如何使用 Python 捕获 x265.exe 的实时命令行输出？

Question

我想为 x265.exe 编写一个 GUI，它呈现更好（更人性化）的实时进度。

这是我用来捕获子进程输出的代码：

import subprocess

cmd = r'ping www.baidu.com -n 4'
popen = subprocess.Popen(cmd, stdout = subprocess.PIPE ,stderr=subprocess.STDOUT ,shell=True)
while True:
    next_line = popen.stdout.readline()
    if next_line == b'' and popen.poll() != None:
        break
    else:
        print(next_line.decode('ascii').replace('\r\n','\n') , end='')

与'ping'完美搭配。

但是，当我切换到 'x265' 命令时，一切都变成了有线。

例如，如果我将前面的 code.Theoretically 中的字符串变量 'cmd' 替换为 "x265 --y4m --crf 21 --output output.hevc input.y4m" ，它应该按时间顺序输出以下行：

y4m  [info]: 1920x1080 fps 24000/1001 i420p10 frames 0 - 100 of 101
x265 [info]: Using preset ultrafast & tune none
raw  [info]: output file: C:\temp\output.hevc
x265 [info]: Main 10 profile, Level-4 (Main tier)
x265 [info]: Thread pool created using 16 threads
x265 [info]: Slices                              : 1
x265 [info]: frame threads / pool features       : 4 / wpp(34 rows)
x265 [info]: Coding QT: max CU size, min CU size : 32 / 16
x265 [info]: Residual QT: max TU size, max depth : 32 / 1 inter / 1 intra
x265 [info]: ME / range / subpel / merge         : dia / 57 / 0 / 2
x265 [info]: Keyframe min / max / scenecut / bias: 23 / 250 / 0 / 5.00
x265 [info]: Lookahead / bframes / badapt        : 5 / 3 / 0
x265 [info]: AQ: mode / str / qg-size / cu-tree  : 1 / 0.0 / 32 / 1
x265 [info]: Rate Control / qCompress            : CRF-21.0 / 0.60
x265 [info]: tools: strong-intra-smoothing lslices=6 deblock

[1.0%] 1/101 frames, 6.289 fps, 7217.8 kb/s
[25.7%] 26/101 frames, 59.23 fps, 299.23 kb/s
[45.5%] 46/101 frames, 66.76 fps, 322.81 kb/s  
[69.3%] 70/101 frames, 73.30 fps, 224.53 kb/s
[93.1%] 94/101 frames, 77.05 fps, 173.67 kb/s   

x265 [info]: frame I:      1, Avg QP:23.45  kb/s: 7098.44 
x265 [info]: frame P:     25, Avg QP:25.71  kb/s: 311.24  
x265 [info]: frame B:     75, Avg QP:28.33  kb/s: 23.89   
x265 [info]: consecutive B-frames: 3.8% 0.0% 0.0% 96.2% 

encoded 101 frames in 1.22s (82.58 fps), 165.06 kb/s, Avg QP:27.64

但事实是，中间部分的那些指示实时进度的输出块不会在每次更新时都被捕获。 popen.stdout.readline() 命令将被阻塞，直到进度达到 100%，然后完全输出。显然这不是我想要的。

(↓我指的是这部分)

[1.0%] 1/101 frames, 6.289 fps, 7217.8 kb/s
[25.7%] 26/101 frames, 59.23 fps, 299.23 kb/s
[45.5%] 46/101 frames, 66.76 fps, 322.81 kb/s  
[69.3%] 70/101 frames, 73.30 fps, 224.53 kb/s
[93.1%] 94/101 frames, 77.05 fps, 173.67 kb/s

谁能帮我弄清楚发生了什么以及如何解决它以实现我的目标？

非常感谢。

Answer 1

我的猜测是，由于命令输出是就地更新文本，因此末尾没有换行符，相反，输出只有一个回车 return 到 return 光标在同一行的开头并覆盖上一行。所以使用 readline 不会达到你想要的效果。您将必须编写自己的自定义逻辑来读取输出并将输出拆分为多行。

以下是我的实现

import re
import subprocess

cmd = r'ping www.baidu.com -n 4'
popen = subprocess.Popen(cmd, stdout = subprocess.PIPE ,stderr=subprocess.STDOUT ,shell=True)

read_chunk_size = 20
next_lines = ['']
while True:
    # read the stdout upto read_chunk_size bytes
    chunk = popen.stdout.read(read_chunk_size)
    # checking if process has finished
    if not chunk and popen.poll() != None:
        break
    # splitting the read string of charachters by either \n, \r or \n\r
    split_chunk = re.split('\n|\r|\n\r', chunk.decode('utf-8'))
    # combining the first of the split strings to the last of the strings
    # which were read in the last iteration. since we are reading upto only 
    # a fixed length, we may get incomplete lines
    next_lines = [next_lines[-1] + split_chunk[0]] + split_chunk[1:]
    # iterate upto the second last item in next_lines, since the last item may
    # still be incomplete which will be read in the next iteration
    for line in next_lines[:-1]:
        # read your lines here
        print(line)

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