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• Compiling FFMPEG on CentOS DigitalOcean

  29 juillet 2015, par coder_uk

  I set up a DigitalOcean instance running CentOS 6.5 and successfully followed the guide to compile FFMPEG (https://trac.ffmpeg.org/wiki/CompilationGuide/Centos). Hurrah !

  But of course I realised that by default, DigitalOcean creates a root user and so ffmpeg now lives in /root/bin/ffmpeg. Which isn’t ideal because when I want to exec the ffmpeg bin from nginx, I would have to run nginx as root for it to have permission.

  Questions ...

  1) Long-shot, but presumably if I change the owner of the ffmpeg binary to nginx, it still won’t work, because nginx won’t be able to access the /root folder it is in. Correct ?

  2) I could run nginx as root (’user root’). But this seems like a very bad idea. Correct ?

  3) Which leaves me with the option of creating a new user, and then compiling ffmpeg into its home folder. But : which user ? EC2 creates ’ec2-user’, so should I make my own equivalent for DO ? But then won’t I have to run nginx as that user, else I’ll run into the same problem ?

  Or should I compile ffmpeg into the ’nginx’ home folder, if indeed it has one ? Is that how it is supposed to be done ?

  Since compiling ffmpeg takes ages, I don’t want to keep doing it, and the static files all seem very out of date. Thanks

• Feeding FFMPEG from buffer in c code RAW H264 to MP4 wrapping

  8 mai 2017, par abraxas1

  i have a raw h264 stream coming in from cameras with a custom API. data gets put into a callback function in my c code.

  i need to wrap this as mp4. i’m using ffmpeg to do this now, but only after the h264es file has been written and closed, so very time consuming on a beaglebone-like processor.

  i have been trying to write this data to a named pipe and feed that to ffmpeg but can not get this to work. maybe i’m not opening/closing pipes properly, it hangs. or not specifying the piping properly for ffmpeg.

  is it possible to feed the buffered data more directly to ffmpeg ?
  or, how do i set up the named pipe to work properly ?

  first i’m opening the fifo like this

  g_fifoname="/tmp/fifocam1.h264";
  
  mkfifo(g_fifoname, 0666);               // make the fifos
  
  fd_fifo[ch+brd*2] = open(g_fifoname, O_RDWR);

  then, i’m calling ffmpeg like this, at this moment anyway. trying many things.

  char* execargs[]={PATH_TO_FFMPEG,"-re","-y","-framerate","30","-f","h264","-video_size","1920x1080","-i",g_fifname,"-c:v","copy","-an",pathname, (char*)0};

  i probably got the ffmpeg call wrong. argh.
  i open the fifo first, then start ffmpeg.
  when streaming is stopped i close fifo’s, then close ffmpeg output file.

  ffmpeg is so powerful and frustrating to wrangle.
  thanks all,

• How to remove a frame with ffmpeg without re-encoding ?

  3 juin 2022, par jonahclarsen

  I am making a datamoshing program in C++, and I need to find a way to remove one frame from a video (specifically, the p-frame right after a sequence jump) without re-encoding the video. I am currently using h.264 but would like to be able to do this with VP9 and AV1 as well.

  


  I have one way of going about it, but it doesn't work for one frustrating reason (mentioned later). I can turn the original video into two intermediate videos - one with just the i-frame before the sequence jump, and one with the p-frame that was two frames later. I then create a concat.txt file with the following contents :

  


  file video.mkv
file video1.mkv


  


  And run ffmpeg -y -f concat -i concat.txt -c copy output.mp4. This produces the expected output, although is of course not as efficient as I would like since it requires creating intermediate files and reading the .txt file from disk (performance is very important in this project).

  


  But worse yet, I couldn't generate the intermediate videos with ffmpeg, I had to use avidemux. I tried all sorts of variations on ffmpeg -y -ss 00:00:00 -i video.mp4 -t 0.04 -codec copy video.mkv, but that command seems to really bug out with videos of length 1-2 frames - while it works for longer videos no problem. My best guess is that there is some internal checker to ensure the output video is not corrupt (which, unfortunately, is exactly what I want it to be !).

  


  Maybe there's a way to do it this way that gets around that problem, or better yet, a more elegant solution to the problem in the first place.

  


  Thanks !