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YouTube Splitter                                                

Recently I found a YouTube exclusive music mix which I wanted to
have locally. Commonly I use  youtube-dl  to download stuff from
that site  which is usually the top pick for this task if paired
with FFmpeg assuming both of their executables are in the system
%PATH% (I hope you know what that means).                       

However,  youtube-dl can not make FFmpeg to split the content by
chapters. I also tried to find a viable solution on the internet
without success. Finally, I wrote the following Python script to
get the thing done.                                             

Once splitted, I used the great Mp3tag software for the tagging.

--[ youtubesplitter.py ]================================================================------------------------

"""                                                                                                             
youtubesplitter.py                                                                                              
2021 Szieberth Ádám - Public Domain                                                                             

This script splits a downloaded YouTube media file by its chapters.                                             

Usage:                                                                                                          
python youtubesplitter.py <myyoutubemediafile>                                                                  

Hint: call youtube-dl with the `--write-info-json` option previously.                                           

Notes:                                                                                                          
* If you have the media file downloaded already you can prevent its re-download                                 
  with the `--skip-download` youtube-dl option.                                                                 

* FFmpeg executable is assumed to be in your %PATH%.                                                            
"""                                                                                                             

import json                                                                                                     
import os                                                                                                       
import pathlib                                                                                                  
import re                                                                                                       
import sys                                                                                                      

filename_replaces = {                                                                                           
    "<":  "_lessthan_",                                                                                         
    ">":  "_greaterthan_",                                                                                      
    ":":  "_colon_",                                                                                            
    '"':  "_doublequote_",                                                                                      
    "/":  "_forthslash_",                                                                                       
    "\\": "_backslash_",                                                                                        
    "|":  "_bar_",                                                                                              
    "?":  "_questionmark_",                                                                                     
    "*":  "_star_",                                                                                             
}                                                                                                               

if __name__ == "__main__":                                                                                      

    if len(sys.argv) < 2:                                                                                       
        print(f'ERROR! Path of media file is assumed as first argument.')                                       
        print(__doc__)                                                                                          
        sys.exit(1)                                                                                             

    p = pathlib.Path(sys.argv[1]).resolve()                                                                     

    if not p.is_file():                                                                                         
        print(f'ERROR! Incorrect path.')                                                                        
        print(__doc__)                                                                                          
        sys.exit(2)                                                                                             

    pext = p.suffix.lstrip(".")                                                                                 

    pj = p.parent / f'{p.stem}.info.json'                                                                       

    if not pj.is_file():                                                                                        
        print(f'ERROR! Missing Info JSON.\nExpected the following file: "{pj}"')                                
        print(__doc__)                                                                                          
        sys.exit(3)                                                                                             

    with pj.open("r", encoding="utf-8") as f:                                                                   
        info = json.load(f)                                                                                     

    chapters = info.get("chapters", [])                                                                         

    for nr, c in enumerate(chapters, 1):                                                                        
        title = c["title"]                                                                                      
        nrm = re.search('^\d+\.?\s+', title)                                                                    
        if nrm:                                                                                                 
            nrstr = nrm.group(0).rstrip()                                                                       
            nr = int(nrstr.rstrip("."))                                                                         
            title = title[nrm.end():]                                                                           
        else:                                                                                                   
            nrstr = f'{nr}.'                                                                                    
        po = pathlib.Path("".join(filename_replaces.get(c, c) for c in f'{nr:0>2} {title}.{pext}'))             
        command = f'ffmpeg -i "{p}" -ss {c["start_time"]} -to {c["end_time"]} -c copy "{po}"'                   
        print("\n" * (1 if 1<nr else 0) + command, end="\n\n")                                                  
        os.system(command)                                                                                      

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