Concatenating transformations

When applying multiple transformations to a video, it is best to concatenate them on a Frames object:

>>> import birdwatcher as bw
>>> vfs = bw.VideoFileStream('myvideo.mp4')
>>> (vfs.iter_frames()
...    .resize((640,360))
...    .togray()
...    .blur(ksize=(5,5))
...    .draw_framenumbers()
...    .tovideo('myvideo_resized', framerate=vfs.avgframerate))

The 1) decodes the video (iter_frames), 2) resizes the video (resize) , 3) converts color to gray values (togray), 4) blurs frame images (blur), 5) draws frame numbers on frames (draw_framenumbers), and 6) encodes and saves the video (tovideo).

Concatenation avoids repeated decoding and encoding a video, which is computationally intensive. Also, multiple decoding-transformation-re-encoding rounds would lead to more loss of information as most video codecs apply lossy compression.