Add user defined time frame or frames

[aardschok]

The user should be able to playblast a combination of small frames and frame ranges:

Example : 1-20, 25; 50; 75, 100-150
from-to, increment;

This translates to:

1. Frames 1 to 20:
2. Frames 25, 50 and 75
3. Frames 100 to 150

[BigRoy]

To elaborate a bit on this, this would be similar to printing specific pages in applications like Word as seen here:

Here's a quick function I wrote that parses it similar to how Word does it (and how V-Ray specific frame render settings supports it). Note that this supports both comma , and semicolon ; as separators.

import logging
import re

log = logging.getLogger(__name__)


def parse_frames(string):
    """Parse the resulting frames list from a frame list string.
    
    Examples
        >>> parse_frames("0-3;30")
        [0, 1, 2, 3, 30]
        >>> parse_frames("0,2,4,-10")
        [0, 2, 4, -10]
        >>> parse_frames("-10--5,-2")
        [-10, -9, -8, -7, -6, -5, -2]
    
    Args:
        string (str): The string to parse for frames.
        
    Returns:
        list: A list of frames
    
    """

    result = list()

    for raw in re.split(";|,", string):
        
        # Skip empty elements
        value = raw.strip().replace(" ", "")
        if not value:
            if raw:
                log.warning("Empty frame entry: '{0}'".format(raw))
            continue
            
        # Check for sequences (1-20) including negatives (-10--8)
        sequence = re.search("(-?[0-9]+)-(-?[0-9]+)", value)
        
        # Sequence
        if sequence:
            start, end = sequence.groups()
            frames = range(int(start), int(end) + 1)
            result.extend(frames)
            
        # Single frame
        else:
            try:
                frame = int(value)
            except ValueError:
                log.warning("Invalid frame description: '{0}'".format(value))
                continue
            result.append(frame)
            
    return result

[BigRoy]

Implemented with #25