Import: Interpret Footage has Start Timecode, as in After Effects (#297)

After Effects' Interpret Footage has Start Timecode: Use Source File
Timecode, or Override Start, which changes the timecode the footage
shows and leaves its frames alone. The Start Frame field that trimmed or
padded a sequence's head isn't in After Effects, so it is replaced.

Footage.start_timecode (Override Start, in frames at the footage's
rate; None = Use Source, 0 as file timecode isn't read) relabels source
time: the Footage panel's current time and footage.info's `timecode`
count from it. file.interpretFootage takes `overrideStart` and
`startTimecode` (timecode, read at the footage's rate after any frame
rate change, or a frame number, 0 to 1e9). It applies to every footage
with time, not only sequences, and Reload keeps it. A sequence's frames
always run from its first file's number to its last.

Test: start_timecode_only_relabels_source_time (project),
interpret_footage_start_timecode_relabels_source_time (engine: the
reply, the Footage panel's timecode, frame numbers, Use Source, the
footage's rate, bad values, undo), Reload keeps it, and the Interpret
Footage fields in ui_drag_drop.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/agents.md

@@ -210,7 +210,7 @@ build real projects through these interfaces; they are worked examples of everyt
   `"sequence": false`: one still; `"alphabetical": true`: Force Alphabetical Order, the files
   play one after another) at `frameRate` or 30 fps (Settings ▸ Import). Missing frames show
   colour bars, as in After Effects. `file.interpretFootage {"items":[id], "frameRate":12,
-  "startFrame":1001}` conforms them (the item and layers that ran to its end get the new
+  "startTimecode":1001}` conforms them and sets Override Start (the item and layers that ran to its end get the new
   length). See [footage.md](footage.md).
 * **Multi-layer OpenEXR**: `layer.channels {layer}` lists a footage layer's EXR layers and
   channels (`{"layers":[{"name":"diffuse","rgba":["diffuse.R","diffuse.G","diffuse.B",""]}]}`);

docs/footage.md

@@ -61,7 +61,7 @@ used, and layers that ran to the end of the footage keep doing so.
 |---|---|
 | **Alpha** | *Straight - Unmatted*, *Premultiplied - Matted With Color* (with the matte colour), *Ignore* (opaque), or *Guess* (EffectCraft looks at the first frame). *Invert Alpha* flips it. |
 | **Assume this frame rate** | The rate the frames play at. A 250-frame sequence at 25 fps lasts 10 seconds; at 24 fps, 10.4 seconds. |
-| **Start Frame** (sequences) | The frame number at the footage's first frame. It defaults to the first file's number. A higher number trims the head (start a 1001–1250 render at 1010); a lower one adds placeholder frames before the first file. |
+| **Start Timecode** | *Use Source File Timecode* (0:00:00:00), or *Override Start*: the timecode the footage's first frame shows in the Footage panel. It relabels source time only; the frames stay the same. For a 1001–1250 render at 24 fps, Override Start 0:00:41:17 (frame 1001) makes source time count from the render's own frame numbers. |
 | Fields, pixel aspect, loop, colour profile, linear light | As in After Effects. |
 
 Settings ▸ Import ▸ **Report Missing Frames** (on by default) lists the missing frame numbers
@@ -71,7 +71,8 @@ when a sequence imports; Interpret Footage lists them too.
 fields, pixel aspect, loop and colour settings to other footage.
 
 Agents: `file.interpretFootage {"items": [id], "frameRate": 24, "alpha": "premultiplied",
-"startFrame": 1001}` (`"startFrame": "file"` goes back to the first file's number).
+"startTimecode": 1001}` (timecode or a frame number; `"overrideStart": false` goes back to Use
+Source File Timecode).
 
