I recently built an application where I wanted to write some arbitrary text onto a video. I was using Expression Encoder 4 and had a difficult time finding some examples and documentation, aside from some basic MSDN documentation on the MediaItem class. I was eventually able to figure it out, but it took a little time. Even though the end result is not particularly glamorous, I thought I’d save you some time and share what I learned.
The first thing to recognize is that you have to create a Bitmap of the text you want to overlay. This Bitmap is then overlayed on to the MediaItem. So, first things first, create your Bitmap. Here’s an approach:
1. /// <summary>
2. /// This method will create a bitmap based
3. /// </summary>
4. /// <param name="overlayText"></param>
5. /// <param name="rootPath"></param>
6. /// <param name="width"></param>
7. /// <param name="height"></param>
8. /// <returns></returns>
9. private static string createOverlayImage(string overlayText, string rootPath, int width, int height)
10. {
11. // full path for a temporary bitmap
12. string overlayFileName = rootPath + "\\" + Guid.NewGuid().ToString() + ".bmp";
13.
14. // create a bitmap
15. Bitmap bitmap = new Bitmap(width, height);
16. Graphics g = Graphics.FromImage(bitmap);
17.
18. // define the font
19. Font font = new Font("Arial", (float)14.0);
20.
21. // define the area to draw on
22. Rectangle area = new Rectangle(new Point(0, 0), new Size(width, height));
23.
24. // draw the new image
25. g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAlias;
26. g.DrawString(overlayText, font, Brushes.Red, area);
27.
28. // save the picture with the text overlay
29. bitmap.Save(overlayFileName);
30.
31. // return the path to the overlay image
32. return overlayFileName;
33. }
Nothing too surprising here:
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Line #9: Pass in the text you want to overlay, the path for where you’ll store the created bitmap, and the width/height.
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Line #12: Create a random file name for the Bitmap.
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Line #26: You can change the font, color, and locations here if you’d like.
Now, with this method, you can set the overlay properties on the MediaItem like this:
1. // sets file name to media item
2. mediaItem = new MediaItem("test.wmv");
3.
4. // create the overlay image and return the path
5. string overlayFileName = createOverlayImage("Thank you for encoding this video!", Environment.CurrentDirectory, mediaItem.VideoSize.Width, mediaItem.VideoSize.Height);
6.
7. // create the overlay on the media item
8. mediaItem.OverlayFileName = overlayFileName;
9. mediaItem.OverlayLayoutMode = OverlayLayoutMode.WholeSequence;
10. mediaItem.OverlayRect = new Rectangle(new Point(30, 10), new Size((mediaItem.VideoSize.Width - 30), (mediaItem VideoSize.Height - 10)));
Breaking it down:
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Line #5: Grab the full path to the newly created Bitmap over your text overlay.
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Line #8: Set the OverlayFileName to your Bitmap.
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Line #9: Choose the layout mode. There are a few options here that you can explore; details are on MSDN.
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Line #10: The OverlayRect defines where your Bitmap lives on the video. I indented it a bit, but it’s up to you.
I’ve modified the Simple template provided by the Expression Encoder 4 SDK with the code. You can find it below. Hope this helps.