在循环中，我在python脚本中有此命令：
ffmpeg -i somefile.mp4 -ss 00:03:12 -t 00:00:35 piece.mp4 -loglevel error -stats
它剪切出输入文件（-i）的片段。输入的文件名以及开始时间（-ss）和我剪切的片段长度（-t）有所不同，因此它会读取mp4文件的数量，并从每个文件中剪切出一些片段。在脚本执行期间，它可能被调用约100次。我的问题是，每次开始之前，都会有6到15秒的延迟，并且这会花费大量时间。我怎样才能立即开始？
最初，我认为这是进程优先级的问题，但是我注意到，即使在“暂停”期间，所有处理器也都以100％的速度工作，因此显然正在完成某些工作。
脚本（process_videos.py）：
import subprocess
import sys
import math
import time
class TF:
"""TimeFormatter class (TF).
This class' reason for being is to convert time in short
form, e.g. 1:33, 0:32, or 23 into long form accepted by
mp4cut function in bash, e.g. 00:01:22, 00:00:32, etc"""
def toLong(self, shrt):
"""Converts time to its long form"""
sx = '00:00:00'
ladd = 8 - len(shrt)
n = sx[:ladd] + shrt
return n
def toShort(self, lng):
"""Converts time to short form"""
if lng[0] == '0' or lng[0] == ':':
return self.toShort(lng[1:])
else:
return lng
def toSeconds(self, any_time):
"""Converts time to seconds"""
if len(any_time) < 3:
return int(any_time)
tt = any_time.split(':')
if len(any_time) < 6:
return int(tt[0])*60 + int(tt[1])
return int(tt[0])*3600 + int(tt[1])*60 + int(tt[2])
def toTime(self, secsInt):
""""""
tStr = ''
hrs, mins, secs = 0, 0, 0
if secsInt >= 3600:
hrs = math.floor(secsInt / 3600)
secsInt = secsInt % 3600
if secsInt >= 60:
mins = math.floor(secsInt / 60)
secsInt = secsInt % 60
secs = secsInt
return str(hrs).zfill(2) + ':' + str(mins).zfill(2) + ':' + str(secs).zfill(2)
def minus(self, t_start, t_end):
""""""
t_e = self.toSeconds(t_end)
t_s = self.toSeconds(t_start)
t_r = t_e - t_s
hrs, mins, secs = 0, 0, 0
if t_r >= 3600:
hrs = math.floor(t_r / 3600)
t_r = t_r - (hrs * 3600)
if t_r >= 60:
mins = math.floor(t_r / 60)
t_r = t_r - (mins * 60)
secs = t_r
hrsf = str(hrs).zfill(2)
minsf = str(mins).zfill(2)
secsf = str(secs).zfill(2)
t_fnl = hrsf + ':' + minsf + ':' + secsf
return t_fnl
def go_main():
tf = TF()
vid_n = 0
arglen = len(sys.argv)
if arglen == 2:
with open(sys.argv[1], 'r') as f_in:
lines = f_in.readlines()
start = None
end = None
cnt = 0
for line in lines:
if line[:5] == 'BEGIN':
start = cnt
if line[:3] == 'END':
end = cnt
cnt += 1
if start == None or end == None:
print('Invalid file format. start = {}, end = {}'.format(start,end))
return
else:
lines_r = lines[start+1:end]
del lines
print('videos to process: {}'.format(len(lines_r)))
f_out_prefix = ""
for vid in lines_r:
vid_n += 1
print('\nProcessing video {}/{}'.format(vid_n, len(lines_r)))
f_out_prefix = 'v' + str(vid_n) + '-'
dat = vid.split('!')[1:3]
title = dat[0]
dat_t = dat[1].split(',')
v_pieces = len(dat_t)
piece_n = 0
video_pieces = []
cmd1 = "echo -n \"\" > tmpfile"
subprocess.run(cmd1, shell=True)
print(' new tmpfile created')
for v_times in dat_t:
piece_n += 1
f_out = f_out_prefix + str(piece_n) + '.mp4'
video_pieces.append(f_out)
print(' piece filename {} added to video_pieces list'.format(f_out))
v_times_spl = v_times.split('-')
v_times_start = v_times_spl[0]
v_times_end = v_times_spl[1]
t_st = tf.toLong(v_times_start)
t_dur = tf.toTime(tf.toSeconds(v_times_end) - tf.toSeconds(v_times_start))
cmd3 = ["ffmpeg", "-i", title, "-ss", t_st, "-t", t_dur, f_out, "-loglevel", "error", "-stats"]
print(' cutting out piece {}/{} - {}'.format(piece_n, len(dat_t), t_dur))
subprocess.run(cmd3)
for video_piece_name in video_pieces:
cmd4 = "echo \"file " + video_piece_name + "\" >> tmpfile"
subprocess.run(cmd4, shell=True)
print(' filename {} added to tmpfile'.format(video_piece_name))
vname = f_out_prefix[:-1] + ".mp4"
print(' name of joined file: {}'.format(vname))
cmd5 = "ffmpeg -f concat -safe 0 -i tmpfile -c copy joined.mp4 -loglevel error -stats"
to_be_joined = " ".join(video_pieces)
print(' joining...')
