refactor: move shared packages up a level

transcode/transcode.go

@@ -0,0 +1,129 @@
+// author: spijet (https://github.com/spijet/)
+// author: sentriz (https://github.com/sentriz/)
+
+//nolint:gochecknoglobals
+package transcode
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"os/exec"
+	"time"
+
+	"github.com/google/shlex"
+)
+
+type Transcoder interface {
+	Transcode(ctx context.Context, profile Profile, in string) (io.ReadCloser, error)
+}
+
+var UserProfiles = map[string]Profile{
+	"mp3":      MP3,
+	"mp3_rg":   MP3RG,
+	"opus_car": OpusCar,
+	"opus":     Opus,
+	"opus_rg":  OpusRG,
+}
+
+// Store as simple strings, since we may let the user provide their own profiles soon
+var (
+	MP3   = NewProfile("audio/mpeg", 128, `ffmpeg -v 0 -i <file> -ss <seek> -map 0:a:0 -vn -b:a <bitrate> -c:a libmp3lame -af "volume=replaygain=track:replaygain_preamp=6dB:replaygain_noclip=0, alimiter=level=disabled, asidedata=mode=delete:type=REPLAYGAIN" -metadata replaygain_album_gain= -metadata replaygain_album_peak= -metadata replaygain_track_gain= -metadata replaygain_track_peak= -metadata r128_album_gain= -metadata r128_track_gain= -f mp3 -`)
+	MP3RG = NewProfile("audio/mpeg", 128, `ffmpeg -v 0 -i <file> -ss <seek> -map 0:a:0 -vn -b:a <bitrate> -c:a libmp3lame -af "volume=replaygain=track:replaygain_preamp=6dB:replaygain_noclip=0, alimiter=level=disabled, asidedata=mode=delete:type=REPLAYGAIN" -metadata replaygain_album_gain= -metadata replaygain_album_peak= -metadata replaygain_track_gain= -metadata replaygain_track_peak= -metadata r128_album_gain= -metadata r128_track_gain= -f mp3 -`)
+
+	// this sets a baseline gain which results in the final track being +3~5dB louder than
+	// Foobar2000's default ReplayGain target volume.
+	// this makes it easier to listen to music in a car, where all other
+	// sources are usually ten thousand times louder than RG-adjusted music.
+	//
+	// opus always forces output to 48kHz sampling rate, but we can still use upsampling
+	// to increase RG and alimiter's peak limiting precision, which is desirable in some
+	// cases. ffmpeg's `soxr` resampler is quite fast on x86-64: it takes around 5 seconds
+	// on my Ryzen 3600 to transcode an 8-minute FLAC with 2x upsample and RG applied.
+	//
+	// -- @spijet
+	OpusCar = NewProfile("audio/ogg", 96, `ffmpeg -v 0 -i <file> -ss <seek> -map 0:a:0 -vn -b:a <bitrate> -c:a libopus -vbr on -af "aresample=96000:resampler=soxr, volume=replaygain=track:replaygain_preamp=15dB:replaygain_noclip=0, alimiter=level=disabled, asidedata=mode=delete:type=REPLAYGAIN" -f opus -`)
+	Opus    = NewProfile("audio/ogg", 96, `ffmpeg -v 0 -i <file> -ss <seek> -map 0:a:0 -vn -b:a <bitrate> -c:a libopus -vbr on -af "volume=replaygain=track:replaygain_preamp=6dB:replaygain_noclip=0, alimiter=level=disabled, asidedata=mode=delete:type=REPLAYGAIN" -metadata replaygain_album_gain= -metadata replaygain_album_peak= -metadata replaygain_track_gain= -metadata replaygain_track_peak= -metadata r128_album_gain= -metadata r128_track_gain= -f opus -`)
+	OpusRG  = NewProfile("audio/ogg", 96, `ffmpeg -v 0 -i <file> -ss <seek> -map 0:a:0 -vn -b:a <bitrate> -c:a libopus -vbr on -af "volume=replaygain=track:replaygain_preamp=6dB:replaygain_noclip=0, alimiter=level=disabled, asidedata=mode=delete:type=REPLAYGAIN" -metadata replaygain_album_gain= -metadata replaygain_album_peak= -metadata replaygain_track_gain= -metadata replaygain_track_peak= -metadata r128_album_gain= -metadata r128_track_gain= -f opus -`)
+
+	PCM16le = NewProfile("audio/wav", 0, `ffmpeg -v 0 -i <file> -ss <seek> -c:a pcm_s16le -ac 2 -f s16le -`)
+)
+
+type BitRate int // kb/s
+
+type Profile struct {
+	bitrate BitRate // the default bitrate, but the user can request a different one
+	seek    time.Duration
+	mime    string
+	exec    string
+}
+
+func (p *Profile) BitRate() BitRate    { return p.bitrate }
+func (p *Profile) Seek() time.Duration { return p.seek }
+func (p *Profile) MIME() string        { return p.mime }
+
+func NewProfile(mime string, bitrate BitRate, exec string) Profile {
+	return Profile{mime: mime, bitrate: bitrate, exec: exec}
+}
+
+func WithBitrate(p Profile, bitRate BitRate) Profile {
+	p.bitrate = bitRate
+	return p
+}
+func WithSeek(p Profile, seek time.Duration) Profile {
+	p.seek = seek
+	return p
+}
+
+var ErrNoProfileParts = fmt.Errorf("not enough profile parts")
+
+func parseProfile(profile Profile, in string) (string, []string, error) {
+	parts, err := shlex.Split(profile.exec)
+	if err != nil {
+		return "", nil, fmt.Errorf("split command: %w", err)
+	}
+	if len(parts) == 0 {
+		return "", nil, ErrNoProfileParts
+	}
+	name, err := exec.LookPath(parts[0])
+	if err != nil {
+		return "", nil, fmt.Errorf("find name: %w", err)
+	}
+
+	var args []string
+	for _, p := range parts[1:] {
+		switch p {
+		case "<file>":
+			args = append(args, in)
+		case "<seek>":
+			args = append(args, fmt.Sprintf("%dus", profile.Seek().Microseconds()))
+		case "<bitrate>":
+			args = append(args, fmt.Sprintf("%dk", profile.BitRate()))
+		default:
+			args = append(args, p)
+		}
+	}
+
+	return name, args, nil
+}
+
+// GuessExpectedSize guesses how big the transcoded file will be in bytes.
+// Handy if we want to send a Content-Length header to the client before
+// the transcode has finished. This way, clients like DSub can render their
+// scrub bar and duration as the track is streaming.
+//
+// The estimate should overshoot a bit (2s in this case) otherwise some HTTP
+// clients will shit their trousers given some unexpected bytes.
+func GuessExpectedSize(profile Profile, length time.Duration) int {
+	if length == 0 {
+		return 0
+	}
+
+	bytesPerSec := int(profile.BitRate() * 1000 / 8)
+
+	var guess int
+	guess += bytesPerSec * int(length.Seconds()-profile.seek.Seconds())
+	guess += bytesPerSec * 2 // 2s pading
+	guess += 10000           // 10kb byte padding
+	return guess
+}