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• FFMPEG Seeking with concat demuxer causes video & audio to be out of sync

  20 février 2023, par Garuuk

  I have a very simple use case that's driving me bananas.

  


  My problem and question :

  


  I'm using ffmpeg version 5.1.2 on a MacOS and i'm using ffmpeg seeking and concat demuxer to cut many 1 minute videos into 15 seconds chopped up over 12 clips where every clip is just 2 seconds from the same video (kind of like a mini teasers for the video). I would really like to not have to re-encode to make the video processing as fast as possible.

  


  First, I take each 1 minute video and cut it up into 12 clips (I do all this programmatically in python fwiw)

  


  ffmpeg -ss 0 -i input.mp4 -t 2 -c copy -y cut_1.mp4
ffmpeg -ss 4 -i input.mp4 -t 2 -c copy -y cut_2.mp4
ffmpeg -ss 8 -i input.mp4 -t 2 -c copy -y cut_3.mp4
...
...


  


  I then write all the output file names to my concat_manifest.txt

  


  file cut_1.mp4
file cut_2.mp4
...
...


  


  Then I run my concat command :

  


  ffmpeg -f concat -i concat_manifest.txt -c copy -y concat_video.mp4


  


  This works really fast but the audio and video at the stitch point get out of sync and sometimes the video just chokes & lags. It's mostly not a smooth experience.

  


  What I have tried :

  


  

  1. using the concat protocol with intermediate profiles : ffmpeg.org/wiki/Concatenate#demuxer

  


  2. Putting the -ss when I seek after the -i. This makes everything worse

  


  3. Playing around with different -ss values. This has some noticeable affects but it's not obvious why yet.

  


  4. I've also read from the ffmpeg resource regarding seeking and copying :

  


  


  Which leads me to believe that maybe because ffmpeg is using timestamps instead of frames, seeking isn't accurate using -ss when using the concat demuxer

  


  Is there a way to get concat demuxer cutting and concatenating the video where the audio is somewhat in sync with the video ?

  


  Thanks

  


  EDIT : I found an answer and i'll be posting the solution in the coming few days.

  


• Having trouble building FFmpeg using GNU make, Makefile:182 : /tests/Makefile : No such file or directory

  24 mai 2022, par Daedalus

  I'm having trouble building FFmpeg as a library to use in a project in vscode C++. I have no experience working with C/C++ libraries and would greatly appreciate any help. I've installed chocolatey and GNU make (GNU Make 4.3) with that, and the source code for FFmpeg. I cannot run make, as it tells me to do in the INSTALL.md file of the source code. I've been using command prompt to run the commands. Here are my errors :

  


  C:\ffmpeg>PowerShell ./configure

C:\ffmpeg>make
Makefile:182: /tests/Makefile: No such file or directory
make: *** No rule to make target '/tests/Makefile'.  Stop.

C:\ffmpeg>make install
Makefile:182: /tests/Makefile: No such file or directory
make: *** No rule to make target '/tests/Makefile'.  Stop.


  


  I've installed FFmpeg from github, and I can't find a working prebuilt library. I've tried different variations of the commands, with PowerShell and directories, but nothing has worked. This is INSTALL.md :

  


  


  Installing FFmpeg

  


  


  1. Type ./configure to create the configuration. A list of configure options is printed by running configure --help.

     


     configure can be launched from a directory different from the FFmpeg sources to build the objects out of tree. To do this, use an
absolute path when launching configure, e.g.
/ffmpegdir/ffmpeg/configure.

     


  


  2. Then type make to build FFmpeg. GNU Make 3.81 or later is required.

     


  


  3. Type make install to install all binaries and libraries you built.

     


  


  


  NOTICE

  


  

  • Non system dependencies (e.g. libx264, libvpx) are disabled by default.

  


  


  


  Any help would be greatly appreciated. Thanks in advance.

  


• Live jpeg sequence image to RTMP fps drop

  6 avril 2021, par m0j1

  I want to encode a sequence of jpg images (captured from my camera in unity) to h264 codec live stream video. I'm using the following command in ffmpeg :

  


  -f image2pipe -vcodec mjpeg -r 25 -i  udp://127.0.0.1:6000  -r 25 -preset slow -vcodec libx264 -tune zerolatency -b:v 800k -maxrate 800k -bufsize 400k  -f mpegts udp://127.0.0.1:5701


  


  On the other side, I playback this live stream using ffplay (ffplay -fflags nobuffer -flags low_delay -framedrop udp ://192.168.189.112:5701) and everything seems to be fine.
  
After that, I want to use a media server to restream this to other clients so I chose node media server and with the following ffmpeg comment I stream my image sequence to my media server :

  


  -f image2pipe -vcodec mjpeg -r 25 -i  udp://127.0.0.1:6000  -r 25 -preset slow -vcodec libx264 -tune zerolatency -b:v 800k -maxrate 800k -bufsize 400k  -f flv rtmp://192.168.189.112/live/STREAM_NAME


  


  But when I use ffplay to playback this live stream using the following command I get a choppy stream that looks like it is in 5fps :

  


  ffplay -fflags nobuffer -flags low_delay -framedroprtmp://192.168.189.112/live/STREAM_NAME

 


  


  I also tried to first record my live stream using node media server and then play it to see if I had received the data right and surprisingly the recorded video is perfect.

  
I wanted to ask if someone has any tips or experience about this.