[PYTHON] How to set the output resolution for each keyframe in Blender

2020-11-19 00_11_40-StrokesPlus.jpg

I decided to use Blender's render image for the draft of the manga. It is assumed that the render image for each key frame will be pasted into the manga creation software in correspondence with "1 frame = 1 key frame".

Normally, comic frames have different aspect ratios for each frame. However, Blender does not allow you to set the resolution for each keyframe. You have to use the same resolution for all keyframes or switch manually frame by frame. Both are inconvenient.

Therefore, I thought about how to set the resolution for each key frame. Blender allows you to set a string ** marker ** in keyframes, so I decided to record the aspect ratio of the resolution there.

In general horizontal reading manga, the vertical and horizontal size of the frame is indefinite, but this time it is a vertical reading manga, and it is assumed that the width of the frame is always constant at 2480px. The method of specifying the height and width at the same time is supplemented at the end.

Execution environment

Blender 2.90.1

Thing you want to do

screenshot.1596102429.png

I want to be able to set and hold "Scene> Dimensions> Resolution X & Y" for each keyframe.
X is fixed at 2480px, and Y wants to change according to the resolution ratio value set in the keyframe.
For example, in the image above, the aspect ratio set for keyframe 47 is 1.5, so Y = 2480 * 1.5 = 3720 px.

Realization policy

Create a Python script that "refers to the resolution ratio value set for each keyframe and automatically changes the Resolution X & Y"
Record the resolution ratio numerically on the marker

Setup steps

Enter the aspect ratio in the marker

In the Timeline panel, press M to add a marker to the keyframe and Ctrl + M to enter the aspect ratio as the marker name.

Enter the number Y / X this time. For example, X: Y = 4: 3 is 0.75, 1: 1 is 1, and 1: 2 is 2.

By the way, you can set multiple markers in one frame, but in this program, the first value found will be used as the aspect ratio.

Write a python script

Then open the Text Editor panel and enter the following code.

`set_resolution_from_marker.py`


import bpy

RESOLUTION_X = 2480
DEFAULT_RATIO = 1.0


def find_ratio_from_current_keyframe():
    #Search for the marker set for the current keyframe from all markers
    marker_items =  bpy.context.scene.timeline_markers.items()
    current = bpy.data.scenes["Scene"].frame_current
    markers = [item[0] for item in marker_items if item[1].frame == current]
    
    #Returns the default ratio if the marker does not exist
    if len(markers) < 1:
        print(f"No marker is set to current keyframe. Now ratio is {DEFAULT_RATIO}.")
        return DEFAULT_RATIO

    print("Found marker(s): ", markers)
    #Converts the marker string to a number and returns it
    for m in markers:
        try:
            ratio = float(m)
            print("Ratio is set to ", ratio)
            return ratio
        except ValueError as e:
            print(e)
            continue

    #Returns the default ratio if there are no markers that can be converted to numbers
    print(f"Marker is set to current keyframe but not valid number. Now ratio is {DEFAULT_RATIO}.")
    return DEFAULT_RATIO


def update_resolution(scene):
    scene.render.resolution_x = RESOLUTION_X
    scene.render.resolution_y = RESOLUTION_X * find_ratio_from_current_keyframe()
    

#Set callback to update resolution when changing keyframes
bpy.app.handlers.frame_change_pre.append(update_resolution)

ℹ️ Brief commentary

Since there was no API to "get only the markers in the current keyframe", we get all the markers in the entire timeline once and extract only the markers in the current keyframe from them.
If no marker is set in the current keyframe or no valid number is entered, the constant DEFAULT_RATIO is returned. This time it is 1 (= aspect ratio 1: 1).
The last line sets the callback to call update_resolution () every time a keyframe changes to change the resolution.
Reference: Application Handlers \ (bpy \ .app \ .handlers ) — Blender Python API

Run the script

Run "Run Script (Alt + P)" in the Text Editor panel.

After that, Resolution X & Y is set automatically every time you switch keyframes.

Supplement

What if I want to be able to set both Resolution X & Y?

This time it was a slightly special case of "X = 2480px fixed", but if you want to set X and Y at the same time, you can easily handle it by changing the marker notation and Python script.

For example, write 1280,720 in the marker, split the string with commas in a Python script, and assign the first value to X and the second value to Y.

Can't it be realized with a driver?

I could not do it. This is because the driver cannot set any of the values under the Scene property, including Resolution.

Why doesn't the resolution update when I enter or change a marker?

I couldn't find a callback that could be called at that time: disappointed: Sorry for your inconvenience, but please advance the keyframe by one with the arrow keys and move it back.