CLI v0.3.0

Breaking changes

• mcap filter is now lossless by default: metadata and attachments are kept unless you pass the new --exclude-metadata / --exclude-attachments flags. The old --include-metadata / --include-attachments flags are now hidden deprecated no-ops that warn on stderr. (#1756)
• mcap filter --start / --end now apply to messages only; attachments are no longer dropped when their log_time falls outside the window (use --exclude-attachments to drop them). (#1756)
• mcap filter, mcap compress, and mcap decompress no longer silently re-sort indexed inputs: an out-of-order indexed file was previously re-sorted to log time, but the default is now --order preserve (keep stored message order). Pass --order log_time to restore the previous behavior. (#1762)
• Rewrite commands (filter, compress, decompress, sort) now write records in a standardized physical layout (metadata after the header → messages → attachments before Data End), so byte-level output can differ from 0.2.0 even when logical content is unchanged. (#1756, #1757)

New features

• Shared --order <preserve|log_time|topic> flag on filter, compress, decompress, and sort. preserve keeps stored order, log_time sorts by ascending log time (log-time alias), and topic groups each channel's messages together (channels by topic name then channel ID), placing each channel in its own chunk(s) when chunking is enabled for contiguous single-topic reads. Note that topic always buffers the selected messages in memory, and log_time buffers them when the input has no summary. (#1762, #1754, #1757)
• mcap filter gains --exclude-metadata and --exclude-attachments to opt out of the new lossless default. (#1756)
• mcap filter gains --no-chunks (write records outside of chunks). (#1763)
• mcap filter, compress, and decompress gain --no-crc (disable all output CRC fields), matching convert/merge/sort. (#1763)
• mcap sort gains an overridable --order flag (defaults to log_time), and its input and output are now optional — it reads from stdin and writes to stdout when omitted. (#1757)
• Expanded and corrected --help text across commands (remote URL inputs and --allow-remote-scan, log-time semantics for time filters, corrected cat --json encoding names, attachment retrieval, and in-place add corruption warnings), and hid the deprecated --start-nsecs / --end-nsecs flags from help (they remain accepted). (#1774)

Bug fixes

• mcap cat --json now emits protobuf fields set to their proto3 default value (e.g. 0, "", false, enum zero-variants) instead of omitting them from the output. (#1765)
• Rewrite commands no longer silently drop messages when an indexed input's Statistics record disagrees with its chunk message indexes (or a message index can't be parsed); the engine falls back to a linear scan. (#1771)
• mcap compress --compression invalid values are now rejected at parse time (exit code 2, [possible values: zstd, lz4, none]) instead of failing at runtime. (#1767)

Deprecations

These flags were renamed for consistency across the rewrite commands; the old names still work as hidden aliases that print a stderr warning, so existing invocations keep functioning.

• mcap filter --output-compression renamed to --compression, matching sort and the other rewrite commands (which already used --compression); --compression wins if both are set. (#1761)
• mcap sort --output-file renamed to --output (-o is unchanged), matching the other rewrite commands — previously only sort and merge used --output-file. filter, compress, and decompress also accept the deprecated --output-file as a hidden alias for uniformity. (#1757)
• mcap merge --output-file renamed to --output (-o is unchanged), for the same cross-command consistency. (#1771)

Performance

• Bounded memory for piped stdin: rewrite commands now spool non-seekable stdin to a temporary file and memory-map it instead of buffering the whole MCAP in memory. (#1759)
• Standardizing record placement adds an up-front metadata scan on the linear (summaryless or fallback) path, a modest throughput regression (~12–22% in benchmarks); well-formed indexed inputs are unaffected. (#1756)