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Encoding Configuration Parameters

This document details the configuration parameters used across the AomEnc and SVT-AV1 encoding scripts.

Audio Demuxing & Downmixing

The audio processing extracts streams using ffmpeg and automatically downmixes surround layouts to stereo if requested.

Downmixing Parameters

  • 5.1 Channel Layouts (6 channels)

    -af "pan=stereo|c0=c2+0.30*c0+0.30*c4|c1=c2+0.30*c1+0.30*c5"

  • 7.1 Channel Layouts (8 channels)

    -af "pan=stereo|c0=c2+0.30*c0+0.30*c4+0.30*c6|c1=c2+0.30*c1+0.30*c5+0.30*c7"

Non-Downmixed Encoding Bitrates (Opus)

When preserving the original channel layout (no downmixing) or if the source is already stereo/mono, audio is encoded with the following bitrates based on channel count:

  • Mono (1 channel): 64k
  • Stereo (2 channels): 128k
  • 5.1 Surround (6 channels): 256k
  • 7.1 Surround (8 channels): 384k
  • Other/Uncommon Layouts: 192k (fallback default)

VFR to CFR Conversion

To handle Variable Frame Rate (VFR) sources reliably on UTVideo intermediate generation, HandBrakeCLI is used to convert them to Constant Frame Rate (CFR) before processing.

The exact HandBrakeCLI arguments used:

HandBrakeCLI \
  --input <source_file> \
  --output <intermediate_cfr_file> \
  --cfr \
  --rate <target_cfr_fps> \
  --encoder x264_10bit \
  --quality 0 \
  --encoder-preset superfast \
  --encoder-tune fastdecode \
  --audio none \
  --subtitle none \
  --crop-mode none

Encoder-Specific Parameters

AomEnc (aom-psy101)

Special Version Repository: https://gitlab.com/damian101/aom-psy101

Parameters parsed to the aom encoder:

Parameter Value Description
--bit-depth 10 Force 10-bit encoding for better color precision and less banding
--cpu-used 2 Speed preset. Lower is slower/better quality. 4 is default, 2 is slow/high quality
--end-usage q Constant Quality mode
--cq-level 25 The target quality level (0-63). Lower is better quality/larger file
--min-q 12 Minimum allowable quantizer to prevent bitrate spikes on flat frames
--threads 2 Threads per av1an worker
--tune-content psy Specialized tuning for psychovisual quality (needs aom-psy101)
--tune ssim Protects structural edges universally
--sharpness 1 Edge protection that won't cause halos in live-action
--arnr-maxframes 5 Middle-ground temporal filtering (default is 7)
--arnr-strength 3 Middle-ground filtering strength (default is 5)
--quant-b-adapt 1 Universal B-frame efficiency
--frame-parallel 1 Enable frame parallel decoding
--tile-columns 1 Use 2 tile columns (2^1) for faster decoding
--gf-max-pyr-height 4 Golden Frame pyramid height (max is 5)
--deltaq-mode 2 Enable perceptual quantizer (AQ mode based on variance)
--enable-keyframe-filtering 0 We disable internal KF filtering as av1an handles chunking
--disable-kf (flag) Disable internal keyframes (av1an inserts them at scene cuts)
--enable-fwd-kf 0 Disable forward keyframes
--kf-max-dist 9999 Set max keyframe distance arbitrarily high
--sb-size dynamic Allow the encoder to choose 64x64 or 128x128 superblocks dynamically
--enable-chroma-deltaq 1 Enable chroma quantization adjustment
--enable-qm 1 Enable quantization matrices for better high-frequency detail retention
--color-primaries bt709 Standard SDR color space
--transfer-characteristics bt709 Standard SDR transfer characteristics
--matrix-coefficients bt709 Standard SDR matrix coefficients

(Note: --cq-level dynamically defaults to 25 but can be overwritten when executing the script via the --crf argument).

SVT-AV1 (SVT-AV1-Essential)

Special Version Repository: https://github.com/nekotrix/SVT-AV1-Essential/

Parameters initialized for the svt-av1 encoder:

Parameter Value Description
--preset 2 Speed preset. Lower is slower and yields better compression efficiency.
--crf 30 Constant Rate Factor (CRF). Lower is better quality.
--film-grain 6 Film grain synthesis level. Adds artificial grain to preserve detail and prevent banding.
--color-primaries 1 BT.709 color primaries (Standard SDR).
--transfer-characteristics 1 BT.709 transfer characteristics (Standard SDR).
--matrix-coefficients 1 BT.709 matrix coefficients (Standard SDR).
--scd 0 Scene change detection OFF (av1an handles scene cuts).
--keyint 0 Keyframe interval OFF (av1an inserts keyframes).
--lp 2 Logical Processors to use per av1an worker.
--auto-tiling 1 Automatically determine the number of tiles based on resolution.
--tune 0 0 = VQ, 1 = PSNR, 2 = SSIM (SVT-AV1-Essential default recommended).
--progress 2 Detailed progress output.

(Note: Parameters such as --preset, --crf, and --film-grain can be overridden when executing the script).

av1an Initiation Commands

AomEnc

Arguments used to start av1an using the AomEnc encoder:

av1an -i <vpy_script> -o <encoded_mkv> -n \
  -e aom \
  --photon-noise <grain> \
  --resume \
  --sc-pix-format yuv420p \
  -c mkvmerge \
  --set-thread-affinity 2 \
  --pix-format yuv420p10le \
  --force \
  --no-defaults \
  -w <calculated_workers> \
  --passes 2 \
  -v "<aom_encoder_parameters_above>"

SVT-AV1

Arguments used to start av1an using the SVT-AV1 encoder:

av1an -i <vpy_script> -o <encoded_mkv> -n \
  -e svt-av1 \
  --resume \
  --sc-pix-format yuv420p \
  -c mkvmerge \
  --set-thread-affinity 2 \
  --pix-format yuv420p10le \
  --force \
  --no-defaults \
  -w <calculated_workers> \
  -v "<svt_av1_encoder_parameters_above>"