Video editing and tracking

The execution model is in blender-core. Rendering the 3D shots and the compositor (5.0 API) are in blender-rendering.

One call each

scripts/vse_edit.py -- --clips //renders/sh010/ //renders/sh020/ //logo.png --crossfade 12 --title "Project" --audio //music.wav --out //edit.mp4 --render
scripts/vse_edit.py -- --clips a.mp4 b.mp4 c.mp4 --crossfade 0 --fps 24 --out //review/f_#### --render   # hard cuts to PNG

import track_camera; print(track_camera.run(clip="C:/shots/sh010.mp4", focal=35, sensor=36))  # live/MCP only

vse_edit.py

• Builds into its own Edit scene (--scene), so 3D scenes stay untouched. Clips go on alternating channels 1/2, crossfades (CROSS) on 3, the title on 4, clip audio on 6/7 (movies get their sound strip), and music on 8 (trimmed to the edit with a --audio-fade volume fade-out).
• A clip may be a movie, a still (--still-seconds), a folder of frames, or a #### pattern. Each crossfade overlaps the previous clip by --crossfade frames, so the edit gets shorter by that much per cut. Re-running replaces the previous edit.
• Sets view transform Standard: footage must pass through untouched (measured: AgX turned pure red into 0.86/0.23/0.13). Grade on purpose with strip modifiers instead.
• Output: .mp4/.mov/.mkv = H.264 (CRF high, preset good) + AAC 192k stereo. Any other path = PNG frames. 5.0+ needs image_settings.media_type = "VIDEO" before file_format = "FFMPEG". It reports the file size, and the test decodes it back (frame count, size).

Editing rules pros follow

• Match the frame rate first (--fps = the footage/render rate). Mixed rates drift audio. Re-render or retime (SPEED effect) instead.
• Heavy footage: build proxies (strip.use_proxy = True, 25/50%, sequencer.rebuild_proxy). 5.2 builds only proxies (no .blen_tc timecode files anymore).
• Per-strip color: strip.colorspace_settings.name (sRGB for 8-bit video, Linear Rec.709 for EXR renders). A dedicated edit scene keeps 3D color settings out of the edit.
• 5.2 API: strips.new_movie(..., stream=N) / new_sound(stream=N) pick a stream from multi-track files. strip.connections lists connected strips. New effect type COMPOSITOR (a node-tree effect). Text strips have Subtitles / Main Title / Corner Title presets in the UI. Timing uses left_handle/right_handle/duration (5.1 names). Strip keyframes live on the scene's action.

Motion tracking (track_camera.py, live session)

• The Clip Editor operators need a window, so this borrows the largest area, runs, and restores it. In -b it raises. It detects features at the first and last frame, tracks both ways, deletes tracks shorter than min_frames, solves (auto keyframes, refines focal only if unknown), deletes tracks above max_error px and re-solves, then runs setup_tracking_scene (camera + Camera Solver constraint, background footage, frame range).
• Measured on a synthetic 40-frame dolly at 960×540: 56 tracks, 0.19 px solve error, 35 mm focal kept exactly. Quality bar: < 0.3 px great, < 0.5 good, > 1 px slides.
• Give focal/sensor whenever known. The solver is far more stable than when refining the focal. Set the sensor before the focal (focal is stored in px).
• Nodal pans (camera only rotates): tripod=True. A normal solve fails without parallax.
• Orient the scene after solving (UI, Clip Editor context): select 3 floor tracks → clip.set_plane(plane="FLOOR"), 1 track → clip.set_origin(), 2 tracks a known distance apart → clip.set_scale(distance=…). Otherwise scale and up are arbitrary.
• Other jobs: screen/sign replacement → clip.create_plane_track() on 4+ tracks of a planar surface. Shaky footage → 2D stabilization (tracking.stabilization.use_2d_stabilization, add tracks). Points for modeling → clip.bundles_to_mesh().

Shooting/footage tips that make solves work

Fast shutter (little motion blur), real parallax (move the camera, don't just pan), textured static surfaces at several depths, no rolling-shutter whip pans, and a lens grid shot to calibrate distortion when using wide lenses.

Gotchas

• bpy.ops.render.render(animation=True) renders the sequencer only when scene.render.use_sequencer is on and the strips are in the scene being rendered. The script renders its own edit scene.
• Removing a clip also removes its effect strips. Collect names before deleting in loops.
• Image sequences must be contiguous. Missing frames show as black.