#767: import MXF (OP1a / OP-Atom) footage

Problem: the Media Browser lists .mxf files, but File > Import's dialog
filtered them out and media::is_importable refused them, although the
pinned FilmCraft codecs behind crates/media already demux MXF (AVC,
MPEG-2 / XDCAM / D-10, VC-3 / DNxHD, ProRes, PCM audio) by content.

Fix: add "mxf" to VIDEO_EXTENSIONS and to the File > Import and Set
Proxy dialog filters. Tests check MPEG-2 4:2:2 long-GOP + 24-bit PCM and
DNxHD 36 MXF against ffmpeg frames (>35 dB, measured 64-67 dB), audio
level, and that the Import dialog offers MXF. AVI stays open: FilmCraft
has no AVI demuxer.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/gaps.md

@@ -73,7 +73,7 @@ are grouped by area; the issue tracker has the rest.
 | 14 | **Object Matte** (26.2, disk cache in 26.5) | Not present; MobileSAM is already in `effectcraft-segment` and could back it | The new one-click roto; Roto Brush covers part of it | 15–30 h | G7 · [target-app-parity.md](target-app-parity.md) |
 | 15 | **Hardware video decode and encode** | No VideoToolbox, NVENC, Quick Sync or VA-API; #498 asks for it; FilmCraft has VideoToolbox / NVENC / VA-API paths to borrow | 4K playback and export speed | 25–45 h | G5/G6 · [hardware-parity.md](hardware-parity.md) |
 | 16 | **Localization depth** | Menus in 6 languages; panels in 4; effect names and ~1,650 effect parameter names untranslated; French, German, Korean, Italian, Russian (After Effects ships them) absent; #599 Hangul boxes on macOS | After Effects is used heavily in Japan, China, Korea, Brazil, Europe | 60–110 h + native review | G9 · [localization-parity.md](localization-parity.md) |
-| 17 | **Media Browser lists files import refuses** | `media_browser.rs` lists TGA, DPX, HDR, AVI, MXF; `media::is_importable` has none of them; #431 any image imports as a sequence; #324 MP3 goes silent | Confusing failures on common VFX formats (DPX, TGA) | 15–30 h | G6 · [file-format-parity.md](file-format-parity.md) |
+| 17 | **Media Browser lists files import refuses** | `media_browser.rs` lists TGA, DPX, HDR, AVI; `media::is_importable` has none of them (MXF OP1a / OP-Atom imports since #767; FilmCraft has no AVI demuxer); #431 any image imports as a sequence; #324 MP3 goes silent | Confusing failures on common VFX formats (DPX, TGA) | 15–30 h | G6 · [file-format-parity.md](file-format-parity.md) |
 | 18 | **Relative paths and relinking** | Projects store absolute footage paths; no relink when a project moves | Moving or sharing a project breaks it | 6–12 h | G4 · [file-format-parity.md](file-format-parity.md) |
 | 19 | **Plug-in ecosystem** | No After Effects SDK hosting (#600, #327 OpenFX, #334, #376 plug-in manager); our WebAssembly API has no third-party plug-ins | Many pro projects depend on Trapcode, Element, Saber… | 40–80 h for API growth; SDK hosting needs an owner decision | G8 · [scripting-parity.md](scripting-parity.md) |
 | 20 | **Multi-monitor and video output** | #486 multi-screen, floating panels on other screens, Mercury Transmit to video hardware (we have a second preview window only) | Two-screen setups are standard for professionals | 10–20 h | G2 · [hardware-parity.md](hardware-parity.md) |