Two tests checked only find_id(&data, ebml::REFERENCE_BLOCK).is_some().
ReferenceBlock's EBML ID is the single byte 0xFB, so that asks whether one
exists ANYWHERE in the output — not which blocks carry one. Inside a
BlockGroup, keyframe-ness is signalled by the ABSENCE of ReferenceBlock, so
"which" is the entire question.
Measured rather than assumed. A mutant emitting a ReferenceBlock on every
BlockGroup, keyframes included — which reintroduces the exact 1.6.0 defect
these tests were added for, every frame reading as a non-keyframe — passed
mvc_frame_emits_blockgroup_additional_and_reference untouched. The
duration-bearing roundtrip test did catch it, via its MkvStream read-back
rather than via the presence check. A mutant corrupting the offset VALUE
was invisible to both.
all_block_groups() parses every BlockGroup in emission order with its
Block flags, relative timestamp, duration and decoded signed ReferenceBlock.
first_block_group() now delegates to it, so there is one walker rather than
two. Both tests assert per block: the keyframe carries NO ReferenceBlock,
each non-keyframe carries one, the offset equals the distance back to the
keyframe, and the SimpleBlock-only 0x80 flag is clear throughout.
Both tests previously took muxer.writer.into_inner() WITHOUT calling
finish(), leaving cluster sizes unwritten — an unparseable file, which is
why they could only byte-scan in the first place. They now write through
SharedWriter and finish(), so the assertions run against a well-formed
Matroska file.
Verified: with the fixes in place, the every-block mutant and the
off-by-one-offset mutant both fail.
Matthew Jackson
d34979ac57