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Text overlays

Text over video frames

Each text overlay is identified by its index, passed as the first parameter of the SetTextOverlay... and GetTextOverlay... functions: index 0 for the 1st text overlay, index 1 for the 2nd text overlay, etc.

To draw a text overlay over the video frames:

E.g., frame number drawn in the top-left corner by the 1st text overlay (index 0):

VideoGrabber.SetTextOverlay_String (0, "frame number: %frame_count%")
VideoGrabber.SetTextOverlay_Left (0, 10)
VideoGrabber.SetTextOverlay_Top (0, 10)
VideoGrabber.SetTextOverlay_FontSize (0, 12)
VideoGrabber.SetTextOverlay_Transparent (0, true)
VideoGrabber.SetTextOverlay_Enabled (0, true)

Remark: a shadow can be drawn under the text overlay when SetTextOverlay_Shadow is enabled, according to the SetTextOverlay_ShadowDirection and SetTextOverlay_ShadowColor values.

Alpha blending

To enable the alpha blending of a text overlay:

Text scrolling

The text scrolling is activated by SetTextOverlay_Scrolling (Index, true).
The scrolling speed is adjusted with SetTextOverlay_ScrollingSpeed (Index, Speed):

  • Speed > 0 -> scrolling from right to left
  • Speed < 0 -> scrolling from left to right
  • Speed = 0 -> stops the scrolling

When scrolling is completed (when the last character disappears from the video frame) the OnTextOverlayScrollingCompleted event occurs.
Its TextOverlayIndex parameter returns the index of the related text overlay (0 for the 1st text overlay, 1 for the 2nd, etc.).

Custom fonts

A fully customized font can be created by invoking TextOverlay_CreateCustomFont (Index, ...): the parameters after the index are those of the Windows CreateFont function.

E.g., Wingdings font for the 1st text overlay (index 0):

VideoGrabber.TextOverlay_CreateCustomFont (0, 16, 30, 0, 0, 200, true, false, false, 2, 0, 0, 0, 0, "Wingdings")

Using several text overlays, each one having its own font / color / background

Up to 1000 text overlays can be drawn at the same time over the video frames, each one with its own string, font, colors, location, etc. Simply pass the index of the text overlay as the first parameter of the SetTextOverlay... functions.

E.g.:

  • frame number in the top-left corner for the 1st text overlay (index 0):
VideoGrabber.SetTextOverlay_String (0, "frame number: %frame_count%")
VideoGrabber.SetTextOverlay_Left (0, 10)
VideoGrabber.SetTextOverlay_Top (0, 10)
VideoGrabber.SetTextOverlay_FontSize (0, 12)
VideoGrabber.SetTextOverlay_Transparent (0, true)
VideoGrabber.SetTextOverlay_Enabled (0, true)
  • frame time in the top-right corner, on an opaque background, for the 2nd text overlay (index 1):
VideoGrabber.SetTextOverlay_String (1, "frame time: %time_100ns%")
VideoGrabber.SetTextOverlay_Left (1, VideoGrabber.VideoWidth - 120)
VideoGrabber.SetTextOverlay_Right (1, VideoGrabber.VideoWidth)
VideoGrabber.SetTextOverlay_Top (1, 60)
VideoGrabber.SetTextOverlay_FontSize (1, 8)
VideoGrabber.SetTextOverlay_Transparent (1, false)
VideoGrabber.SetTextOverlay_Enabled (1, true)
  • hiding the frame time, drawn by the 2nd text overlay (index 1):
VideoGrabber.SetTextOverlay_Enabled (1, false)

Remark: ***
TVideoGrabber does not allocate the resources of the 1000 text overlays at startup. The font and the settings of a text overlay are allocated the first time its index is used, together with all the lower indexes not yet allocated.
E.g. if the text overlays 0 to 4 are already allocated and the index 20 is used, the text overlays 5 to 20 are allocated as well (16 new fonts and parameter sets, for a total of 21).
So use consecutive indexes starting at 0: e.g. for 5 different text overlays, use the indexes 0 to 4 and never a greater index, to prevent allocating useless fonts and parameter sets.*