🎬 20MB Video Compressor (Termux)

A smart Bash script that compresses videos to a user-defined target size using ffmpeg, designed for Termux and lightweight environments.

💬 Discord Note: Discord currently allows 20MB uploads for free users. The script defaults to 20MB for safety (targeting ~95% to account for container overhead) but lets you choose another target size interactively at runtime.

Perfect for:

• Discord uploads (20MB free limit — 20MB default)
• Quick file sharing
• Mobile encoding via Termux
• Low-resource Linux systems

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📦 Features

• 🎯 User-selectable target output size (default 20MB)
• 🔁 2-pass encoding for accurate size targeting
• 🛡️ 95% safety margin calculation to account for container metadata overhead
• 📊 Real-time progress bar (built with pure Bash to prevent subshell errors)
• 🛠️ Robust N/A duration handling and metadata fallbacks
• 🧠 Automatic bitrate calculation with minimum bitrate floors
• 🔊 Smart audio/video bitrate allocation (with mute support)
• 📐 Auto resolution detection
• 📉 Auto downscale to 720p if width > 1280px
• ⚡ Uses all available CPU cores (nproc with fallback)
• 📱 Fully optimized for Termux & minimal systems
• 🧹 Automatic temporary file and isolated pass-log cleanup

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🛠 Requirements

You need:

• bash
• ffmpeg
• ffprobe
• coreutils (for wc, stat, or nproc, usually preinstalled)

Install in Termux:

pkg update
pkg install ffmpeg coreutils

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🚀 Usage

chmod +x compress20mb.sh
./compress20mb.sh input.mp4 output.mp4

When running, you will be prompted:

Enter target size in MB (default 20 MB):

• Press Enter to keep 20MB
• Type 8, 10, or any other number to change target size

Example:

./compress20mb.sh video.mp4 compressed.mp4

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⚙️ How It Works

1. Prompts for target size (default 20MB) and optional audio removal.
2. Reads video duration using ffprobe (falling back to video stream duration if container metadata is missing/N/A).
3. Calculates total available bits with a 5% safety margin for container overhead.
4. Reserves 64 kbps for audio (or 0 kbps if muted).
5. Assigns remaining bitrate to video (ensuring a minimum floor of 64 kbps).
6. Downscales to 720p if width > 1280px.
7. Performs isolated 2-pass encoding:

• Pass 1: analysis pass outputting to isolated process log files.
• Pass 2: final encode with real-time Termux-compatible progress tracking.

8. If file exceeds target (verified via exact byte checks):

• Reduces video bitrate by 5%
• Re-encodes automatically

9. Cleans up temporary files and pass logs.

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🧮 Bitrate Formula

Target size (MB) × 8192 × 0.95 = total available kilobits
Total kilobits ÷ duration (seconds) = total bitrate (kbps)
Video bitrate = total bitrate − audio bitrate

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📊 Example Output

══════════════════════════════════════
 Duration: 214s
 Target: 20MB (Targeting ~95% safety ceiling)
 Video Bitrate: 727k
 Audio Bitrate: 64k
 Threads: 8
 Scaling: 720p
 Codec: libx264 (2-pass)
══════════════════════════════════════
Progress: [##########################          ] 54% (115s/214s)
Done: output.mp4 (18.84MB)

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⚠️ Notes

• Output size will never exceed target
• Very long videos will have lower quality (bitrate constrained)
• Very short videos may look very high quality
• Uses all logical CPU cores detected via nproc
• Designed for reliability, Termux compatibility, and failure protection over raw speed

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🔧 Customization

You can change the default prompt value or modify audio/preset options:

# Default prompt value
DEFAULT_TARGET_MB=20

# Change audio bitrate (kbps)
AUDIO_BITRATE=64

# Change x264 preset
-preset fast

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🆚 Why 2-Pass?

2-pass encoding:

• Improves bitrate distribution across variable-complexity scenes
• Ensures accurate file size target matching
• Produces better quality at low bitrates
• Guarantees ≤ TARGET_MB output

This version prioritizes accuracy, reliability, and full Termux compatibility while remaining lightweight.

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📄 License

MIT License — free to use and modify.