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• FFmpeg : About filter_complex command [closed]

  18 juin, par HJ Kim

  I use this command.

  ffmpeg -i Input.mp4 -i logo.png -c:v h264_nvenc -filter_complex "[0:v]scale=-1:720[video];[1:v][video]scale2ref=(iw/ih)*ih/8/sar:ih/8[wm][base];[base][wm]overlay=10:10" output.mp4

  But what does this mean?

  scale2ref=(iw/ih)*ih/8/sar:ih/8

• Using FFmpeg in .net ?

  17 juin, par daniel

  So I know its a fairly big challenge but I want to write a basic movie player/converter in c# using the FFmpeg library. However, the first obstacle I need to overcome is wrapping the FFmpeg library in c#. I've downloaded ffmpeg but couldn't compile it on Windows, so I downloaded a precompiled version for me. Ok awesome. Then I started looking for C# wrappers.

  I have looked around and have found a few wrappers such as SharpFFmpeg (http://sourceforge.net/projects/sharpffmpeg/) and ffmpeg-sharp (http://code.google.com/p/ffmpeg-sharp/). First of all, I wanted to use ffmpeg-sharp as its LGPL and SharpFFmpeg is GPL. However, it had quite a few compile errors. Turns out it was written for the mono compiler, I tried compiling it with mono but couldn't figure out how. I then started to manually fix the compiler errors myself, but came across a few scary ones and thought I'd better leave those alone. So I gave up on ffmpeg-sharp.

  Then I looked at SharpFFmpeg and it looks like what I want, all the functions P/Invoked for me. However its GPL? Both the AVCodec.cs and AVFormat.cs files look like ports of avcodec.c and avformat.c which I reckon I could port myself? Then not have to worry about licencing.

  But I want to get this right before I go ahead and start coding. Should I:

  1. Write my own C++ library for interacting with ffmpeg, then have my C# program talk to the C++ library in order to play/convert videos etc.

  OR

  2. Port avcodec.h and avformat.h (is that all i need?) to c# by using a whole lot of DllImports and write it entirely in C#?

  First of all consider that I'm not great at C++ as I rarely use it but I know enough to get around. The reason I'm thinking #1 might be the better option is that most FFmpeg tutorials are in C++ and I'd also have more control over memory management than if I was to do it in c#.

  What do you think? Also would you happen to have any useful links (perhaps a tutorial) for using FFmpeg?

• Text on video ffmpeg

  17 juin, par Jesper Madsen

  How can I add text overlay on my video in ffmpeg?

  i.e. given a video "video1.flv", how can I add "StackOverflow" text during the whole video, positioned in the middle of the screen, with white text and a border?

• Writing a video frame by frame using ffmpeg

  16 juin, par Chris

  I am trying to write a video frame-by-frame using ffmpeg as explained here: http://zulko.github.io/blog/2013/09/27/read-and-write-video-frames-in-python-using-ffmpeg/

  However, I am always getting an OSError: [Errno 22] Invalid argument. I am on Windows 7 and using Python 3.4.

  Here is the code:

  import subprocess as sp
  import numpy as np
  import time
  
  ffmpeg_bin = r'C:\path\to\ffmpeg\ffmpeg.exe'
  
  command = [ffmpeg_bin,
             '-y', # (optional) overwrite output file if it exists
             '-f', 'rawvideo',
             '-vcodec','rawvideo',
             '-s', '420x360', # size of one frame
             '-pix_fmt', 'rgb24',
             '-r', '24', # frames per second
             '-i', '-', # The imput comes from a pipe
             '-an', # Tells FFMPEG not to expect any audio
             '-vcodec', 'mpeg',
             'my_output_videofile.mp4' ]
  
  proc = sp.Popen(command, stdin=sp.PIPE, stderr=sp.PIPE)
  
  a = np.zeros((360, 420, 3), dtype=np.uint8)
  
  for ii in range(5*24):
      print(ii)
      proc.stdin.write(a.tostring())
      time.sleep(1/24)
  
  proc.stdin.close()
  proc.stderr.close()
  proc.wait()
  

  And here is the output of the program:

  0
  1
  Traceback (most recent call last):
    File ".\write_dummy_video.py", line 25, in 
      proc.stdin.write(a.tostring())
  OSError: [Errno 22] Invalid argument
  

  Interestingly, if I comment line number 26 (i.e. time.sleep(1/24)) the error message changes slightly but the loop still only runs twice. Here is the error output:

  0
  1
  Traceback (most recent call last):
    File ".\write_dummy_video.py", line 25, in 
      proc.stdin.write(a.tostring())
  BrokenPipeError: [Errno 32] Broken pipe
  

  What could be causing this problem, and how can I fix it?

• How can I convert audio to WAVE_FORMAT_PCM using FFmpeg ?

  16 juin, par Eric Stdlib

  I am using Python's wave module to read audio, and using FFmpeg to convert audio from other types to wav. However, I am encountering some problem.

  I wrote v.py to generate an silence audio file a.wav

  import sys, wave, math
  import numpy as np
  
  wave_data = np.zeros(44100).astype(np.short)
  
  f = wave.open('a.wav', 'wb')
  f.setnchannels(1)
  f.setsampwidth(2)
  f.setframerate(96000)
  f.writeframes(wave_data.tostring())
  f.close()
  

  Then I used FFmpeg to "copy" a.wav to b.wav (though it seems to encode / decode the file), but I can only read a.wav with Python; b.wav cannot be opened.

  [user@localhost tmp]$ ffmpeg -i a.wav b.wav
  Guessed Channel Layout for Input Stream #0.0 : mono
  Input #0, wav, from 'a.wav':
    Duration: 00:00:00.46, bitrate: 1536 kb/s
      Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 96000 Hz, mono, s16, 1536 kb/s
  Stream mapping:
    Stream #0:0 -> #0:0 (pcm_s16le (native) -> pcm_s16le (native))
  Press [q] to stop, [?] for help
  Output #0, wav, to 'b.wav':
    Metadata:
      ISFT            : Lavf57.71.100
      Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 96000 Hz, mono, s16, 1536 kb/s
      Metadata:
        encoder         : Lavc57.89.100 pcm_s16le
  size=      86kB time=00:00:00.45 bitrate=1537.8kbits/s speed= 706x    
  video:0kB audio:86kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.115646%
  [user@localhost tmp]$ python3
  Python 3.6.4 (default, Jan 23 2018, 22:25:37) 
  [GCC 7.2.1 20170915 (Red Hat 7.2.1-2)] on linux
  Type "help", "copyright", "credits" or "license" for more information.
  >>> import wave
  >>> wave.open('a.wav')
  
  >>> wave.open('b.wav')
  Traceback (most recent call last):
    File "", line 1, in 
    File "/usr/lib64/python3.6/wave.py", line 499, in open
      return Wave_read(f)
    File "/usr/lib64/python3.6/wave.py", line 163, in __init__
      self.initfp(f)
    File "/usr/lib64/python3.6/wave.py", line 143, in initfp
      self._read_fmt_chunk(chunk)
    File "/usr/lib64/python3.6/wave.py", line 260, in _read_fmt_chunk
      raise Error('unknown format: %r' % (wFormatTag,))
  wave.Error: unknown format: 65534
  >>> 
  

  How should I change the command of FFmpeg to convert the file to WAVE_FORMAT_PCM, so that I can read b.wav with Python?