AVI Wrapped to the right slightly

[bassill]

AVI Wrapped to the right slightly

[baSSiLL]

Hi
It's not apparent from the image how it should look like normally. But as soon as vertical lines don't get inclined I suppose there's a constant shift in bitmap data. Probably, a wrong start of bitmap data is specified.
What is the source of frames? How do you pass frames to SharpAvi? Which encoder do you use?

[stevehjohn]

Hi,

Thanks for responding. The bitmaps are captured from the screen with the following code:

https://github.com/stevehjohn/AoC/blob/a4bbe7321ff5b22fae0c65c936288eed8ad9dc00/AoC.Visualisations/Infrastructure/VisualisationBase.cs#L84

To test, I added some debug code to save the bitmap. When I opened it in Paint.Net, it looked correct.

You can see the video here: https://youtu.be/eAzu7xScquA?t=83
From about 1:20 there is a stream of water that should be at the very right hand edge of the frame, but as you can see, it is wrapped around to the left.

Thanks,

Steve.

[baSSiLL]

I see. You should not save a bitmap to the BMP format before passing to SharpAvi. This way the array you pass to WriteFrame contains not only raw pixel data but also a few excess bytes in the beginning coming from the BMP header. Hence the shift in pixels.
Take a look to a similar code in the sample app.

SharpAvi/Sample/Recorder.cs

Line 228 in 02b1447

var bits = bitmap.LockBits(new Rectangle(0, 0, screenWidth, screenHeight), ImageLockMode.ReadOnly, PixelFormat.Format32bppRgb);

You just call LockBits' to get a pointer to a Bitmap's pixel data. And then you can either copy it to an array, a MemoryStreamor other managed memory. Or use unsafe code and create aSpandirectly from the pointer which you can then pass toWriteFrame`.

var bits = bitmap.LockBits(new Rectangle(0, 0, bitmap.Width, bitmap.Height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
var span = new Span<byte>(bits.Scan0.ToPointer(), bits.Stride * bits.Height);
videoStream.WriteFrame(true, span);
bitmap.UnlockBits(bits);

[stevehjohn]

Hi,

That seems to have fixed the alignment issue. However the AVI is now upside-down.

Thanks,

Steve.

[baSSiLL]

You use an uncompressed video stream without an encoder, it expects pixel data in the bottom-up direction. It worked with the BMP format because it also stores pixels in the bottom-up direction. While the Bitmap class stores its data in the top-down direction.
You can turn to UncompressedVideoEncoder which expects top-down data and performs the necessary vertical flipping under the hood. Note that you'll also need to change the bitmap format to PixelFormat.Format32bppRgb as all encoders in SharpAvi expect pixel data in this format.

[stevehjohn]

Perfect, that all works now.

Thank-you for your help with this issue. I presume my original issue was caused by header information that is added when saving a bitmap?

Thanks,

Steve.

[baSSiLL]

I presume my original issue was caused by header information that is added when saving a bitmap?

Correct

[stevehjohn]

Cool.

Once again, thanks for your help with this!

Steve.

[stevehjohn]

Appreciate your help, gave you a shout out here: https://www.outsidecontextproblem.com/threading.html

Cheers,

Steve.