 ## Replacing and reloading
 

docs/parity.md

@@ -172,7 +172,7 @@ the disk cache in the formats wave; the 3D Camera Tracker in M12.6.)
 | 3D | 88% | 5.5 | reflections of other layers (Advanced 3D surfaces reflect only the Environment light; Material Options ▸ Appears in Reflections is stored but has no visible effect yet, #261), multi-view layouts, the Extended Viewer for Advanced 3D comps (Classic 3D Extended Viewer landed in M13.5 UI completion); collapsed precomps of another size seen through the parent's camera render (fixed in M13.2); stereo rigs, orbit nulls, lights controlled by the camera, cameras/lights from glTF models, environment backgrounds, Advanced 3D motion blur, blend modes and track mattes landed in M7.7; Classic 3D iris-shaped bokeh with highlights, progressive depth of field on tilted layers and the focus-link commands landed in M13.5; Advanced 3D depth of field with the iris and highlight options, collapsed precomps as real Advanced 3D geometry and extruded text/shape strokes landed in M13.8; Advanced 3D (glTF/OBJ models, primitives, extruded text and shapes, PBR, image-based light, shadow maps, GPU rasteriser) in M7.4–M7.6; Advanced 3D end to end on the GPU (motion blur, iris depth of field, compositing) in M13.11 |
 | Effects | ≈ 85% | 3.0 | GPU versions of the remaining effects (280 run on the GPU since M13.29, EFF-5: M13.28 added the remaining pixel effects and the geometry and audio generators (Lightning, Advanced Lightning, Beam, Lens Flare, Radio Waves, Vegas, Stroke, Scribble, Write-on, Paint Bucket, Eyedropper Fill, CC Glue Gun, CC Threads, Audio Spectrum / Waveform, Basic / Path Text); M13.29 added the particle effects (CC Particle World / Systems II, Particle Playground, CC Ball Action, CC Pixel Polly, CC Scatterize, Curl Noise) and removed the fallbacks of Shatter's wireframe views, Foam's extras, Timewarp's Matte Layer, strong Warp Fisheye / Twist bends and custom `.ocio` configs; M13.23 added the 3D Channel and Immersive Video families, Apply Color LUT, the OCIO effects, Color Profile Converter and the simulations' render passes (Card Wipe included); M13.22 added the CC light family, the CC transitions, Block Dissolve, Radial Shadow, CC Bender / Blobbylize / Cylinder / Sphere / Spotlight / Environment, 3D Glasses, Numbers, Timecode and the time effects joined the 166 of M13.13; Fractal and the analysis / tool effects still render on the CPU) and the missing controls listed as partial in [effects.md](effects.md) (every After Effects effect exists since M9.11, M12.5 and M12.6; parameter names, order, twirl-downs, popups, units and defaults were aligned in M9.12) |
 | Interface | 75% | 5.0 | more Learn tutorials and pixel-level fidelity of dialogs (G2 on 9 October: the in-window menu bar works from the keyboard (Alt, arrows, Enter, Escape) and the app's shortcuts wait while a menu is open, #279; the Timeline's composition marker bin and numpad * add comp markers, #275; Settings ▸ Appearance ▸ UI Scale (75–200 %, beyond After Effects, which follows the system's scaling), #284; G2 on 7 October: Project items, files and effects dropped on the Composition viewer, Project items dropped in the Timeline between layers and at a time, #85, #88, #89; popup menus moved to fit the window take clicks, so Render Queue templates apply, #117; View ▸ New Viewer landed in M13.32; an automation id on every control of Composition and Solid Settings, Group / Ungroup Shapes in the Layer menu, Window ▸ Learn, the flowchart shortcuts and Reveal in Explorer landed in M3.10 and M3.13; the Home ▸ Templates gallery (eight original built-in templates, user templates from File ▸ Save as Template…) and View ▸ Simulate Output ▸ My Custom RGB… landed in M13.25; Timeline layer reordering by drag, a non-snapping viewer pan, a working rename field and twirl arrows, and the full set of property reveal shortcuts — double presses, Alt+Shift keyframes, Ctrl+` — landed in M13.17–M13.20; the Home ▸ Learn tab with interactive tutorials and a UI fidelity pass landed in M13.5 UI completion; visual editors for Lumetri RGB / hue-saturation curves, Colorama's output cycle wheel, Glow's colour map and Reshape's correspondence points (viewer handles), a scrolling Preview panel and AE-style Composition / Timeline tabs (close, label swatch, viewer lock) landed in M13.10; Timeline outline and Project panel columns scroll horizontally, the Layer Style dialog, ROI resize handles, Pan Behind snapping and 3D Reference Axes landed in M13.5; native macOS menu bar, Timeline columns/search/reveal-add, Home screen with recent projects and all AE workspaces landed; viewer rulers/snapping/channels/snapshots landed in M0.13) |
