docs: document encoding setting versions

docs/encoding_versions.md

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+# Encoding Settings Version 1.0
+
+This document describes the encoding settings used by videnc version 1.0 for all video encodings.
+
+## Universal Settings
+
+These settings are applied to all videos regardless of source material:
+
+- **Video Codec**: libsvtav1 (AV1)
+- **Pixel Format**: yuv420p10le
+- **Preset**: 4 (universal setting)
+- **enable-overlays**: 1 (enabled for all encodings)
+- **enable-qm**: 1 (enabled for all encodings)
+- **qm-min**: 0
+- **qm-max**: 15
+- **scd**: 1 (scene change detection enabled)
+- **film-grain-denoise**: 1 (enabled for all encodings)
+- **tune**: 0 (default tuning)
+
+## Variable Settings
+
+These settings vary based on video characteristics:
+
+### Resolution-Based Settings
+- **CRF**: 30 for videos < 1 MPixel, 28 for videos >= 1 MPixel
+- **film-grain**: 10 for videos < 1 MPixel, 5 for videos >= 1 MPixel
+
+## Source Material Dependent Settings
+
+These settings are conditionally applied based on the characteristics of the source video:
+
+- **Deinterlacing**: Applied when `isInterlaced` is detected
+  - Filter: `bwdif=mode=0`
+  
+- **Anamorphic Correction**: Applied when `isAnamorphic` is detected
+  - Filter chain: `scale=iw*sar:ih:lanczos,setsar=1,scale=-2:ih:lanczos`
+  
+- **Keyframe Interval**: Dynamically calculated based on video FPS
+  - Value: `Math.round(videoInfo.fps * 5)`
+
+## Audio Settings
+
+- **Audio Codec**: libopus for all audio streams
+- **Channel Layout**: Preserved from source (with special handling for sideloaded audio)
+- **Language Metadata**: Preserved for each stream
+- **Disposition**: English audio tracks set as default
+
+## Subtitle Settings
+
+- **Subtitle Handling**: Copy (no re-encoding)
+- **Language Metadata**: Preserved for each stream
+- **Disposition**: Finnish subtitle tracks set as default
+
+## Metadata Handling
+
+- **Metadata Stripping**: Original metadata is stripped (`-map_metadata -1`)
+- **Custom Metadata**: Added from OMDB API or user input
+- **Encoding Version**: Added as `ENCODING_VERSION=1.0`