RGB to YUV420 mistake about openh264lib.net

[secile]

Hello, thank you for your information.

I noticed this problem when I first made this library.
In line 58 of Decoder.cpp, there is a comment 'なぜかuvが逆' (in Japanese)
that means 'I don't know why, but it works if U and V are reversed.'
I thought something wrong, but it's working fine, so I left it as it is.

This time, I investigated the reason. and I found that some little problem makes this issue.

When I encoded PNG images of blue(RGB=0000FF) to h264 movie file, blue element of movie file became RGB=113EFF.
Similarly, I encoded red(RGB=FF0000), then became RGB=CD0000. It is strange. Color is almost same, but the color has changed a little.

before encode(PNG)	after encode(h264)
RGB=0000FF	RGB=113EFF
RGB=FF0000	RGB=CD0000

I found some problems.

• In C#, pixel order of Bitmap is 'BGR', but my code assumed that pixel order is 'RGB'.
• Since element 'B' and 'R' is swapped, V plane and U plane is swapped.
• Since B-V conversion formula is different from R-U, the color has changed.

I fixed these problems, and test again. I think color changing problem is solved.

before encode(PNG)	after encode(h264)
RGB=0000FF	RGB=0000FC
RGB=FF0000	RGB=FD0001

I'm currently working on a fix for this issue. After that, I will update my repository.
If you have any comment please let me know.

Thank you.