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• ffmpeg : md5 of m3u8 playlists generated from same input video with different segment durations (after applying video filter) don't match

  15 juillet 2020, par Saurabh P Bhandari

  Here are a few commands I am using to convert and transize a video in mp4 format to a m3u8 playlist.

  


  For a given input video (mp4 format), generate multiple video only segments with segment duration 30s

  


  ffmpeg -loglevel error -i input.mp4 -dn -sn -an -c:v copy -bsf:v h264_mp4toannexb -copyts -start_at_zero -f segment -segment_time 30 30%03d.mp4 -dn -sn -vn -c:a copy audio.aac


  


  Apply video filter (in this case scaling) on each segment and convert it to a m3u8 format

  


  ls 30*.mp4 | parallel 'ffmpeg -loglevel error -i {} -vf scale=-2:144 -hls_list_size 0 {}.m3u8'


  


  Store the list of m3u8 files generated in list.txt in this format file 'segment-name.m3u8'

  


  for f in 30*.m3u8; do echo "file '$f'" >> list.txt; done


  


  Using concat demuxer, combine all segment files (which are in m3u8 format) and the audio to get one final m3u8 playlist pointing to segments with duration of 10s.

  


  ffmpeg -loglevel error -f concat -i list.txt -i audio.aac -c copy -hls_list_size 0 -hls_time 10 output_30.m3u8


  


  ---

  


  I can change the segment duration in the first step from 30s to 60s, and compare the md5 of the final m3u8 playlist generated in both the cases using this command

  


  ffmpeg -loglevel error -i <input m3u8="m3u8" playlist="playlist" /> -f md5 - &#xA;

  


  The md5 of the output files differ i.e video streams of output_30.m3u8 and output_60.m3u8 are not the same.

  


  Can anyone elaborate on this ?

  


  (I expected the md5 to be the same)

  


• subprocess called from multiprocess not finishing

  24 juin 2020, par Pavel Komarov

  I've got a set of videos from which I'm trying to pull random frames. There are a lot of videos, so I want to work in parallel, and ffmpeg can splice out the frames for me, so here's the important part of the code :

  


  import os
from tqdm import tqdm
from joblib import Parallel, delayed
from multiprocessing import current_process
from subprocess import Popen

vids_dir = 'just a string'
out_dir = 'another string'

def process_each(f):
    temp = 'temp' + str(current_process()._identity[0])
    os.mkdir(temp)

    proc = Popen(['ffmpeg -i ' + vids_dir + '/' + f + ' ' + temp + '/' + f[:-4] + '_%03d.jpg &> /dev/null'], shell=True) # convert to frames
    proc.wait()

    # do stuff

    os.system('rm -rf ' + temp) # clean up


Parallel(n_jobs=10)(delayed(process_each)(f) for f in tqdm(os.listdir(vids_dir)))


  


  I can print out the command being passed to Popen and execute it in a shell, and it works. I can open a python3 session and call the command from Popen or subprocess.call or even os.system, and it works. I can even set n_jobs=1 in my Parallel, and it works.

  


  But the moment I actually parallelize this, I find ffmpeg doesn't flush its full results to the temporary folders ; it only gets the first one or few frames.

  


  What on earth could be going on ? subprocess and multiprocessing should be able to mix this way.

  


• Transcode HLS segments individually with FFMPEG

  9 juillet 2020, par Mathix420

  I'm trying to transcode a video in HLS, by first splitting the video in segments without encoding changes and then transcode all segments individually. I'm trying to achieve this so I can transcode a video in multiple EC2 instances in parallel to be more time efficient.

  


  I am using this scipt right now

  


  # Split input file in multiple segments

ffmpeg -hide_banner -y -i $input -c copy -map 0 -an -segment_time 4 -reset_timestamps 1 -f segment output%03d.webm

# Transcode each segments in multiple resolutions

find . -name 'output*.webm' -exec ffmpeg -hide_banner -y -i {} \
  -vf "scale=-2:360" -c:v libx264 -profile:v main -crf 20 -sc_threshold 0 -b:v 800k -maxrate 856k -bufsize 1200k {}.360p.ts \
  -vf "scale=-2:480" -c:v libx264 -profile:v main -crf 20 -sc_threshold 0 -b:v 1400k -maxrate 1498k -bufsize 2100k {}.480p.ts \
  -vf "scale=-2:720" -c:v libx264 -profile:v main -crf 20 -sc_threshold 0 -b:v 2800k -maxrate 2996k -bufsize 4200k {}.720p.ts \
  -vf "scale=-2:1080" -c:v libx264 -profile:v main -crf 20 -sc_threshold 0 -b:v 5000k -maxrate 5350k -bufsize 7500k {}.1080p.ts \;


  


  But then when I tried to get all segments durations to make an m3u8 playlist (with the command below)

  


  # List segments duration

find . -name 'output*.webm.360p.ts' \
  -exec echo -n {} \; \
  -exec ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 {} \;


  


  I got this result

  


  output000.webm.360p.ts 5.120000
output001.webm.360p.ts 5.120000
output002.webm.360p.ts 4.400000
output003.webm.360p.ts 5.480000
output004.webm.360p.ts 0.360000
output005.webm.360p.ts 5.120000
output006.webm.360p.ts 4.960000
output007.webm.360p.ts 0.001000


  


  I can't figure out why my output004 is only 0.360000 seconds long.

  


  When I tried to play it with VLC it just shows one or two frames then main decoder error: buffer deadlock prevented.

  


  Thanks for trying to help me !