Scaling
flags needs channel config 0.1.2, which is not released yet. ErsatzTV Next v0.2.0 always uses fast_bilinear.
ErsatzTV Next scales each item to the channel's resolution. When the scale runs in software (ffmpeg's scale filter), normalization.video.filters.scale.flags sets the scaling algorithm:
{
"version": "https://ersatztv.org/channel/version/0.1.2",
"normalization": {
"video": {
"filters": {
"scale": {
"flags": "lanczos"
}
}
}
}
}
If flags is not set, ErsatzTV Next uses bicubic.
The setting applies everywhere the software scaler runs: the main picture, watermarks and other graphics, and image-based subtitles. It also applies to hardware-accelerated channels when a step falls back to software scaling. Hardware scalers (e.g. scale_cuda, scale_vaapi, vpp_qsv) are not affected.
Values
flags is passed to ffmpeg as-is, so any swscale flags work, including combinations joined with +. Suggested values:
flags | Use |
|---|---|
bicubic | Default. Good quality at low cost. |
lanczos | Slightly sharper than bicubic, at nearly twice the scaling cost. |
bicubic+accurate_rnd+full_chroma_int | bicubic with more accurate rounding and chroma. |
fast_bilinear | Lowest CPU use. Visibly aliased when downscaling, e.g. stair-stepped text and shimmering detail. |
flags may only contain lowercase letters, digits, _, ., + and -. ErsatzTV Next rejects any other value when it loads the channel config.
Cost
Scaling is a small part of a software transcode. Compared to fast_bilinear, a full software pipeline (decode, scale, libx264 encode) used under 1% more CPU with bicubic and about 3% more with lanczos, for both 1080p → 720p and 4K HDR → 1080p.
The difference is largest when scaling is the only software step, e.g. software decode and scale with a hardware encoder. There, bicubic adds roughly 1–8 ms of CPU per frame over fast_bilinear, depending on resolution (highest for 4K sources).
ErsatzTV (Legacy)
ErsatzTV channels that use the next engine have no setting for this in the UI. To change it, set flags in a channel config overlay in ErsatzTV's config folder / next / channel-config-overlays (default.json for all channels, or {number}.json for one channel), using the example above.
The legacy engine always uses fast_bilinear.