Video Sequence Editor in Python

Trigger

Use this skill when the user:

• Builds or inspects a VSE / sequencer timeline from a script
• Mentions sequence_editor, strips, sequences, new_effect, COLOR strips, or StripTransform
• Hits AttributeError: 'SequenceEditor' object has no attribute 'sequences' on 5.x
• Hits TypeError on new_effect kwargs (frame_end vs length)
• Renders a sequencer composite whose COLOR cells ignore transform.scale_* after a resolution change

High-level shape

import bpy

scene = bpy.context.scene
se = scene.sequence_editor or scene.sequence_editor_create()
coll = se.strips if hasattr(se, "strips") else se.sequences

if bpy.app.version >= (5, 0, 0):
    strip = coll.new_effect(
        name="A", type="COLOR", channel=1,
        frame_start=1, length=10,
    )
else:
    strip = coll.new_effect(
        name="A", type="COLOR", channel=1,
        frame_start=1, frame_end=11,
    )
strip.color = (0.85, 0.10, 0.22)

Branch on bpy.app.version, never on bpy.app.version_string. An empty bpy_prop_collection is falsy — se.strips or se.sequences silently falls through to the legacy accessor on an empty timeline. Always branch on hasattr.

Accessor: .strips vs .sequences

	4.5 LTS	5.1 / 5.2+
Canonical collection	.strips (.sequences is a bridge to the same strips)	.strips only
.sequences	Present, same contents as .strips	AttributeError

def strips_coll(se):
    return se.strips if hasattr(se, "strips") else se.sequences

Do not write se.sequences in new code. On 5.x it is gone; on 4.5 .strips already exists.

new_effect end kwarg

strips.new_effect(...) ends a strip with one accepted end argument. The other raises TypeError.

span = (1, 33)  # end-exclusive [start, end)

if bpy.app.version >= (5, 0, 0):
    strip = coll.new_effect(
        name="A", type="COLOR", channel=1,
        frame_start=span[0], length=span[1] - span[0],
    )
else:
    strip = coll.new_effect(
        name="A", type="COLOR", channel=1,
        frame_start=span[0], frame_end=span[1],
    )

Timeline bounds: frame_final_start / frame_final_end / frame_final_duration on 4.5. On 5.x those names are deprecated aliases (removal announced for 6.0); canonical accessors are left_handle / right_handle / duration. Scene strips take four args — new_scene(name, scene, channel, frame_start) — with no length / frame_end kwarg on either version.

The TRANSFORM effect type is removed on 5.x. Place strips with per-strip strip.transform (StripTransform) on both versions. Effect inputs are input_1 / input_2 (creation kwargs input1 / input2).

COLOR strip intrinsic size (5.2)

4.5 LTS and 5.1 COLOR strips have no intrinsic size. transform.scale_* is a fraction of the output frame. Creating at factory resolution then rendering a tiny buffer is fine.

5.2 and later bake readonly width / height from scene render resolution at new_effect time. Scale and offset are then in that media space, not a later output size. Set scene resolution before building strips.

This split is not in the 5.2 python_api release notes. Witnessed by examples/vse-cut-list/ --check-pixels.

width, height = 96, 54
scene.render.resolution_x = width
scene.render.resolution_y = height

se = scene.sequence_editor or scene.sequence_editor_create()
coll = se.strips if hasattr(se, "strips") else se.sequences

if bpy.app.version >= (5, 0, 0):
    strip = coll.new_effect(
        name="A", type="COLOR", channel=1,
        frame_start=1, length=10,
    )
else:
    strip = coll.new_effect(
        name="A", type="COLOR", channel=1,
        frame_start=1, frame_end=11,
    )

if bpy.app.version >= (5, 2, 0):
    # 5.2+: readonly width/height baked at new_effect from scene.render
    assert (strip.width, strip.height) == (width, height)
    # strip.width = 64  # TypeError — readonly
else:
    # 4.5 / 5.1: no intrinsic size; hasattr(strip, "width") is False
    pass

strip.transform.scale_x = 0.36
strip.transform.scale_y = 0.36

Creating at factory 1920×1080 then dropping the scene to 96×54 for a check render makes a 0.36-scaled COLOR cell larger than the output. On 5.2 the long-runner covers the frame; pixel samples read the wrong strip.

A lone COLOR strip does honor transform.scale_* on 5.2. The break is media size vs a later output size, not "transform is ignored."

Common AI mistakes

1. sequence_editor.sequences on 5.x. AttributeError. Use .strips (with hasattr only as a 4.5 bridge).

2. Wrong new_effect end kwarg. frame_end= on 5.x and length= on 4.5 both raise TypeError.

3. Creating COLOR strips, then changing render size (the 5.2 trap):

   a = coll.new_effect(...)          # bakes 1920×1080 on 5.2
   scene.render.resolution_x = 96    # output changed; media size did not

   Set scene.render.resolution_* before new_effect.

4. se.strips or se.sequences. An empty collection is falsy, so this falls through to .sequences on a fresh editor.

5. TRANSFORM effect type on 5.x. Gone. Use strip.transform.

6. Scene strip pointing at its own scene. Feedback loop; renders transparent. Source a separate scene.

7. Effect strips consume their inputs only when stacked on a channel above those inputs. Below, the inputs keep compositing independently. A GAMMA_CROSS asked to outlast its inputs' overlap is silently clamped to the overlap.

See also

• Example examples/vse-cut-list/ — accessor rename, new_effect kwargs, save/reload, and the 5.2 COLOR size bake (--check-pixels asserts A.width, A.height == render size on 5.2+).
• Example examples/vse-gamma-cross/ — GAMMA_CROSS blend curve.
• Audit log: docs/technical-audit.md § Findings the release notes did not list.

References

• bpy.types.SequenceEditor: https://docs.blender.org/api/current/bpy.types.SequenceEditor.html
• bpy.types.Sequence: https://docs.blender.org/api/current/bpy.types.Sequence.html
• 4.5 LTS SequenceEditor: https://docs.blender.org/api/4.5/bpy.types.SequenceEditor.html
• 5.1 SequenceEditor: https://docs.blender.org/api/5.1/bpy.types.SequenceEditor.html