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Globotix / usb_cam

(ARCHIVED) A ROS Driver for V4L USB Cameras
http://wiki.ros.org/usb_cam
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Using framerate <= 30 shows error on new h264_yuv420p pixel_format #1

Open LKSeng opened 2 years ago

LKSeng commented 2 years ago

Example error:

[ERROR] [1647765946.2751156857]: Webcam: expected picture but didn't get it...

LKSeng commented 2 years ago

After some investigation, the following were elucidated:

Setting frame_rate > 30 causes frames to be published at ~30.5s, but the above error does not show anymore. Setting frame_rate == 30 causes frames to be published at ~30.1s, but the above error does appear occasionally. Setting frame_rate < 30 causes the above error to appear more periodically.

I read a stackexchange answer suggesting that the frame rates are fixed by the device, and [sic] it is the user's responsibility to read at a higher rate [/sic] (when using h264).

Therefore, when h264 is used, please set the frame rate to something slightly larger than the framerate allowable by the device.

i.e.

$ v4l2-ctl -d /dev/video4 --list-formats-ext

You'll see something like:

ioctl: VIDIOC_ENUM_FMT
    Type: Video Capture

    [0]: 'H264' (H.264, compressed)
        Size: Discrete 1920x1080
            Interval: Discrete 0.033s (30.000 fps)
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 1280x720
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 640x480
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 640x360
            Interval: Discrete 0.033s (30.000 fps)
        Size: Discrete 1920x1080
            Interval: Discrete 0.033s (30.000 fps)
            Interval: Discrete 0.033s (30.000 fps)

So set the frame_rate to, say, 31 fps when using h264_yuv420p.

LKSeng commented 2 years ago

If you device supports MJPEG, do consider using the stream mentioned in #2 as a workaround instead. It seems that the MJPEG stream is less picky on the read interval as compared to H264.