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

Merging #315 (1ff2ff2) into master (3d3830f) will decrease coverage by 0.53%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #315      +/-   ##
==========================================
- Coverage   55.90%   55.37%   -0.54%     
==========================================
  Files          54       55       +1     
  Lines        2277     2299      +22     
==========================================
  Hits         1273     1273              
- Misses        903      925      +22     
  Partials      101      101              

Impacted Files	Coverage Δ
pkg/frame/decode.go	50.00% <ø> (ø)
pkg/frame/rgb.go	0.00% <0.00%> (ø)

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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?