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Blu-ray Subtitle Creator
Adding lines of subtitle text for the video is supported in Blu-ray authoring routines. Two approaches for creating subtitles are described according to the Blu-ray Specifications -
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Presentation Graphics
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Text Subtitle
In Presentation Graphics
method, it generates a
Presentation Graphics
Stream
containing information required to provide
images that are supplemental to an associated HDMV
presentation. The images described in the stream are
designed for graphic overlay, with frame accuracy, on the
associated HDMV video image. It is
envisaged that HDMV Presentation Graphics streams will
typically be used to provide subtitle services
during a HDMV presentation.
In Text Subtitle method, it generates a Text subtitle stream containing information required to provide rendered images that are supplemental to an associated HDMV presentation. The rendered images specified by HDMV Text subtitle decoder is designed for subtitle overlay, with frame accuracy, on the associated HDMV video image. It is envisaged that a HDMV Text subtitle stream will typically be used to provide a subtitle service during a HDMV presentation.
Presentation Graphics requires images to be rendered prior to the presentation. Text Subtitle requires text input (character input) and images are to be rendered during presentation by the decoder.
In this SDK, only Presentation Graphics is supported.
User has to prepare subtitles in bitmap before running authoring routines. Each bitmap represents a frame of subtitle. The following example depicts a subtitle frame having two text lines.
The bitmap frame size shall be at least to conclude all text characters. The text line(s) can be placed at any spot within the frame space. Blu-ray Spec allows each pixel in the subpicture frame to be painted in one of 255 colors. In this SDK, white (RGB 255,255,255) only represents full transparency (zero value of opacity). The input RGB color will be converted to be YCbCr in YUV color space.
User may prepare all subtitle bitmaps and may write each bitmap file path to a text file. The text will be imported to BDLIB library and each bitmap file will be entered to the compression routine in the library. Along with bitmap file paths, user also needs to identify and to write the start-time and the end-time for each subtitle frame to be displayed. The start-time is the time that the subtitle frame starts displaying. The end-time is the time that the subtitle frame stops displaying. The end-time cannot be earlier than the start-time.
Sample text file:
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subtitle file mark%bmp |
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00:00:10:000&00:00:30:000&2%c:\sub0.bmp |
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00:00:50:000&00:01:10:000&1%c:\sub1.bmp |
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00:01:20:000&00:01:40:000&0%c:\sub2.bmp |
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00:01:50:000&00:02:00:000&2%c:\sub3.bmp |
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00:02:11:000&00:02:13:000&3%c:\bmp5.bmp |
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00:02:13:000&00:02:15:000&2%c:\bmp6.bmp |
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00:02:25:000&00:02:27:000&0%c:\bmp7.bmp |
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00:03:17:000&00:03:29:000&2%c:\bmp8.bmp |
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00:03:31:000&00:03:35:000&2%c:\bmp9.bmp |
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... |
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end |
Notes:
Each input file shall have a file mark. The file mark has to be in the following format:
Subtitle File Mark%bmp
A subtitle type ( ' bmp ' or ' txt ' ) shall be attached right after the marker.
' time code ' - The first column represents start appearing time code in hh:mm:ss:msec format. The second column represents end appearing time code in the same format.
' positioning' - 0 --- Central placement, 1 --- Left margin placement, 2 --- Right margin placement
' bmp file path ' - The full path of subtitle bitmap file.