我发现获得动态f的唯一方法来自子进程的eedback /输出是使用类似pexpect的东西：

 ＃！ / usr / bin / python 

 import pexpect 

 cmd =foo.sh
 thread = pexpect.spawn（cmd）
 printstarted ％s％cmd 
 cpl = thread.compile_pattern_list（[pexpect.EOF，
'waiting（\d +）']）
 while True：
i = thread.expect_list cpl，timeout = None）
如果i == 0：＃EOF 
打印子进程退出
 break 
 elif i == 1：
 waited_time = thread.match.group（1）
打印子进程等待％d秒％int（waited_time）
 thread.close（）
 

被调用的子进程foo.sh只是等待10到20秒之间的随机时间，这里是它的代码：

 ＃！ / bin / sh 

 n = 5 
 while [$ n -gt 0]; do 
 ns =`date +％N` 
p =`expr $ ns％10 + 10` 
 sleep $ p 
 echo等待$ p 
n =`expr $ n  -  1` 
 done 
 

你将要使用一些与输出您从ffmpeg获得，并对其进行某种计算以显示进度条，但这至少将使您得到ffmpeg的无缓冲输出。

I've looked at a number of questions but still can't quite figure this out. I'm using PyQt, and am hoping to run ffmpeg -i file.mp4 file.avi and get the output as it streams so I can create a progress bar.

I've looked at these questions: Can ffmpeg show a progress bar? catching stdout in realtime from subprocess

I'm able to see the output of a rsync command, using this code:

import subprocess, time, os, sys

cmd = "rsync -vaz -P source/ dest/"
p, line = True, 'start'


p = subprocess.Popen(cmd,
                     shell=True,
                     bufsize=64,
                     stdin=subprocess.PIPE,
                     stderr=subprocess.PIPE,
                     stdout=subprocess.PIPE)

for line in p.stdout:
    print("OUTPUT>>> " + str(line.rstrip()))
    p.stdout.flush()

But when I change the command to ffmpeg -i file.mp4 file.avi I receive no output. I'm guessing this has something to do with stdout / output buffering, but I'm stuck as to how to read the line that looks like

frame=   51 fps= 27 q=31.0 Lsize=     769kB time=2.04 bitrate=3092.8kbits/s

Which I could use to figure out progress.

Can someone show me an example of how to get this info from ffmpeg into python, with or without the use of PyQt (if possible)

---

EDIT: I ended up going with jlp's solution, my code looked like this:

#!/usr/bin/python
import pexpect

cmd = 'ffmpeg -i file.MTS file.avi'
thread = pexpect.spawn(cmd)
print "started %s" % cmd
cpl = thread.compile_pattern_list([
    pexpect.EOF,
    "frame= *\d+",
    '(.+)'
])
while True:
    i = thread.expect_list(cpl, timeout=None)
    if i == 0: # EOF
        print "the sub process exited"
        break
    elif i == 1:
        frame_number = thread.match.group(0)
        print frame_number
        thread.close
    elif i == 2:
        #unknown_line = thread.match.group(0)
        #print unknown_line
        pass

Which gives this output:

started ffmpeg -i file.MTS file.avi
frame=   13
frame=   31
frame=   48
frame=   64
frame=   80
frame=   97
frame=  115
frame=  133
frame=  152
frame=  170
frame=  188
frame=  205
frame=  220
frame=  226
the sub process exited

Perfect!

The only way I've found to get dynamic feedback/output from a child process is to use something like pexpect:

#! /usr/bin/python

import pexpect

cmd = "foo.sh"
thread = pexpect.spawn(cmd)
print "started %s" % cmd
cpl = thread.compile_pattern_list([pexpect.EOF,
                                   'waited (\d+)'])
while True:
    i = thread.expect_list(cpl, timeout=None)
    if i == 0: # EOF
        print "the sub process exited"
        break
    elif i == 1:
        waited_time = thread.match.group(1)
        print "the sub process waited %d seconds" % int(waited_time)
thread.close()

the called sub process foo.sh just waits a random amount of time between 10 and 20 seconds, here's the code for it:

#! /bin/sh

n=5
while [ $n -gt 0 ]; do
    ns=`date +%N`
    p=`expr $ns % 10 + 10`
    sleep $p
    echo waited $p
    n=`expr $n - 1`
done

You'll want to use some regular expression that matches the output you're getting from ffmpeg and does some kind of calculation on it to show the progress bar, but this will at least get you the unbuffered output from ffmpeg.