Python scripting - append frame directly to video

Question

I have a script that modifies position and rotation of some objects as well as individual verticies. For each frame I render PNG and then I insert them to video sequence to render the final video. The problem is that I have 6000 frames and the individual image files are quite large. Is there a way to append the frames as they are created in the for loop to single video file? As I understand it I can't keyframe individual verticies and therefore can't create only keyframes in the for loop and render the video afterwards

Here is the code:

import bpy
import csv

FILE = 'Data/20200712.csv'
OUTPUT = 'Other/Output/'

#
fp = bpy.context.scene.render.filepath # get existing output path
bpy.context.scene.render.image_settings.file_format = 'PNG' # set output format to .png

arrow = bpy.data.objects['Arrow']
target = bpy.data.objects['Target']

#find which vertex of pyramid is moving
bottom = bpy.data.objects['Cover']
for i, vert in enumerate(bottom.data.vertices):
    if vert.co[2]>0.5:
        ind = i

with open(filename, newline='') as data:
    reader = csv.DictReader(data)
    counter = 0
    for row in reader:
        if row['A'] is not None:
            frame_num = int(row['SampleTime'])
            
            x = float(row['hB'])            #load value saved as hB
                    
            y = float(row['hA'])            #load value saved as hA
            
            arrow.rotation_euler = (-y/3, x/3, 0)
            
            target.location = (row['gestTarget0'], row['gestTarget1'], 0.9)
            
            bottom.data.vertices[ind].co[0] = x/5
            bottom.data.vertices[ind].co[1] = y/5
            
            bpy.context.scene.frame_set(frame_num)
            #arrow.keyframe_insert(data_path="location", frame=frame_num)
            arrow.keyframe_insert(data_path='rotation_euler', frame=frame_num)
            
            target.keyframe_insert(data_path="location", frame=frame_num)
            
            bpy.context.scene.frame_current = frame_num
            bpy.context.scene.render.filepath = OUTPUT + str(frame_num)
            bpy.ops.render.render(write_still=True) # render still
            
#        counter += 1
#        
#        if counter>200:
#            break

bpy.context.scene.render.filepath = fp #restore filepath
```

Answer 1

Not sure if handler make your requirement but I thought this should work:

1. Collect your data into a list or dict(I use dict)
2. According to the scene.current_frame, set the corresponding value to those object in data.
3. Make the process a handler and register it to bpy.app
4. Render your animation normally using video format

import bpy
import csv

FILE = filename = 'T:/data.csv'
OUTPUT = 'Other/Output/'

arrow = bpy.data.objects['Arrow']
target = bpy.data.objects['Target']
bottom = bpy.data.objects['Cover']  # find which vertex of pyramid is moving

ind = -1
for i, vert in enumerate(bottom.data.vertices):
    if vert.co[2] > 0.5:
        ind = i
        break  # Should be break here?
assert ind != -1, "Should find a vertice index here."

with open(filename, newline='') as data:  # Is filename defined before?
    reader = csv.DictReader(data)
    counter = 0
    # Create a dictionary, key is the frame number.
    data_frame = {
        int(row['SampleTime']): {
            'x': float(row['hB']),
            'y': float(row['hA']),
            'arrow.rot': (-float(row['hA']) / 3, float(row['hB']) / 3, 0),
            'target.loc': (float(row['gestTarget0']), float(row['gestTarget1']), 0.9)
        }
        for row in reader
        if row.get('A', None) is not None
    }

def obj_handler(scene):
    fn = scene.frame_current
    try:
        arrow.rotation_euler = data_frame[fn]['arrow.rot']
        target.location = data_frame[fn]['target.loc']
        bottom.data.vertices[ind].co.x = data_frame[fn]['x'] / 5
        bottom.data.vertices[ind].co.y = data_frame[fn]['y'] / 5
    except KeyError:
        print(f"Frame number ({fn}) is not in Sample Time.")
        pass
    except:
        raise

bpy.app.handlers.frame_change_pre.append(obj_handler)

# Render Animation

The data used:

The scene move correctly according to data fed:

Answer 2

By default blender don't allow to animate in editmode(i.e keyframing vertices properties). So to over come this problem you need to enable AnimAll addon at "preference->addon -> AnimAll". This creates a new tab in right side panel of "3d port view". Go-to this panel unmark select only check box and Mark points check box. Hope this help you.