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VideoTools/docs/Conversion_Settings.md

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docs/Conversion_Settings.md

Conversion Settings (v0.1.0)

This file documents the default FFmpeg parameters used in video-tools.sh and explains why they are chosen.

Output Format

All conversions produce:

Format: MP4  
Container: MPEG-4 Part 14  
Video Codec: H.264 (libx264)  
Audio Codec: AAC

Why MP4?

  • Universally supported across modern devices.
  • Balances quality, compression, and compatibility.
  • H.264 encoding provides excellent visual quality at modest bitrates.

Default Parameters

Parameter Value Purpose
-c:v libx264 H.264 video encoding Modern, efficient codec with wide hardware support
-crf 18 Constant Rate Factor Maintains near-lossless visual quality (lower = better)
-preset slow Encoding preset Improves compression efficiency at moderate CPU cost
-c:a aac Audio codec Standard high-quality stereo audio
-b:a 192k Audio bitrate Balances fidelity and file size
-movflags +faststart MP4 optimization Enables faster playback start in players or web streams
-fflags +genpts Timestamp repair Regenerates timestamps on older AVI/MPEG inputs

Quality vs. File Size

The CRF scale (used by FFmpeg) defines the balance between quality and compression:

CRF Description Typical Use
14–16 Near lossless Archival or professional mastering
18–20 High quality Everyday use, visually lossless
21–24 Medium quality Smaller file sizes with light compression
25+ Low quality Fast compression, noticeable loss

Default CRF: 18
Provides visually lossless results while reducing most AVI/MPG files to 40–60% smaller sizes.

Why Use Preset “slow”

The preset defines the trade-off between encoding speed and compression efficiency.
Range: ultrafast → veryslow.

  • slow offers excellent compression without excessive CPU time.
  • Typical speed: ~2–3× real-time on a midrange CPU.
  • Output files are usually 10–20% smaller than with medium preset at the same quality.

Audio Strategy

AAC at 192k is chosen for:

  • Broad device compatibility (phones, TVs, web players).
  • Transparent stereo sound for most content.
  • Efficient storage (~2 MB/min of stereo audio).

Future options may include:

  • -c:a copy for untouched audio streams.
  • -b:a 320k for high-fidelity preservation.

Color Space & Scaling

No scaling is applied by default — the video retains its original resolution and color profile.

Planned future command: upscale-video, supporting:

  • FFmpeg’s scale and zscale filters.
  • lanczos resampling for sharp, clean upscales.
  • Optional ML upscaling (Real-ESRGAN, waifu2x).

Future Additions

Planned Setting Description
upscale-mode Default scaling filter for upscaling tasks
hevc-mode Switch to H.265 (libx265) for smaller files
audio-pass Option to skip audio re-encoding
config.json User-editable file to override default values

End of File