VideoCharacteristics not detected about flashcap

[SignalMQ]

@kekyo I'm tried to detect my device with V4L2 Devices().Enumerate Descriptors() and surprised for detected 2nd shadow copy of device placed in /dev/video0:

Here it seemed strange to me that the devices are listed in reverse order ([/dev/video1, /dev/video0]), or I’m wrong.

[SignalMQ]

My problem solved, I use my second device.

[kekyo]

@SignalMQ The next version will support NV12 format. Perhaps devices that were not enumerated (or were Unknown) will become available, so if you are interested, please give it a try.

[kekyo]

Thanks for reached out!

If FlashCap is the latest, Characteristics cannot handle are also enumerated as Unknown formats. However, I could not understand why they are not enumerated at all, including them. Can we try other cameras?

[SignalMQ]

I tried code below on my second computer:

using FlashCap;
using SkiaSharp;

var devices = new CaptureDevices();
var descriptor0 = devices.EnumerateDescriptors().ElementAt(0);
byte[] imageData = await descriptor0.TakeOneShotAsync(descriptor0.Characteristics.FirstOrDefault());

using (var ms = new MemoryStream(imageData))
{
    SKBitmap bitmap = SKBitmap.Decode(ms);
    SKFileWStream fs = new("photo.png");
    bitmap.Encode(fs, SKEncodedImageFormat.Png, quality: 100);
}

Other cam:
Logi C270 HD WebCam (USB\VID_046D&PID_0825&MI_00\6&29B00C26&0&0000)

OS:
Windows 11 Enterprise 22H2

Detected and works perfectly, but in my laptop same situation

Result:

[SignalMQ]

Thanks for reached out!

If FlashCap is the latest, Characteristics cannot handle are also enumerated as Unknown formats. However, I could not understand why they are not enumerated at all, including them. Can we try other cameras?

I dont have other cameras on this device, because it's laptop.

[kekyo]

@SignalMQ On #126 and #127, maybe these issues were a factor. #124 may also affect stable operation, so can I try it after merging these?

[SignalMQ]

@SignalMQ On #126 and #127, maybe these issues were a factor. #124 may also affect stable operation, so can I try it after merging these?

I don't understand, what you meaning in 'so can I try it...'. I'm try these fixes or you?

[kekyo]

Oh, sorry if it doesn't make sense, I made a mistake in the translation program 😵‍💫
Could you try it with a commit from current develop branch?

[SignalMQ]

Hello @kekyo. I am building nupkg from develop branch but this error appears above.

[SignalMQ]

Characteristics [VideoCharacteristics[]]:
{FlashCap.VideoCharacteristics[0]}
Description [string]:
"usb-0000:03:00.4-3: uvcvideo"
DeviceType [DeviceTypes]:
V4L2
Identity [object]:
"/dev/video1"
Name [string]:
"USB2.0 HD UVC WebCam: USB2.0 HD"
Non-Public members

here is my decriptors info

[kekyo]

@SignalMQ Sorry later, I am interested in what characteristics are enumerated in your camera. The following sections:

https://github.com/kekyo/FlashCap/blob/854186a445e494548480ae0d6b607c1bf009eb57/FlashCap.Core/Devices/V4L2Devices.cs#L184C29-L184C48

                        return (CaptureDeviceDescriptor)new V4L2DeviceDescriptor(
                            devicePath, ToString(caps.card), $"{ToString(caps.bus_info)}: {ToString(caps.driver)}",
                            EnumerateFormatDesc(fd).
                            SelectMany(fmtdesc =>
                                EnumerateFrameSize(fd, fmtdesc.pixelformat).
                                SelectMany(frmsize =>
                                    EnumerateFramesPerSecond(fd, fmtdesc.pixelformat, frmsize.Width, frmsize.Height).
                                    Collect(framesPerSecond =>
                                        NativeMethods_V4L2.CreateVideoCharacteristics(
                                            fmtdesc.pixelformat, frmsize.Width, frmsize.Height,
                                            framesPerSecond.Value, ToString(fmtdesc.description),
                                            frmsize.IsDiscrete && framesPerSecond.IsDiscrete)))).
                            Distinct().
                            OrderByDescending(vc => vc).
                            ToArray());

Here, if a series of SelectMany() returns no result, the number of characteristics is zero. Such a possibility would be if EnumerateFormatDesc(), EnumerateFrameSize(), or EnumerateFramesPerSecond() returned zero elements. Your camera may fall into one of these cases.

This line is written on a single line, so it may be difficult to verify. For example:

var a = EnumerateFormatDesc(fd).ToArray();
var b = a.SelectMany(fmtdesc =>
{
    var c = EnumerateFrameSize(fd, fmtdesc.pixelformat).ToArray();
    var d = c.SelectMany(frmsize =>
    {
        // ...
    });
    // ...
});

to change the enumeration so that you can check the enumeration and be sure of it on the debugger.

[kekyo]

I was surprised too! I'm not sure why there are multiple /dev/video? enumerations in the first place, but I'm not particularly aware of the order:

FlashCap/FlashCap.Core/Devices/V4L2Devices.cs

Line 171 in 854186a

Directory.GetFiles("/dev", "video*").

If you select /dev/video1, will it capture correctly?

[SignalMQ]

I was surprised too! I'm not sure why there are multiple /dev/video? enumerations in the first place, but I'm not particularly aware of the order:

FlashCap/FlashCap.Core/Devices/V4L2Devices.cs

Line 171 in 854186a

Directory.GetFiles("/dev", "video*").

If you select /dev/video1, will it capture correctly?

/dev/video1 - fail
/dev/video0 - sucess

[kekyo]

According to the screenshot, /dev/video0 has zero characteristics and /dev/video1 enumerates several characteristics, did you succeed in the case of /dev/video0?

Are you saying that you used the value of /dev/video1 as the characteristic in that case?

[SignalMQ]

According to the screenshot, /dev/video0 has zero characteristics and /dev/video1 enumerates several characteristics, did you succeed in the case of /dev/video0?

Are you saying that you used the value of /dev/video1 as the characteristic in that case?

/dev/video0 has 12 characteristics and it's work, but /dev/video1 enumerated in first is not work, because don't have any characteristics listed.

[kekyo]

I see. As a coping remedy, it seems that we need to ignore devices with zero characteristics.

We could ignore devices with zero characteristics when internal FlashCap enumerates them, but I imagine that would probably make it difficult to identify the problem.
Therefore, I would like to make it a policy that this exclusion is handled by the caller. For example:

if (devices.EnumerateDescriptors().
    FirstOrDefault(d => d.Characteristics.Any(c => c.PixelFormat != PixelFormats.Unknown)) is { } device)
{
    // `device` is valid.
}