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Cast Member Storage in .cst Files

The observations below summarize what is currently understood about how Director stores cast members inside .cst files. Points marked as probable are based on limited samples and still need confirmation.

Container structure

  • A .cst file is a RIFX container. The samples seen so far use little‑endian byte order.
  • After the header, an imap chunk provides the offset of the mmap chunk.
  • The mmap (memory map) lists every chunk in the file. Each entry records the FourCC, byte length and file offset of a chunk.

Locating members

  • The CAS* chunk contains the list of cast‑member IDs. This is confirmed by inspecting the CAS* entry in multiple sample files.
  • For each ID, the corresponding CASt entry in the memory map gives the byte offset and length for that member. This behaviour is consistent across all test casts.

CASt chunk layout

A CASt chunk begins with a 12‑byte header:

Offset Field Notes
0 Type Identifies the member type (e.g., 0x0F for a field member).
4 InfoLen Length of the cast‑info block in bytes.
8 SpecificDataLen Length of the member's data block in bytes.
  • After the header, InfoLen bytes form the cast‑info block (Cinf). This block is itself a list of offsets pointing to variable‑length fields such as the member name or script text.
  • The specific data block immediately follows the info block and contains the raw member data (e.g., text characters, bitmap pixels, sound samples).

Member Info Bytes (Cinf Offsets)

Offset Field / Feature Type / Enum Values / Meaning
0x44 CastInfoFlags CastInfoFlags Bit 2 = DTS Off (0 = DTS On, 1 = Off)
0x46 TextFraming TextFraming 0 = Fixed, 1 = Scrolling, 2 = AdjustToFit
0x8E AntiAlias + Kerning TextAntiAlias, TextKerningMode Shared byte — lower nibble = AA, upper nibble = Kerning
0xBA AntiAlias Threshold byte Point size threshold (for AA LargerThan mode)
0xCE Kerning Enable Bit bool Bit 0 = Kerning enabled
0xD2 Kerning Threshold byte Point size threshold (for Kerning LargerThan mode)
0xD6 TextFeatureFlags TextFeatureFlags Bit 0 = UseHyperlinkStyles
0xE6 InkType BlingoInkType Matches Director ink enum (0–41 range)
0xA2 TextMemberFlags TextMemberFlags Bit 0 = IsEditable

Text Framing and Kerning Modes

Enum Value Meaning / Description Source Offset
TextFraming 0x00 Fixed (no scrolling or resizing) Cinf + 0x46
0x01 Scrolling text box Cinf + 0x46
0x02 AdjustToFit (auto-size to content) Cinf + 0x46
TextKerningMode 0x40 None (no kerning adjustments) Cinf + 0x8E
0x30 AllText (kerning applied globally) Cinf + 0x8E
0x70 LargerThan (apply if font > threshold) Cinf + 0x8E
Kerning Enable Bit 0 1 = enabled, 0 = disabled Cinf + 0xCE
Kerning Threshold byte Point-size limit for LargerThan mode Cinf + 0xD2

XMED styled‑text information

  • For text and field members that carry styling, an XMED chunk supplies font and colour runs. The link between a CASt chunk and its XMED data is recorded in the key table (KEY*) and memory map.
  • It is probable that each styled text member references exactly one XMED chunk. Some casts include two copies of the XMED data; the second copy appears to be the one referenced by the memory map, but this needs further verification.

Extracting member data

To extract a member's raw bytes and metadata:

  1. Read the imap chunk to locate the mmap.
  2. Iterate the mmap to build a table of FourCC, offset and length.
  3. Read the CAS* chunk to obtain cast‑member IDs.
  4. For each ID, look up its CASt entry in the memory map to get the byte range.
  5. Within the CASt data:
    • Start of info block = chunkOffset + 8 + 12 (8 for list header, 12 for CASt header).
    • Start of specific data = infoStart + InfoLen.
    • End of member data = specificStart + SpecificDataLen.
  6. If an XMED chunk is referenced, parse it for styled text information.

These steps accurately reproduce the offsets and lengths observed in the sample casts, but additional testing is required to ensure they hold for all files.