Hardware MJPEG encoding, any implementation?

[SteveSpencer]

Hi. I am looking at the possibility of porting my camera server which runs on bookworm on a Pi ZeroW, to make a cheap and cheerful IP camera (no zoom, no pan, no tilt).

It provides an MJPEG stream via http (and that's just about all it does), so it seems an ideal candidate to strip all the unnecessary OS components out. In addition, following a house move late last year, I want to put a couple of cameras around the garden. However, occasional power-outs mean I have had to reimage the uSD cards a couple of times. and Circle isn't as vulnerable to that, since once it's booted, there is a lot less disk activity.

Pi4 and earlier have jpeg encoding hardware, while the Pi5 doesn't, but is fast enough to handle the encoding in software.
Is there a way to have the earlier hardware do the encoding of the image, as I do with the linux libcamera?
It seems like a big ask, as I have no idea what would be involved.
I did have to derive my own class from Encoder, to specify the output and capture formats.

` v4l2_format fmt = {};
fmt.type = V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE;
fmt.fmt.pix_mp.width = info.width;
fmt.fmt.pix_mp.height = info.height;
fmt.fmt.pix_mp.pixelformat = V4L2_PIX_FMT_YUV420;
fmt.fmt.pix_mp.plane_fmt[0].bytesperline = info.stride;
fmt.fmt.pix_mp.field = V4L2_FIELD_ANY;
fmt.fmt.pix_mp.colorspace = V4L2_COLORSPACE_JPEG;
fmt.fmt.pix_mp.num_planes = 1;
if (xioctl(fd_, VIDIOC_S_FMT, &fmt) < 0)
throw std::runtime_error("failed to set output format");

    fmt = {};
    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
    fmt.fmt.pix_mp.width = options->width;
    fmt.fmt.pix_mp.height = options->height;
    fmt.fmt.pix_mp.pixelformat = V4L2_PIX_FMT_MJPEG;
    fmt.fmt.pix_mp.field = V4L2_FIELD_ANY;
    fmt.fmt.pix_mp.colorspace = V4L2_COLORSPACE_DEFAULT;
    fmt.fmt.pix_mp.num_planes = 1;
    fmt.fmt.pix_mp.plane_fmt[0].bytesperline = 0;
    fmt.fmt.pix_mp.plane_fmt[0].sizeimage = 512 << 10;
    if (xioctl(fd_, VIDIOC_S_FMT, &fmt) < 0)
            throw std::runtime_error("failed to set capture format");

`

Is there a way to do the same ? I'm not sure how the V4L stuff maps to the implementation.
Obviously, this will only be valid for Pi4 and earlier machines, and I would need to provide JPEG encoding for a Pi5 version, but that isn't something I need to worry about right now.

Thanks
Steve Spencer

[rsta2]

Unfortunately I'm afraid this will not work. I'm not aware of any implementation for hardware video/image encoding for Circle.

[SteveSpencer]

OK, thanks. I will trawl through and see if there any bare-metal support for MJPEG for the earlier models. I suspect that the Pi0W just doesn't have enough 'grunt' to do it all in software and run http server code over wifi, in which case I might have to rethink the project.