reencode.md

This file, reencode.sh, is a comprehensive Bash script designed to batch re-encode MKV video files for Plex, with a strong focus on:

• Preserving HDR video metadata and compatibility.
• Normalizing audio (AC3) using EBU R128 loudness standards, with optional two-pass normalization for better accuracy.
• Efficient parallel processing (up to 4 simultaneous jobs by default).
• Detailed progress reporting with a colorized progress bar.
• Robust error handling and clean resource management.

Key Features:

1. Batch Processing:
   You can provide individual MKV files or an entire directory. The script will find all .mkv files and process them.

2. HDR Handling:
   The script uses ffprobe to detect HDR and video color characteristics, passing the correct parameters to ffmpeg so HDR metadata is preserved in the output.

3. Audio Normalization:
   By default, it normalizes audio in a single pass. With the --two-pass flag, it runs a two-pass normalization for more precise loudness adjustment. The normalized track is encoded as AC3 at 640kbps.

4. Parallelism with Semaphore:
   Up to 4 files are processed at once (configurable via MAX_JOBS). The script uses a FIFO-based semaphore to manage concurrency safely.

5. Progress Reporting:
   It creates named pipes to collect progress from ffmpeg for each job and displays a live, colorized progress bar with spinner, showing completed, in-progress, queued, and finished files.

6. Graceful Shutdown & Cleanup:
   Handles interrupts (Ctrl+C) and ensures all child processes are terminated, pipes and temp files are cleaned, and no jobs are left hanging.

7. Dependency Checks:
   Requires ffmpeg, ffprobe, and jq (for JSON parsing).

8. Command-Line Usage:

   ./reencode.sh [--two-pass] file1.mkv file2.mkv ...
   ./reencode.sh [--two-pass] /path/to/directory/
   

Typical Workflow:

• You call the script with MKV files or a directory.
• It checks for dependencies.
• It expands the file list, calculates total duration, and initializes semaphores.
• For each file, it determines HDR and audio parameters, then calls ffmpeg to re-encode.
• Progress for each file is tracked and shown in real time.
• It cleans up all resources, even on interruption.

Who is it for?

• Users who want an easy way to prepare large libraries of MKV files for Plex, especially with HDR content and normalized audio.
• Anyone needing a robust, parallel, and automated video batch processor with safe shutdown and progress reporting.

How it works:

1. Main Script Launches multiple ffmpeg jobs in parallel (up to MAX_JOBS). For each input file, creates a named FIFO (progress.XYZ) for ffmpeg's progress output.

2. ffmpeg Jobs Each ffmpeg process encodes a file and outputs progress info (with -progress ) to its unique FIFO.

3. Monitor Processes For each ffmpeg job, a monitor process reads from the respective FIFO. It parses the progress and writes standardized lines (time, status, filename) to the global status FIFO.

4. Global FIFO (status) All monitor processes write to a single status FIFO (status.XXXXXX).

5. Progress Bar Printer The main script runs a background process that reads from the global status FIFO. It aggregates progress across all files and updates a single, global progress bar in the terminal.

Summary:

• Each ffmpeg job has its own progress FIFO and monitor.
• All monitors feed updates into a single global FIFO.
• The progress bar printer reads the global FIFO and updates the terminal.