FBC — Video Frame Index (.FBC)¶
Companion index file for a .VDO video. Provides the byte size of each frame
so that a decoder can seek directly to any frame without scanning the video
data. Found in FA_7.LIB: exactly one .FBC per .VDO, sharing the same
4-character stem (355 pairs). Audio pairs differently — by 3-character prefix,
not by full stem (see § Relationship to .VDO).
Tools¶
fx¶
fx fbc info <file.FBC> # frame count + expected paired-VDO size
fx fbc ls <file.FBC> # per-frame size and VDO offset table
fx_lib round-trips the format byte-identically (fbc_read/fbc_write);
the fxs VDO editor renders the same index through the library.
File Layout¶
All multi-byte integers are little-endian.
No magic or header. The file is a flat array of N u32 values, where N equals
the frame count stored in the paired .VDO header (offset 16). File size is
always 4 × N bytes.
| Offset | Size | Type | Description |
|---|---|---|---|
0x00 |
4 × N | u32[N] | Byte size of each frame in the paired .VDO |
Relationship to .VDO¶
frame_data_offset(n) = 816 + sum(FBC[0 .. n-1])
invariant: sum(FBC[0 .. N-1]) == VDO_file_size - 816
N also equals the frame-count u16 at VDO header offset 0x10 (confirmed).
Verified against the full corpus (#137). All 355 .FBC/.VDO pairs in
FA_7.LIB satisfy the invariant with zero mismatches; frame counts range 12 →
1685 (41,163 frames total). Every .VDO has exactly one same-stem .FBC.
Audio pairing is by 3-character prefix, not full stem. The .11K narration
files use a 3-character stem (e.g. AAC.11K) shared across all 4-character
.VDO variants of that briefing group (AACA, AACB, … — the 4th character
A–J is the variant/angle). Of the 105 briefing-group prefixes, 104 carry
audio; one group (IQC) is silent. So a .VDO is not guaranteed a
same-stem .11K — it shares its group's track (if any).
Observed Values¶
Representative pairs (the invariant is verified across all 355 — see above):
| File | Entries (N) | FBC size | VDO size | VDO size − 816 |
|---|---|---|---|---|
| ABCA.FBC | 68 | 272 | 113,353 | 112,537 |
| AACA.FBC | 123 | 492 | 156,301 | 155,485 |
| AACB.FBC | 260 | 1040 | 362,853 | 362,045 |
| IPCA.FBC | 1685 | 6740 | 13,141,769 | 13,140,953 |
Related¶
Formats: VDO — the video stream this file indexes; 11K — the audio track, shared per 3-character briefing-group prefix.
Engine: the fxs VDO editor renders this index (frame table); the fx_lib codec is tracked in #107.