Filter Graph

Building filter graph is the most complicated part of fffw library. Let’s see how different parts work together to build this graph.

ff = FFMPEG()

Input streams

video = Stream(VIDEO)
audio = Stream(AUDIO)
source = Input(input_file='input.mp4', streams=(video, audio))
ff < source # ff.add_input(source)

In this example we use “stdin redirection operator” (<) to add new input file to FFMPEG instance. We could call FFMPEG.add_input if short variant is not appropriate.

Connect to filters

scale = ff.video | Crop(w=1920, h=1080) | Scale(1280, 720)

FFMPEG.video returns first available video stream across all inputs connected to FFMPEG that is not yet connected to filter graph. “Pipe” operator connects an input stream (or a filter) to first available input of next filter.

• If you need to point specific input stream, you may do it like:

  vol = Volume(20)
  source | vol  # source.audio.connect_dest(vol)
  

• Pipelines are useful if a stream is processed with long filter chain

• When a filter has multiple inputs, it can be used more than once as an argument for connect_dest:

  overlay = Overlay(x=100, y=100)
  main_video_stream | overlay
  logo_video_stream | overlay
  

• When a filter has multiple outputs, it can be connected to multiple filters:

  split = video | Split(VIDEO, output_count=3)
  split | Scale(1280, 720)
  split | Scale(960, 540)
  split | Scale(640, 360)
  

Note

each Stream can be used in filter graph only once, so use Split filter to reuse same input stream.

Output to codecs

Each stream in filter graph must be connected to an output codec. This is done via “stdout redirection operator”:

video_codec = VideoCodec('libx264')
audio_codec = AudioCodec('libfdk_aac')
output = Output(output_file='output.mp4',
                codecs=[video_codec, audio_codec])

overlay > video_codec

• Each codec consumes single stream from filter graph or from input file

• Free codec in output file is mapped automatically to a first available input stream of same kind. This can be changed by connecting input stream directly to a codec:

  ff.audio > audio_codec
  

• An input stream can be connected to multiple codecs (i.e. in different output files).

• Input stream can be used in filter graph only once (use Split filter to handle that).

Write files

To write any output file you must connect it to ffmpeg as an output using “stdout redirection operator”:

ff > output  # ff.add_output(output)

Note

Connecting Output to FFMPEG is obligatorily; without that no output file arguments will be generated.