turdusmerula / v4l2py

V4L2 python library

v4l2py

Video for linux 2 (V4L2) python library

A two purpose API:

• high level Device API for humans to play with :-)
• raw python binding for the v4l2 (video4linux2) userspace API, using ctypes (don't even bother wasting your time here. You probably won't use it)

Only works on python >= 3.7.

Installation

From within your favorite python environment:

$ pip install v4l2py

Usage

Without further ado:

>>> from v4l2py import Device
>>> with Device.from_id(0) as cam:
>>>     for i, frame in enumerate(cam):
...         print(f"frame #{i}: {len(frame)} bytes")
...         if i > 9:
...             break
...
frame #0: 54630 bytes
frame #1: 50184 bytes
frame #2: 44054 bytes
frame #3: 42822 bytes
frame #4: 42116 bytes
frame #5: 41868 bytes
frame #6: 41322 bytes
frame #7: 40896 bytes
frame #8: 40844 bytes
frame #9: 40714 bytes
frame #10: 40662 bytes

Getting information about the device:

>>> from v4l2py.device import Device, BufferType

>>> cam = Device.from_id(0)
>>> cam.open()
>>> cam.info.card
'Integrated_Webcam_HD: Integrate'

>>> cam.info.capabilities
<Capability.STREAMING|EXT_PIX_FORMAT|VIDEO_CAPTURE: 69206017>

>>> cam.info.formats
[ImageFormat(type=<BufferType.VIDEO_CAPTURE: 1>, description=b'Motion-JPEG',
             flags=<ImageFormatFlag.COMPRESSED: 1>, pixelformat=<PixelFormat.MJPEG: 1196444237>),
 ImageFormat(type=<BufferType.VIDEO_CAPTURE: 1>, description=b'YUYV 4:2:2',
             flags=<ImageFormatFlag.0: 0>, pixelformat=<PixelFormat.YUYV: 1448695129>)]

>>> cam.get_format(BufferType.VIDEO_CAPTURE)
Format(width=640, height=480, pixelformat=<PixelFormat.MJPEG: 1196444237>}

>>> for ctrl in cam.controls.values(): print(ctrl)
<Control brightness type=integer min=0 max=255 step=1 default=128 value=64>
<Control contrast type=integer min=0 max=255 step=1 default=32 value=32>
<Control saturation type=integer min=0 max=100 step=1 default=64 value=64>
<Control hue type=integer min=-180 max=180 step=1 default=0 value=0>
<Control white_balance_automatic type=boolean default=1 value=1>
<Control gamma type=integer min=90 max=150 step=1 default=120 value=120>
<Control gain type=integer min=1 max=7 step=1 default=1 value=1>
<Control power_line_frequency type=menu min=0 max=2 step=1 default=2 value=2>
<Control white_balance_temperature type=integer min=2800 max=6500 step=1 default=4000 value=4000 flags=inactive>
<Control sharpness type=integer min=0 max=7 step=1 default=2 value=2>
<Control backlight_compensation type=integer min=0 max=1 step=1 default=0 value=0>
<Control auto_exposure type=menu min=0 max=3 step=1 default=3 value=3>
<Control exposure_time_absolute type=integer min=10 max=333 step=1 default=156 value=156 flags=inactive>
<Control exposure_dynamic_framerate type=boolean default=0 value=1>```

>>> cam.controls["saturation"]
<Control saturation type=integer min=0 max=100 step=1 default=64 value=64>
>>> cam.controls["saturation"].id
9963778
>>> cam.controls[9963778]
<Control saturation type=integer min=0 max=100 step=1 default=64 value=64>

>>> cam.controls.brightness
<Control brightness type=integer min=0 max=255 step=1 default=128 value=64>
>>> cam.controls.brightness.value = 128
>>> cam.controls.brightness
<Control brightness type=integer min=0 max=255 step=1 default=128 value=128>

asyncio

v4l2py is asyncio friendly:

$ python -m asyncio

>>> from v4l2py import Device
>>> with Device.from_id(0) as camera:
...     async for frame in camera:
...         print(f"frame {len(frame)}")
frame 10224
frame 10304
frame 10224
frame 10136
...

(check examples/basic_async.py)

gevent

v4l2py is also gevent friendly:

$ python

>>> from v4l2py import Device, GeventIO
>>> with Device.from_id(0, io=GeventIO) as camera:
...     for frame in camera:
...         print(f"frame {len(frame)}")
frame 10224
frame 10304
frame 10224
frame 10136
...

(check examples/basic_gevent.py and examples/web/app.py)

Bonus track

You've been patient enough to read until here so, just for you, a 20 line gem: a flask web server displaying your device on the web:

$ pip install flask

# web.py

import flask
from v4l2py import Device

app = flask.Flask('basic-web-cam')

def gen_frames():
    with Device.from_id(0) as cam:
        for frame in cam:
            yield b"--frame\r\nContent-Type: image/jpeg\r\n\r\n" + frame.data + b"\r\n"

@app.route("/")
def index():
    return '<html><img src="/stream" /></html>'

@app.route("/stream")
def stream():
    return flask.Response(
        gen_frames(), mimetype='multipart/x-mixed-replace; boundary=frame')

run with:

$ FLASK_APP=web flask run -h 0.0.0.0

Point your browser to 127.0.0.1:5000 and you should see your camera rolling!

Migrating from 1.x to 2

A frame changed from a simple bytes object to a Frame which contains the data plus all frame metadata.

As a consequence, when migrating from 1.x to 2, you will need to cast frame object with bytes or access the frame.data item:

Before:

with Device.from_id(0) as cam:
    for frame in cam:
        buff = io.BytesIO(frame)

Now:

with Device.from_id(0) as cam:
    for frame in cam:
        frame = bytes(frame)  # or frame = frame.data
        buff = io.BytesIO(frame)

References

See the linux/videodev2.h header file for details.

• Video for Linux Two Specification <http://linuxtv.org/downloads/v4l-dvb-apis/ch07s02.html>