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• Why is ffmpeg transcoding speed going down over time ?

  24 mars 2021, par Nikola R.

  I'm executing basic ffmpeg command to transcode input MP4 video to output MP4 video (both using H264 as video codec, and stripping out audio, for simplicity) :

  



  ffmpeg -i input-video.mp4 -b:v 20000k -an -vcodec libx264 output-video.mp4


  



  Transcoding is initially pretty fast (around 60-70 fps for first 20 or so frames), and then starts dropping steadily, ending at around 30 fps after 5000 frames.

  



  Is this inherent behavior ? If so, why does it happen ?
Also, is there any better option for the command line that would improve speed (besides using -threads) ?

  



  Would it be better to cut the input video and process it as smaller chunks, getting overall higher speed per sequence ? (I'm afraid that chunking might affect encoder's RD optimization)

  


• When passing arguments with php shell script eval isn't properly executing the script

  19 décembre 2017, par Aleksandra Lozanovska

  This is the part of my php script :

  $result ='ffmpeg -re -i /home/neotel/sample.mp4 -s 320x240 -vf setdar=4:3 -r 
  
  25 -c:v libx264 -b:v 2500k -c:a aac -b:a 128k -f mpegts 
  
  udp://192.168.88.211:5000' 
  
  $FILE1 = escapeshellarg($result);
  
  $output = shell_exec("sh testpetar.sh $FILE1 2>&1");

  This is my shell script :

  #!/usr/bin/env bash
  
  FILE1=$1
  
  FILE2="nohup "
  
  FILE3=" > log.txt"
  
  FILE="$FILE2$FILE1$FILE3"
  
  eval $FILE

  I am trying to pass the $results strings as the $FILE1 argument and then concatenate it with the strings $FILE2 and $FILE3 to form a whole ffmpeg command and execute it as a script in shell. When i execute it manually through Putty it is working properly, but when i am passing the $results command from php the eval function is not working.

• Ffmpeg hangs while transcoding HDHomerun Prime on channel change

  23 octobre 2017, par devo1929

  I’m using ffmpeg to transcode a live stream from a HDHomerun Prime. Everything is working beautifully. However, one ability that I would like, if possible, is the ability to change the channel on the HDHomerun without having to stop and restart the ffmpeg transcoding process.

  I start the ffmpeg process to begin reading the UDP feed from the HDHomerun. It writes the stream to a series of *.ts files with a m3u8 playlist.

  The second I use hdhomerun_config to change the channel on the device, ffmpeg immediately reports the following and hangs :

  [mpegts @ 0000018b4e05be60] New video stream 0:3 at pos:295211888 and DTS:40884.7s=108 drop=0 speed=1.02x
[mpegts @ 0000018b4e05be60] New audio stream 0:5 at pos:295279568 and DTS:40884.4s
frame= 4488 fps= 29 q=23.0 q=27.0 q=23.0 size=N/A time=00:02:28.94 bitrate=N/A dup=108 drop=0 speed=0.959x

  The command I am using to launch ffmpeg is :

  ffmpeg.exe -t 03:00:00 -i "udp://192.168.1.150:5000?fifo_size=1000000&overrun_nonfatal=1" -vf yadif=0:-1:1 -y -threads 4 -c:v libx264 -s 1280x720 -r 30 -b:v 4500k -force_key_frames expr:gte(t,n_forced*2) -profile:v high -preset fast -x264opts level=41 -c:a libfdk_aac -b:a 96k -ac 2 -hls_time 10 -hls_list_size 6 -hls_wrap 6 -hls_base_url /stream/ -hls_flags temp_file -hls_playlist_type event "C:\temp\streams\4500-stream.m3u8"

  Is there a specific command that I can pass to allow ffmpeg to "recover" from this ? Or, is there an arg that prevents this hang in the first place ? I’m using the latest version v3.4 of ffmpeg cross-compiled for Windows from Ubuntu. The issue also occurred using the stable version v3.4 of ffmpeg for Windows from ffmpeg.org.

  Edit :

  A new discovery to the issue, but still not yet resolved :
  If I change to the channel BACK to the original channel, Ffmpeg is able to continue writing the stream.

  Example : I start on channel X. Ffmpeg is recording to a file. I change to channel Y. Ffmpeg outputs a message similar to the one posted above and "hangs." I change back to channel X and ffmpeg picks up where it left off, no problem.