🎥 CRF File Size Estimator

A simple web-based tool to help estimate the final file size of an H.264 or H.265 encode based on CRF value, preset, resolution, and optional audio configuration.

Perfect for users of HandBrake, FFmpeg, or anyone working with x264 or x265 encoders.

⚠️ Note: All estimation results are preliminary. This JavaScript tool is a conceptual prototype and has not yet been fully validated yet.

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🔧 Features of initial release 1.0

• Estimate target file size in MB/GB based on CRF efficiency

• Choose between x264 and x265 codecs

• Supports slow preset (currently fixed)

• Resolution presets: 1080p (Blu-ray) and 576p (DVD)

• Optional audio calculation:

  • Stereo (2.0) or Surround (5.1)
  • Runtime-based bitrate estimation

• Language switcher: English 🇬🇧 / Deutsch 🇩🇪

• Clean, responsive UI with a Reset button

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✨ New in Version 1.1

• 📂 Drag & Drop support for video files → Automatically fills in the source file size based on the dropped file
• 🔁 Improved Reset behavior → Drag & Drop area now resets to its initial state

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📊 New in Version 1.2

• CRF impact chart: Visualizes how file size changes across CRF values (16–30)

  • Uses the same estimation algorithm from the form
  • Helps users visually identify the best CRF for their target size
  • Updates live with your current configuration (codec, resolution, runtime, audio)

• 📈 Auto-displayed after each estimate

• 🧠 Especially helpful for learning how CRF compression behaves across encoders

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🆕 New in Version 1.3

• ➕ Optional source video bitrate input (kbit/s) → More accurate estimates possible when the exact video bitrate of the source is known.

• 🕒 Runtime moved out of the audio section → Needed for bitrate-based estimation as well.

• 🧮 Dual estimation method:

  • If a source video bitrate is provided → bitrate-based calculation is used.
  • If only source file size is given → file size-based calculation (as before).
  • If both are given → consistency check between both methods, with warnings if they differ by more than 10%.

• 🎵 Audio calculation unchanged (Stereo 320 kbit/s / 5.1 384 kbit/s), but now clearly marked as separate from the video bitrate.

• ⚠️ Validation & error messages improved to prevent invalid input combinations.

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🖼️ Screenshot

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🚀 Getting Started

Download the HTML file from the repository or simply open it in your browser using this link:

👉 Open CRF File Size Estimator