Accessing Video Files as Python Sequences

Quite often I find myself writing scripts which need to load a few frames from a video file, process them and save the result to disk. It's a pain to implement video opening, seeking and decoding over and over again and complex Python bindings are a little overkill for my needs.

Videosequence is a library which hides the complexity of simply opening a video file in Python as a sequence of images. It exposes a video file as just that: a Python sequence type containing PIL Image-s.

For example, suppose you want to dump every frame from a video stored in foo.mp4 starting from frame 100:

from contextlib import closing
from videosequence import VideoSequence

with closing(VideoSequence("foo.mp4")) as frames:
    for idx, frame in enumerate(frames[100:]):
        frame.save("frame{:04d}.jpg".format(idx))

You can load a single frame from a sequence just as easily. Let's dump the final frame to another JPEG:

from contextlib import closing
from videosequence import VideoSequence

with closing(VideoSequence("foo.mp4")) as frames:
    frames[-1].save("final-frame.jpg")

In general, the VideoSequence behaves as if it were a long list of each frame in the video.

What VideoSequence does

• Frame-accurate seeking
• Single frame indexing (vs[0], vs[-4], etc.)
• Querying the length of the video (len(vs))
• Slicing a sequence of frames (vs[100:], vs[-20:], vs[10:20], vs[::2], etc.)
• Frames are represented as RGB PIL Image objects.
• Can interoperate with numpy. E.g. np.asarray(vs[0]).

What VideoSequence does not

• Handle files without exactly one (and only one) video stream
• Audio

Caveats

• Iterating forward one frame at a time is fast. Tricks such as iterating backwards or skipping n frames at a time work but is likely to be slow.
• The implementation is based on GStreamer and so de facto only works on a modern Unix-alike such as Linux or FreeBSD.
• The PyGObject introspection libraries must be installed. (See below.)

Installing

See the sections below for any OS-specific instructions. VideoSequence can be installed from the PyPI:

$ pip install --user videosequence

It can also be installed directly from git:

$ pip install --user git+git://github.com/rjw57/videosequence

Ubuntu and Debian

To install the Python GObject bindings:

$ sudo apt install gir1.2-gstreamer-1.0 gir1.2-gst-plugins-base-1.0 \
                   python-gi python3-gi

GStreamer is almost certainly already installed if you've got some modern desktop environment. If not:

$ sudo apt install libgstreamer1.0-dev gstreamer1.0-plugins-good

Contributing

Bug fixes and ports to new backends welcome. Please make sure that the tests still pass via tox before opening a new pull request. New functionality should come with tests, please.

Copyright and licensing

Videosequence is © 2016 Rich Wareham. Full licence details can be found in the LICENCE.txt file.