Using Graphics Files to Create an Animation
While subtitles are most often used to present text, the ability to import graphics files
into subtitle streams makes it possible to use them for other purposes. For example, the
video stream might show a mountain while the subtitle shows the route taken to climb
it with a line that gradually grows from the start of the trail to the mountain top.
While you cannot import any kind of a motion asset into a subtitle stream, you can
manually create an animation by adding a number of very short (one- or two-frame)
subtitles, each with a different graphic that shows the line at a different stage.
Typical text subtitles have little impact on the playback bit rate—on average they run at
around 10 kbps. When you use subtitles to create an animation, the impact on the playback
bit rate becomes substantial, and may force you to lower the bit rate of the video stream.
The DVD specification limits a subtitle stream’s bit rate to 3.36 Mbps (about the same as
some MPEG-2 video).
The easiest way to create a subtitle animation is to create an STL subtitle file and import
it. You can specify the exact duration and position of each graphic, as well as configure
the color mapping settings. See
Creating an STL Format Subtitle File
for more information.