Honest PictureInfo population for HEVC, on the same principle as H.264.
- Consolidate the bit reader: hevc.rs had its own BitReader (used by the SPS
parser); h264 just gained one in startcode. Promote startcode's to the single
shared pub(crate) reader (adds read_bits) and delete hevc's copy — one proven
primitive, reused (SPS parse + both slice-type decoders).
- hevc: decode slice_type from the first coded slice's slice_segment_header
(H.265 §7.3.6.1) → I/P/B (§7.4.7.1). The offset to slice_type depends on
num_extra_slice_header_bits, which lives in the PPS — so we parse it from the
ACTIVE PPS (§7.3.2.3) and only measure slice_type when that PPS is known.
With no active PPS we decline rather than guess: coding stays None, honestly
absent. Set coding = coding_type_only(...) and source = pes.source; field
order (pic_struct SEI) is not decoded, so field_order() is honestly None.
- Tests: I/P/B from real slice headers, source carry, field-order absence, and
the no-PPS honest-omission case.
Matthew Jackson
6acc26a802