minstrel/internal/library/replaygain.go

package library

import (
	"context"
	"math"

	"github.com/jackc/pgx/v5/pgtype"

	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
)

// ReplayGain delivery.
//
// Clients are handed loudness in the ReplayGain 2.0 form every player already
// understands: a gain in dB that brings the track (or album) to the RG2
// reference of -18 LUFS, and a linear peak. A client aiming at another target
// adds (target - ReplayGainReferenceLUFS) to the gain. The same numbers go to
// the native API, the sync feed and OpenSubsonic's replayGain, so every client
// levels a track identically.

// ReplayGainReferenceLUFS is the RG2 reference loudness gains are relative to.
const ReplayGainReferenceLUFS = -18.0

// ReplayGain is one track's gains. Each field is nil when there is nothing to
// say: not yet measured, silent, or (for the album pair) an album still
// waiting on a track. AlbumPeak travels only with AlbumGain.
type ReplayGain struct {
	TrackGain *float32 `json:"track_gain,omitempty"`
	TrackPeak *float32 `json:"track_peak,omitempty"`
	AlbumGain *float32 `json:"album_gain,omitempty"`
	AlbumPeak *float32 `json:"album_peak,omitempty"`
}

// Empty reports whether no gain is known at all.
func (g ReplayGain) Empty() bool {
	return g.TrackGain == nil && g.AlbumGain == nil
}

// GainDB converts an integrated loudness to its RG2 gain, to 0.01 dB.
func GainDB(lufs *float32) *float32 {
	if lufs == nil {
		return nil
	}
	v := float32(math.Round((ReplayGainReferenceLUFS-float64(*lufs))*100) / 100)
	return &v
}

// LinearPeak converts a true peak in dBTP to the linear amplitude ReplayGain
// peaks are written in (1.0 is full scale), to 4 decimals.
func LinearPeak(dbtp *float32) *float32 {
	if dbtp == nil {
		return nil
	}
	v := float32(math.Round(math.Pow(10, float64(*dbtp)/20)*10000) / 10000)
	return &v
}

// ReplayGainForTracks returns the gains for each of ids that has any. Tracks
// with none are absent from the map, so a lookup of a missing key yields the
// zero ReplayGain: no adjustment.
func ReplayGainForTracks(ctx context.Context, q *dbq.Queries, ids []pgtype.UUID) (map[pgtype.UUID]ReplayGain, error) {
	out := make(map[pgtype.UUID]ReplayGain, len(ids))
	if len(ids) == 0 {
		return out, nil
	}
	rows, err := q.GetReplayGainByTrackIDs(ctx, ids)
	if err != nil {
		return nil, err
	}
	for _, r := range rows {
		g := ReplayGain{TrackGain: GainDB(r.TrackLufs)}
		if g.TrackGain != nil {
			g.TrackPeak = LinearPeak(r.TrackPeakDbtp)
		}
		if g.AlbumGain = GainDB(r.AlbumLufs); g.AlbumGain != nil {
			g.AlbumPeak = LinearPeak(r.AlbumPeakDbtp)
		}
		if !g.Empty() {
			out[r.ID] = g
		}
	}
	return out, nil
}

// ReplayGainForAlbums returns the album pair for each of albumIDs that has an
// album loudness. The track fields are left nil.
func ReplayGainForAlbums(ctx context.Context, q *dbq.Queries, albumIDs []pgtype.UUID) (map[pgtype.UUID]ReplayGain, error) {
	out := make(map[pgtype.UUID]ReplayGain, len(albumIDs))
	if len(albumIDs) == 0 {
		return out, nil
	}
	rows, err := q.GetAlbumLoudnessByIDs(ctx, albumIDs)
	if err != nil {
		return nil, err
	}
	for _, r := range rows {
		if g := GainDB(r.IntegratedLufs); g != nil {
			out[r.AlbumID] = ReplayGain{AlbumGain: g, AlbumPeak: LinearPeak(r.TruePeakDbtp)}
		}
	}
	return out, nil
}