Initial implementation of an example tool to take a snapshot and save…

… it to a .jpg file

examples/v4l2py-snapshot.py

@@ -0,0 +1,135 @@
+import argparse
+import time
+import datetime
+import sys
+
+from v4l2py.device import Device, VideoCapture, PixelFormat
+from v4l2py.device import iter_video_capture_devices, Capability
+
+
+def list_devices() -> None:
+    print("Listing all video capture devices ...\n")
+    for dev in iter_video_capture_devices():
+        with dev as cam:
+            print(f"{cam.index:>2}: {cam.info.card}")
+            print(f"\tdriver  : {cam.info.driver}")
+            print(f"\tversion : {cam.info.version}")
+            print(f"\tbus     : {cam.info.bus_info}")
+            caps = [
+                cap.name.lower()
+                for cap in Capability
+                if ((cam.info.device_capabilities & cap) == cap)
+            ]
+            if caps:
+                print("\tcaps    :", ", ".join(caps))
+            else:
+                print("\tcaps    : none")
+            print("\tframesizes:")
+            frame_sizes = supported_frame_sizes(cam.info.frame_sizes)
+            for i in range(len(frame_sizes)):
+                s = frame_sizes[i]
+                print(f"\t  {i+1:2}: {s[0]:4} x {s[1]:4}")
+        print()
+
+
+def supported_frame_sizes(frame_sizes, pixel_format=PixelFormat.MJPEG):
+    sfs = [(f.width, f.height) for f in frame_sizes if f.pixel_format == pixel_format]
+    sfs.sort()
+    return sfs
+
+
+def take_snapshot(args):
+    with Device(args.device) as cam:
+        capture = VideoCapture(cam)
+        if args.framesize == 0:
+            (width, height, _) = capture.get_format()
+        else:
+            framesizes = supported_frame_sizes(cam.info.frame_sizes)
+            try:
+                fmt = framesizes[args.framesize - 1]
+            except IndexError:
+                print(f"ERROR: framesize index {args.framesize} not available")
+                sys.exit(1)
+            else:
+                (width, height) = fmt
+        print(f"Framesize is {width}x{height} pixels")
+        capture.set_format(width, height, "MJPG")
+
+        print(f"Camera warmup for {args.warmup}ms ...")
+        warmup_ = args.warmup * 1000000
+        start = time.monotonic_ns()
+        for frame in cam:
+            if time.monotonic_ns() - start >= warmup_:
+                break
+        print("Camera is ready")
+
+    print("Snapshot taken")
+    return frame
+
+
+def save_snapshot(frame, args):
+    now = datetime.datetime.now()
+    fname = now.strftime(args.filename)
+    print(f"Saving as {fname} ...")
+    with open(fname, "wb") as f:
+        f.write(frame.data)
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(
+        prog="v4l2py-snapshot",
+        description="Example utility to get a picture from a capturing device and save it to disk.",
+    )
+    parser.add_argument(
+        "-d",
+        "--device",
+        type=str,
+        default="0",
+        metavar="<dev>",
+        help="use device <dev> instead of /dev/video0; if <dev> starts with a digit, then /dev/video<dev> is used",
+    )
+    parser.add_argument(
+        "-f",
+        "--framesize",
+        type=int,
+        default=0,
+        metavar="<size>",
+        help="set framesize, check --list-devices for supported sizes (default: 0 = whatever is currently set)",
+    )
+    parser.add_argument(
+        "-w",
+        "--warmup",
+        type=int,
+        default=3000,
+        metavar="<msec>",
+        help="time (in miliseconds) to wait before snapshot is taken, to let camera adjust to environment (default: %(default)s)",
+    )
+    parser.add_argument(
+        "-F",
+        "--filename",
+        type=str,
+        default="DSC-%Y%m%d-%H%M%S.jpg",
+        metavar="<filename>",
+        help="name of the file to save the captured frame to (supports datetime.strftime variables) (default: %(default)s)",
+    )
+
+    actions = parser.add_argument_group("Actions")
+    actions.add_argument(
+        "--list-devices",
+        default=False,
+        action="store_true",
+        help="list all video capture devices",
+    )
+
+    args = parser.parse_args()
+
+    if args.device.isdigit():
+        args.device = f"/dev/video{args.device}"
+
+    if args.list_devices:
+        list_devices()
+    else:
+        frame = take_snapshot(args)
+        save_snapshot(frame, args)
+
+    print("Done.")