join_cmd = subprocess.Popen(cmd5, shell=True)
join_cmd.wait()
print(' joined!')
cmd6 = "mv joined.mp4 " + vname
rename_cmd = subprocess.Popen(cmd6, shell=True)
rename_cmd.wait()
print(' File joined.mp4 renamed to {}'.format(vname))
cmd7 = "rm " + to_be_joined
rm_cmd = subprocess.Popen(cmd7, shell=True)
rm_cmd.wait()
print('rm command completed - pieces removed')
cmd8 = "rm tmpfile"
subprocess.run(cmd8, shell=True)
print('tmpfile removed')
print('All done')
else:
print('Incorrect number of arguments')
############################
if __name__ == '__main__':
go_main()
process_videos.py：
$ python process_videos.py video_data
video_data文件具有以下格式：
BEGIN
!first_video.mp4!3-23,55-1:34,2:01-3:15,3:34-3:44!
!second_video.mp4!2-7,12-44,1:03-1:33!
END
我的系统详细信息：
System: Host: snowflake Kernel: 5.4.0-52-generic x86_64 bits: 64 Desktop: Gnome 3.28.4
Distro: Ubuntu 18.04.5 LTS
Machine: Device: desktop System: Gigabyte product: N/A serial: N/A
Mobo: Gigabyte model: Z77-D3H v: x.x serial: N/A BIOS: American Megatrends v: F14 date: 05/31/2012
CPU: Quad core Intel Core i5-3570 (-MCP-) cache: 6144 KB
clock speeds: max: 3800 MHz 1: 1601 MHz 2: 1601 MHz 3: 1601 MHz 4: 1602 MHz
Drives: HDD Total Size: 1060.2GB (55.2% used)
ID-1: /dev/sda model: ST31000524AS size: 1000.2GB
ID-2: /dev/sdb model: Corsair_Force_GT size: 60.0GB
Partition: ID-1: / size: 366G used: 282G (82%) fs: ext4 dev: /dev/sda1
ID-2: swap-1 size: 0.70GB used: 0.00GB (0%) fs: swap dev: /dev/sda5
Info: Processes: 313 Uptime: 16:37 Memory: 3421.4/15906.9MB Client: Shell (bash) inxi: 2.3.56
更新：
根据Charles'的建议，我使用了性能采样：
# perf record -a -g sleep 180
...这是报告：
Samples: 74K of event 'cycles', Event count (approx.): 1043554519767
Children Self Command Shared Object
- 50.56% 45.86% ffmpeg libavcodec.so.57.107.100
- 3.10% 0x4489480000002825
0.64% 0x7ffaf24b92f0
- 2.12% 0x5f7369007265646f
av_default_item_name
1.39% 0
- 44.48% 40.59% ffmpeg libx264.so.152
5.78% x264_add8x8_idct_avx2.skip_prologue
3.13% x264_add8x8_idct_avx2.skip_prologue
2.91% x264_add8x8_idct_avx2.skip_prologue
2.31% x264_add8x8_idct_avx.skip_prologue
2.03% 0
1.78% 0x1
1.26% x264_add8x8_idct_avx2.skip_prologue
1.09% x264_add8x8_idct_avx.skip_prologue
1.06% x264_me_search_ref
0.97% x264_add8x8_idct_avx.skip_prologue
0.60% x264_me_search_ref
- 38.01% 0.00% ffmpeg [unknown]
4.10% 0
- 3.49% 0x4489480000002825
0.70% 0x7ffaf24b92f0
0.56% 0x7f273ae822f0
0.50% 0x7f0c4768b2f0
- 2.29% 0x5f7369007265646f
av_default_item_name
1.99% 0x1
10.13% 10.12% ffmpeg [kernel.kallsyms]
- 3.14% 0.73% ffmpeg libavutil.so.55.78.100
2.34% av_default_item_name
- 1.73% 0.21% ffmpeg libpthread-2.27.so
- 0.70% pthread_cond_wait@@GLIBC_2.3.2
- 0.62% entry_SYSCALL_64_after_hwframe
- 0.62% do_syscall_64
- 0.57% __x64_sys_futex
0.52% do_futex
0.93% 0.89% ffmpeg libc-2.27.so
- 0.64% 0.64% swapper [kernel.kallsyms]
0.63% secondary_startup_64
0.21% 0.18% ffmpeg libavfilter.so.6.107.100
0.20% 0.11% ffmpeg libavformat.so.57.83.100
0.12% 0.11% ffmpeg ffmpeg
0.11% 0.00% gnome-terminal- [unknown]
0.09% 0.07% ffmpeg libm-2.27.so
0.08% 0.07% ffmpeg ld-2.27.so
0.04% 0.04% gnome-terminal- libglib-2.0.so.0.5600.4