Add decoder support for pixel format BGRA & ARGB

[zyxar]

Description

This PR adds decoder support for pixel format BGRA & ARGB, and enables them in pkg avfoundation.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 36 lines in your changes missing coverage. Please review.

Project coverage is 44.22%. Comparing base (20e8c50) to head (a5c1294).

Files with missing lines	Patch %	Lines
pkg/frame/rgb.go	0.00%	28 Missing ⚠️
pkg/avfoundation/avfoundation_darwin.go	0.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #315      +/-   ##
==========================================
- Coverage   44.51%   44.22%   -0.29%     
==========================================
  Files          80       81       +1     
  Lines        5556     5592      +36     
==========================================
  Hits         2473     2473              
- Misses       2913     2949      +36     
  Partials      170      170              

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[at-wat]

It seems like a conversion from ARGB to GRAB. (frame[i] is A and frame[i+2] is G in the original ARGB data)
Maybe the implementations of decodeARGB and decodeBGRA are swapped?

[zyxar]

I think it only matters to the name of the pixel format.

according to libyuv formats:

kCMPixelFormat_32ARGB          = 32,      FOURCC_BGRA
kCMPixelFormat_32BGRA          = 'BGRA',  FOURCC_ARGB

and I use the FOURCC_* naming to to name frame.FormatBGRA and frame.FormatARGB which results a similar mapping in avfoundation pkg.

[at-wat]

Sorry, I misread endian. (It should be little endian on x86 and ARM)

This func seems converting 0xXXYYZZWW (input) to 0xXXWWZZYY (output).
As the output byte order for image.RGBA is RGBA order (XX=A, WW=B, ZZ=G, YY=R on little endian uint32), input byte order shoud be BGRA.

I guess
https://github.com/pion/mediadevices/pull/315/files#diff-99707109ce57457c8ab1161707d059373858d14ae66e06aed05c50501e29eaa6R148-R153
https://github.com/pion/mediadevices/pull/315/files#diff-99707109ce57457c8ab1161707d059373858d14ae66e06aed05c50501e29eaa6R179-R184
are reversed and name of decodeARGB and decodeBGRA should be swapped?

(I don't have any Macintosh computers, so I couldn't test it on the real environment.)

[at-wat]

BGRA to GRAB ?

[at-wat]

It would be nice to have a simple test like:

mediadevices/pkg/frame/yuv_test.go

Lines 10 to 41 in dafd208

	func TestDecodeYUY2(t *testing.T) {
	const (
	width = 2
	height = 2
	)
	input := []byte{
	// Y Cb Y Cr
	0x01, 0x82, 0x03, 0x84,
	0x05, 0x86, 0x07, 0x88,
	}
	expected := &image.YCbCr{
	Y: []byte{0x01, 0x03, 0x05, 0x07},
	YStride: width,
	Cb: []byte{0x82, 0x86},
	Cr: []byte{0x84, 0x88},
	CStride: width / 2,
	SubsampleRatio: image.YCbCrSubsampleRatio422,
	Rect: image.Rect(0, 0, width, height),
	}
	decoder, err := NewDecoder(FormatYUY2)
	if err != nil {
	t.Fatal(err)
	}
	img, _, err := decoder.Decode(input, width, height)
	if err != nil {
	t.Fatal(err)
	}
	if !reflect.DeepEqual(expected, img) {
	t.Errorf("Wrong decode result,\nexpected:\n%+v\ngot:\n%+v", expected, img)
	}
	}

[edaniels]

HI @zyxar, do you still want to get this in?