为子进程，将-progress重定向到stdout
• 启动一个从stdout中读取文本行的线程
  线程查找frame=xx，获取帧，并将其放入列表(1个元素的列表(中
• 执行一个"；主环路"；用于演示进度读数
  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。

这里有一个"；自给自足"；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：

• 代码示例假设ffmpeg和ffprobe在可执行路径中

---

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