Shrinking a 61‑Hour Stream Recording with FFMPEG on MacOS

#!/usr/bin/env bash
set -euo pipefail

# Default values
BITRATE="8M"
FPS="30"
NOTIFICATION=true
SOUND=true

# Function to display help message
show_help() {
    echo "Video Converter - Convert OBS MKV recordings to MP4"
    echo ""
    echo "Usage: $0 [options] <input-file>"
    echo ""
    echo "Options:"
    echo "  -h, --help           Show this help message"
    echo "  -b, --bitrate RATE   Set video bitrate (default: 8M)"
    echo "  -f, --fps RATE       Set frames per second (default: 30)"
    echo "  -o, --output FILE    Specify output filename (default: same as input with .mp4 extension)"
    echo "  --no-sound           Disable completion sound"
    echo "  --no-notification    Disable completion notification"
    echo ""
    echo "Example:"
    echo "  $0 --bitrate 10M --fps 60 recording.mkv"
    echo "  $0 -b 5M -o custom_name.mp4 recording.mkv"
    exit 0
}

# Parse command line arguments
INPUT=""
OUTPUT=""

while [[ $# -gt 0 ]]; do
    case "$1" in
        -h|--help)
            show_help
            ;;
        -b|--bitrate)
            if [[ $# -lt 2 ]]; then
                echo "Error: Option $1 requires an argument" >&2
                exit 1
            fi
            BITRATE="$2"
            shift 2
            ;;
        -f|--fps)
            if [[ $# -lt 2 ]]; then
                echo "Error: Option $1 requires an argument" >&2
                exit 1
            fi
            FPS="$2"
            shift 2
            ;;
        -o|--output)
            if [[ $# -lt 2 ]]; then
                echo "Error: Option $1 requires an argument" >&2
                exit 1
            fi
            OUTPUT="$2"
            shift 2
            ;;
        --no-sound)
            SOUND=false
            shift
            ;;
        --no-notification)
            NOTIFICATION=false
            shift
            ;;
        -*)
            echo "Error: Unknown option: $1" >&2
            echo "Use --help to see available options" >&2
            exit 1
            ;;
        *)
            if [[ -z "$INPUT" ]]; then
                INPUT="$1"
            else
                echo "Error: Multiple input files specified. Only one input file is supported." >&2
                echo "Use --help to see correct usage" >&2
                exit 1
            fi
            shift
            ;;
    esac
done

# Validate input file
if [[ -z "$INPUT" ]]; then
    echo "Error: No input file specified" >&2
    echo "Use --help to see correct usage" >&2
    exit 1
fi

if [[ ! -f "$INPUT" ]]; then
    echo "Error: Input file '$INPUT' does not exist" >&2
    exit 1
fi

# Validate bitrate format (should end with K or M)
if ! [[ "$BITRATE" =~ ^[0-9]+[KMkm]$ ]]; then
    echo "Warning: Bitrate '$BITRATE' doesn't follow the recommended format (e.g., 8M, 500K)" >&2
    read -p "Continue anyway? (y/N): " CONFIRM
    if [[ ! "$CONFIRM" =~ ^[Yy]$ ]]; then
        echo "Operation cancelled"
        exit 0
    fi
fi

# Validate FPS (should be a positive number)
if ! [[ "$FPS" =~ ^[0-9]+(\.[0-9]+)?$ ]] || [[ "$FPS" == "0" || "$FPS" == "0.0" ]]; then
    echo "Error: FPS must be a positive number" >&2
    exit 1
fi

# Set default output filename if not specified
if [[ -z "$OUTPUT" ]]; then
    OUTPUT="${INPUT%.*}.mp4"
fi

# Check if output file already exists
if [[ -e "$OUTPUT" ]]; then
    read -p "Output file '$OUTPUT' already exists. Overwrite? (y/N): " CONFIRM
    if [[ ! "$CONFIRM" =~ ^[Yy]$ ]]; then
        echo "Operation cancelled"
        exit 0
    fi
fi

echo "Converting '$INPUT' to '$OUTPUT'"
echo "Settings: Bitrate=$BITRATE, FPS=$FPS"
echo "Starting ffmpeg..."

# Run ffmpeg with progress display
ffmpeg -hide_banner -stats -i "$INPUT" \
  -map 0:v:0 -map 0:a:0 \
  -vf fps=${FPS} \
  -c:v hevc_videotoolbox -b:v "$BITRATE" -pix_fmt yuv420p \
  -c:a aac -b:a 128k \
  "$OUTPUT"

echo "Conversion complete: '$OUTPUT'"
# use the full path when reporting
echo "Newly encoded file created at $(realpath "$OUTPUT"); size: $(du -h "$OUTPUT" | cut -f1)"
echo "Original file: $(realpath "$INPUT"); size: $(du -h "$INPUT" | cut -f1)"

# Play sound notification if enabled
if [[ "$SOUND" == true ]]; then
    afplay /System/Library/Sounds/Submarine.aiff
fi

# Display system notification if enabled
if [[ "$NOTIFICATION" == true ]]; then
    osascript -e 'display notification "Encoding complete." with title "ffmpeg done"'
fi