scripts/transcode.py

# /// script
# requires-python = ">=3.13"
# dependencies = [
#     "ffmpeg",
#     "watchdog",
# ]
# ///
import argparse
import time
import sys
import subprocess
import os
from pathlib import Path
from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler

# Supported video extensions to monitor
VIDEO_EXTENSIONS = {'.mkv', '.mp4', '.avi', '.mov', '.wmv', '.flv', '.webm', '.m4v', '.ts'}

def get_ffmpeg_command(input_path, output_path):
    """
    Constructs the FFmpeg command based on the Handbrake preset requirements.
    """
    return [
        "ffmpeg",
        "-n",                  # Never overwrite output files (extra safety)
        "-i", str(input_path), # Input file
        "-c:v", "av1_nvenc",   # Video Encoder
        "-pix_fmt", "p010le",  # 10-bit color
        "-preset", "p4",       # Medium preset
        "-rc", "vbr",          # Variable Bit Rate control
        "-cq", "35",           # Constant Quality factor
        # Filter chain: Deinterlace -> Scale down if >1080p -> Cap FPS at 30
        "-vf", "yadif,scale='min(1920,iw)':-2,fps=30",
        "-c:a", "aac",         # Audio Encoder
        "-b:a", "160k",        # Audio Bitrate
        "-ac", "2",            # Audio Channels (Stereo)
        "-color_range", "tv",  # Limited color range
        "-movflags", "+faststart", # Web optimization
        str(output_path)       # Output file
    ]

def transcode_file(input_file, output_file):
    input_path = Path(input_file)
    output_path = Path(output_file)

    # 1. Check existence logic
    if output_path.exists():
        print(f"[SKIP] Output file already exists: {output_path.name}")
        return

    # 2. Check if file is ready (simple size stability check)
    # This prevents transcoding files that are still being copied into the folder
    print(f"[WAIT] Ensuring file is ready: {input_path.name}...")
    try:
        historical_size = -1
        while True:
            current_size = input_path.stat().st_size
            if current_size == historical_size and current_size > 0:
                break
            historical_size = current_size
            time.sleep(2) # Wait 2 seconds between checks
    except FileNotFoundError:
        return # File was deleted before we could process it

    print(f"[START] Transcoding: {input_path.name} -> {output_path.name}")
    
    cmd = get_ffmpeg_command(input_path, output_path)
    
    try:
        # Run FFmpeg
        subprocess.run(cmd, check=True)
        print(f"[DONE] Successfully created: {output_path.name}")
    except subprocess.CalledProcessError as e:
        print(f"[ERROR] FFmpeg failed for {input_path.name}")
    except KeyboardInterrupt:
        print("\n[STOP] Interrupted by user.")
        sys.exit(0)

class NewFileHandler(FileSystemEventHandler):
    def __init__(self, output_dir):
        self.output_dir = Path(output_dir)

    def on_created(self, event):
        if event.is_directory:
            return
        self.process(event.src_path)

    def on_moved(self, event):
        if event.is_directory:
            return
        self.process(event.dest_path)

    def process(self, file_path_str):
        input_path = Path(file_path_str)
        
        # Filter for video extensions
        if input_path.suffix.lower() not in VIDEO_EXTENSIONS:
            return

        # Determine output path
        # We rename the file to avoid conflicts if input/output dirs are same (though not recommended)
        new_filename = input_path.stem + ".mp4"
        output_path = self.output_dir / new_filename

        transcode_file(input_path, output_path)

def main():
    parser = argparse.ArgumentParser(description="Nvidia AV1 Transcoder & Watcher")
    
    # Mutually exclusive group for modes
    group = parser.add_mutually_exclusive_group(required=True)
    group.add_argument("--input", type=str, help="Single file to transcode")
    group.add_argument("--watch-dir", type=str, help="Directory to monitor for new files")

    parser.add_argument("--output-dir", type=str, help="Output directory (Required for --watch-dir)")

    args = parser.parse_args()

    # --- Mode 1: Single File ---
    if args.input:
        input_path = Path(args.input)
        if not input_path.exists():
            print(f"Error: Input file '{args.input}' not found.")
            sys.exit(1)
        
        # If output dir provided, use it. Otherwise use source folder + _av1 suffix
        if args.output_dir:
            out_dir = Path(args.output_dir)
            out_dir.mkdir(parents=True, exist_ok=True)
            output_path = out_dir / (input_path.stem + ".mp4")
        else:
            output_path = input_path.parent / (input_path.stem + "_av1.mp4")

        transcode_file(input_path, output_path)

    # --- Mode 2: Watch Directory ---
    elif args.watch_dir:
        if not args.output_dir:
            print("Error: --output-dir is required when using --watch-dir")
            sys.exit(1)

        watch_dir = Path(args.watch_dir)
        output_dir = Path(args.output_dir)

        if not watch_dir.exists():
            print(f"Error: Watch directory '{watch_dir}' does not exist.")
            sys.exit(1)
        
        # Create output dir if it doesn't exist
        output_dir.mkdir(parents=True, exist_ok=True)

        print(f"Monitoring {watch_dir}...")
        print(f"Outputting to {output_dir}")
        print("Press Ctrl+C to stop.")

        event_handler = NewFileHandler(output_dir)
        observer = Observer()
        observer.schedule(event_handler, str(watch_dir), recursive=False)
        observer.start()

        try:
            while True:
                time.sleep(1)
        except KeyboardInterrupt:
            observer.stop()
        observer.join()

if __name__ == "__main__":
    main()