-| Project | ≈ 68% | 5.5 | OCIO displays beyond the built-in tone map; relative footage paths and relinking when a project moves (unsaved-changes prompts, a modified mark that follows undo and project files that name their version and always reopen landed in M3.9 and M3.14; auto-save and crash recovery in M3.7; Color Engine with OCIO/ACES working spaces, HDR compand/tone mapping, Rec. 2100 PQ/HLG output, Feet + Frames, display colour management, Simulate Output and the locked viewer landed in M7.7; proxies and Interpret Footage fields / pixel aspect / alpha guess landed: PRJ-8, PRJ-3; image sequence import options (Sequence, Force Alphabetical Order, frame rate, picked ranges, folders, the browser), missing-frame placeholders and Interpret Footage Start Frame landed: #297) |
+| Project | ≈ 68% | 5.5 | OCIO displays beyond the built-in tone map; relative footage paths and relinking when a project moves (unsaved-changes prompts, a modified mark that follows undo and project files that name their version and always reopen landed in M3.9 and M3.14; auto-save and crash recovery in M3.7; Color Engine with OCIO/ACES working spaces, HDR compand/tone mapping, Rec. 2100 PQ/HLG output, Feet + Frames, display colour management, Simulate Output and the locked viewer landed in M7.7; proxies and Interpret Footage fields / pixel aspect / alpha guess landed: PRJ-8, PRJ-3; image sequence import options (Sequence, Force Alphabetical Order, frame rate, picked ranges, folders, the browser), missing-frame placeholders and Interpret Footage Start Timecode landed: #297) |
 | Masks & roto | 74% | 5.0 | (audit estimates; Roto Brush 2.0 / 3.0's trained model, MobileSAM in the swappable `segment` module, has since landed in M13.35; variable-width mask feather points with the Mask Feather tool landed in M13.5; mask tracking and Mask Interpolation landed in M6.6; Roto Brush & Refine Edge with graph-cut segmentation, flow propagation, edge matting, decontamination and Freeze in M6.7) |
 | Preview | 77% | 2.8 | GPU effects for the audio-driven effects and the stepped particle systems; content-keyed RAM preview frames (an edit drops every comp's), audio scrubbing, more snapshot slots (G2 on 7 October: Audio, Lock and Shy switches keep the cached frames and playback with audio waits for frames instead of skipping them, #103; running out of video memory renders the frame on the CPU and keeps fewer GPU frames instead of crashing, #106; RAM preview keys with the render options, least-recently-shown eviction, Auto resolution while playing, Cache Before Playback that fits, an achieved-fps readout, Cache Frames When Idle and purges that clear what they name landed in M4.5–M4.8; 3D channel, VR, OCIO, Card Wipe and the simulations' render passes run on the GPU since M13.23; Advanced 3D layers with blend modes / track mattes / Preserve Transparency and environment backgrounds composite on the GPU since M13.22; pooled GPU textures and fused quantisation since M13.13: Lower Third GPU warm 21 → 4 ms/frame, and Auto now picks the CPU or the GPU per comp from measured frame times; Advanced 3D runs — raster, motion blur, iris depth of field, compositing — and wireframes run on the GPU since M13.11: CPU warm 3394 → GPU warm 290 ms/frame at 1920×1080 (11.7×; Half 968 → 85 ms), GPU ≠ CPU on 0.005 % of pixels, on an M4 Pro under load; Classic 3D bokeh depth of field — iris shapes, highlights, fringe, progressive blur on tilted planes — runs in WGSL since M13.6: 3D Showcase GPU warm 205 → 54 ms/frame at full size on an M4 Pro; the Preview panel's five shortcuts with their own Include / Loop / Cache Before Playback / Range / Play From / Frame Rate / Skip / Resolution / Full Screen / stop options and `playback.settings.get/set` landed in M13.8; Classic 3D runs and adjustment layers composite on the GPU since M12.7; persistent disk cache with the blue cache bar landed; region of interest, snapshots, exposure and Fast Previews landed in M0.13) |
 | Tracking | ≈ 96% | 0.3 | face tracking's trained model (MediaPipe Face Landmarker, M13.36) is an optional download; without it the classical (skin model + feature components + shape model) fitter is weak on profile views and occluded faces; Rolling Shutter Ripple is approximated by Subspace Warp's mesh density (face tracking (Outline Only / Detailed Features with Face Track Points and Extract & Copy Face Measurements), Subspace Warp's content-preserving mesh warp on subspace-smoothed trajectories, and radial lens distortion (k1, k2) in the camera bundle adjustment with Undistort Footage landed in M13.3; Rolling Shutter Repair in M9.11; point tracker, mask tracking, Warp Stabilizer and the 3D Camera Tracker in M6.x / M12.5 / M12.6) |