Matthew Jackson
6e14fc0c0c
Security - Remove the unsafe Vec::set_len over recycled sector buffers — UB reachable from safe code (GHSA-j8ww-f5fg-9pmh, low). Uses Vec::resize; pooling unchanged. CI / tooling - clippy on stable with the MSRV single-sourced from Cargo.toml; cargo-deny dependency-audit gate with first-party git sources allowed (#15); audience-based comment-guard (#17). Docs - README (keydb ownership, BD-J parser count), drive-access transport/reset notes, mux timeline module-doc links.
3.4 KiB
VC-1 elementary stream parser — internal notes
Relocated prose from src/mux/codec/vc1.rs internal (non-pub) items, kept
here in full since it exceeds the 3-line internal-comment cap.
parse_vc1_interlace
Read the advanced-profile sequence header's INTERLACE flag (SMPTE 421M
§6.1.1): bit 41 after the start code — after PROFILE(2) LEVEL(3)
COLORDIFF_FORMAT(2) FRMRTQ(3) BITRTQ(5) POSTPROCFLAG(1) MAX_CODED_WIDTH(12)
MAX_CODED_HEIGHT(12) PULLDOWN(1). None for simple/main profile or a header
too short / over-escaped to reach the bit. De-escapes emulation-prevention
bytes first (as parse_vc1_resolution does) so the bit offset is exact.
vc1_progressive_ptype
Decode the advanced-profile progressive picture PTYPE VLC (SMPTE 421M
§7.1.1.4, Table): 0=P, 10=B, 110=I, 1110=BI (intra → I), 1111=
Skipped (predicted, no residual → P). Only valid when the sequence is
progressive — for interlaced an FCM code (and, for field pictures, a combined
FPTYPE) precedes/replaces PTYPE, so the caller declines those.
vc1_frame_coding_type
Measure the coding type of an advanced-profile frame from its picture header.
frame_rbsp starts immediately after the frame start code (00 00 01 0D).
Decodes PTYPE only for a PROGRESSIVE sequence (where PTYPE is the first
picture-layer field); declines (None) for interlaced/simple-main/unknown
rather than guess at the wrong bit offset.
handle_header
Handle a seq_header or entry_point start-code unit (Annex B raw bytes).
Decision is against the currently-ACTIVE body cur, not the codecPrivate
copy first:
- First of its type → seeds codecPrivate; stripped (decoder gets it from the BITMAPINFOHEADER extra data at init).
- Equal to the active set
cur→ redundant; stripped. - Different from
cur(a change in EITHER direction, including reverting to the codecPrivate/first value) → prepended intoprefixin Annex B form andcurupdated.
Returns true when the unit was emitted into prefix.
parse_vc1_resolution
Parse width and height from a VC-1 advanced profile sequence header. The sequence header starts with 00 00 01 0F. After the start code: byte 0 bits 7-6: profile (3 = advanced). Advanced profile seq-header layout (SMPTE 421M, from sh[4]): PROFILE(2)+LEVEL(3)+COLORDIFF_FORMAT(2)+ FRMRTQ_POSTPROC(3)+BITRTQ_POSTPROC(5)+POSTPROCFLAG(1)=16 bits, then MAX_CODED_WIDTH(12)+HEIGHT(12) = 40 bits total = 5 bytes.
make_ap_seq_header (test helper)
Build an advanced-profile VC-1 sequence header encoding the given width/height. Layout from sh[4]: PROFILE(2)=3, LEVEL(3), COLORDIFF(2), FRMRTQ(3), BITRTQ(5), POSTPROCFLAG(1) = 16 bits, then MAX_CODED_WIDTH(12) = width/2 - 1, MAX_CODED_HEIGHT(12) = height/2 - 1.
vc1_emits_entry_point_revert_to_first_value (test)
Regression: entry_point is redefined from A (== codecPrivate) to B, then switched BACK to A. A streaming decoder applied codecPrivate at init and is now on B; the revert to A must be emitted IN-BAND even though A == codecPrivate, or the A-segment decodes against the wrong entry point.
vc1_keyframe_prefix_order_seq_unchanged_entry_redefined (test)
Regression: keyframe where seq_header is UNCHANGED (stripped by scan) but entry_point is REDEFINED (changed). Before the fix, the old code appended entry_point during the scan, then reassert() appended seq_header AFTER it, producing [entry_point, seq_header] — entry_point before seq_header, violating SMPTE 421M. After the fix, assembly is always seq-then-entry.