BD-ROM Subtitles

The following slides list additional constraints placed on subtitles

  • This is not a complete set of constraints. The BD-ROM spec defines several constraints which will be checked for by the authoring system
If two events overlap, they must share the same 256 colors or be divided into two sets (possibly 128 each)
  • Two subtitles cannot spatially overlap
  • Upto 4MB of 8bit indexed data may be displayed at one time
  • Images may have a maximum width of 4096 and a maximum height of 4096

  • All fonts for a Text subtitle stream must fit in 2MB for non CJK languages. Players that have full support for CJK will have 4MB.
  • Two subtitles cannot spatially overlap
  • Upto 255 Text Subtitle streams may be provided for a piece of content
  • Upto 255 Fonts may be provided per disc
  • Time Interval between the appearance of two Text subtitles must be greater than 1 sec
  • The color or fade of a subtitle may be updated every 2 frames
  • Upto 200 characters per display
  • Rendering speed table
Font size (pixels) Speed (cps)
Without outline border 8-72 50
Without outline border 73-144 25
With outline border 8-54 30
With outline border 55-72 20
With outline border 73-144 10

OpenType Font Format Constraints

(From Annex H.3 – v0.99)
  • An OpenType[38] font resource shall adhere to the syntactic and semantic constraints defined by [OPENTYPE], and shall further satisfy the following constraints:
    1. A referenced font in an OpenType[38] font resource shall specify the value 0x00010000 (1.0) for the sfnt version field in its Offset Table.
      • Note: This specification does not support the use of OpenType[38] fonts containing CFF data, i.e., fonts whose sfnt version is ‘OTTO’.
    2. Each referenced font in an OpenType[38] font resource shall contain a cmap table with Platform ID 3 and Encoding ID 1 (Unicode) using subtable Format 4.
    3. If a referenced font in an OpenType[38] font resource supports rendering a character whose Unicode Scalar Value is greater than 65535, then the font shall contain a cmap table with Platform ID 3 and Encoding ID 10 (UCS-4) using subtable Format 12.
    4. If a referenced font in an OpenType[38] font resource is intended to be used to present vertical text, then it shall contain the following tables: vhea (Vertical Metrics Header) and vmtx (Vertical Metrics).
    5. It shall (1) contain only one font, (2) start with an Offset Table followed by a Table Directory, and (3) use the file or resource name extension “otf”.
    6. The encoding ID in cmap table shall be conformed to the character code indicated by character_code in StreamCodingInfo(), except the case of GB18030- 2000[34