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• How to stop perl buffering ffmpeg output

  4 février 2017, par Sebastian King

  I am trying to have a Perl program process the output of an ffmpeg encode, however my test program only seems to receive the output of ffmpeg in periodic chunks, thus I am assuming there is some sort of buffering going on. How can I make it process it in real-time ?

  My test program (the tr command is there because I thought maybe ffmpeg’s carriage returns were causing perl to see one big long line or something) :

  #!/usr/bin/perl
  
  
  
  $i = "test.mkv"; # big file, long encode time
  
  $o = "test.mp4";
  
  
  
  open(F, "-|", "ffmpeg -y -i '$i' '$o' 2>&1 | tr '\r' '\n'")
  
          or die "oh no";
  
  
  
  while(<f>) {
  
          print "A12345: $_"; # some random text so i know the output was processed in perl
  
  }
  
  </f>

  Everything works fine when I replace the ffmpeg command with this script :

  #!/bin/bash
  
  
  
  echo "hello";
  
  
  
  for i in `seq 1 10`; do
  
          sleep 1;
  
          echo "hello $i";
  
  done
  
  
  
  echo "bye";

  When using the above script I see the output each second as it happens. With ffmpeg it is some 5-10 seconds or so until it outputs and will output sometimes 100 lines each output.

  I have tried using the program unbuffer ahead of ffmpeg in the command call but it seems to have no effect. Is it perhaps the 2>&1 that might be buffering ?
  Any help is much appreciated.

  If you are unfamiliar with ffmpeg’s output, it outputs a bunch of file information and stuff to STDOUT and then during encoding it outputs lines like

  frame=  332 fps= 93 q=28.0 size=     528kB time=00:00:13.33 bitrate= 324.2kbits/s speed=3.75x

  which begin with carriage returns instead of new lines (hence tr) on STDERR (hence 2>&1).

• Problems with ffmpeg cross-compilation for windows x64 using linux/mingw

  3 mai 2023, par Adam

  I'm cross-compiling ffmpeg with NVIDIA hw acceleration for windows 64 with ubuntu/mingw.
The configuration/make process is OK but dumpbin shows that avfilter-9.dll file tries to import some kernel functions twice - from kernel32 which is correct and second time from... npp dlls !

  


  dumpbin /imports avfilter-9.dll
:
    nppig64_12.dll
             180587CC8 Import Address Table
             180587148 Import Name Table
                     0 time date stamp
                     0 Index of first forwarder reference

                         154 nppiRotate_8u_C1R
                         100 nppiResizeSqrPixel_8u_C1R
                           1 AcquireSRWLockExclusive
                         11B DeleteCriticalSection
                         13F EnterCriticalSection
                         228 GetCurrentProcess
                         229 GetCurrentProcessId
                         22D GetCurrentThreadId
                         276 GetLastError
:
   KERNEL32.dll
             180587CD8 Import Address Table
             180587158 Import Name Table
                     0 time date stamp
                     0 Index of first forwarder reference

                           1 AcquireSRWLockExclusive
                         11B DeleteCriticalSection
                         13F EnterCriticalSection
                         228 GetCurrentProcess
                         229 GetCurrentProcessId
                         22D GetCurrentThreadId
                         276 GetLastError
                         301 GetSystemTimeAsFileTime
                         31F GetTickCount
                         375 InitOnceBeginInitialize


  


  My ./configure :

  


  sudo PKG_CONFIG_PATH=/usr/local/lib/pkgconfig/ ./configure --arch=x86_64 --target-os=mingw64 --cross-prefix=x86_64-w64-mingw32- --enable-nonfree --enable-cuda-nvcc --enable-nvenc --enable-libnpp --extra-cflags=-I/usr/local/cuda/include --extra-ldflags=-L/usr/local/cuda/lib64 --extra-cflags=-I../npp_dev/include/ --extra-ldflags=-L../npp_dev/lib/x64/ --disable-static --enable-shared


  


  /npp_dev contains include/lib files for npp (windows 64).

  


  Anybody encountered similar issue or has any idea what I should start looking at ?

  


  Important note - without —enable-libnpp the avfilter-9.dll is correctly generated.

  


  Thanks ! //Adam

  


• ffmpeg - concatenate several videos with xfade transition

  8 mai 2021, par ilim

  I have N videos, and I'm using ffmpeg to concatenate them with xfade transitions between them. The video files are named as positive integers representing their order in the concatenated output, and none of them have any audio. In fact, each file just includes a different image with no animation that stays on screen all through that video's duration.

  


  I'm using a simple command I found in a response to an existing question to concatenate the first 2 videos :

  


  ffmpeg -i 1.mp4 -i 2.mp4 -y
       -filter_complex "xfade=transition=fade:offset=3.5:duration=0.5"
       1-2.mp4


  


  I planned to employ that same command for all the videos, each time appending a single video to the cumulative one produced so far, and producing an intermediary output to be used later.

  


  Specifically, I first concatenated files 1.mp4 and 2.mp4, and recorded the result into 1-2.mp4, which was produced correctly. Videos had the respective duration of 4 and 8 seconds, and the resulting 1-2.mp4 was 12 seconds long, with the transition occurring when it should.

  


  The problem started when I tried concatenating 1-2.mp4 and 3.mp4. I used the following command to generate a concatenation of videos [1-3].

  


  ffmpeg -i 1-2.mp4 -i 3.mp4 -y
       -filter_complex "xfade=transition=fade:offset=11.5:duration=0.5"
       1-3.mp4


  


  The video produced seems to be an exact copy of 1-2.mp4, and contents of 3.mp4 are not present at all in the resulting 1-3.mp4. Video file 3.mp4 was 3 seconds long, but the resulting 1-3.mp4 was 12 seconds long, just like 1-2.mp4 was.

  


  Apart from the input and output file names, both commands are the same. I was suspicious of having set the offset parameter of the transition incorrectly, but the first 2 files were merged successfully.

  


  I am at a loss as to what I'm doing incorrectly here. Is there a particular caveat of the xfade filter that gets problematic when used among 2 files with one of them already having that filter ?

  


  Any suggestions as to how I may debug or fix this behavior ? I'd welcome any alternative means of concatenating these (i.e., with some transition effects) in a simple fashion as well.

  


  I'm planning to use these commands in a Python script, so I'd appreciate any alternative solution not involving any gigantic commands or parameters.

  


  Just to be thorough, I should mention that I have ffmpeg version 4.3.1 installed via snap.