/
transcode.go
129 lines (109 loc) · 5.53 KB
/
transcode.go
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// 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
}