Add per-disk profiles with video transcoding support

Each disk stores .jukebox/profile.json with copy parameters (dest
folder, overwrite mode, file select, reserve space, auto-copy) and
optional transcoding limits for the target player (codec, resolution,
bitrate, FPS, audio channels, output format).

On copy, video files are probed with ffprobe; if they exceed the
profile limits they are transcoded via ffmpeg (-threads 0 for full
CPU usage), otherwise copied as-is. Scale filter never upscales.

New: internal/disk/profile.go, internal/transcoder/{detect,transcoder}.go
API: GET/PUT /api/disks/profile?mount_path=
UI: disk profile panel in dashboard for known disks
Dockerfile: adds ffmpeg to the runtime image

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/transcoder/transcoder.go

@@ -0,0 +1,167 @@
+package transcoder
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	"jukebox_maker/internal/disk"
+)
+
+type Options struct {
+	Input      string
+	Output     string
+	Profile    *disk.TranscodeProfile
+	SourceInfo VideoInfo
+}
+
+// Transcode запускает ffmpeg. progress вызывается с 0..1 по мере работы.
+func Transcode(ctx context.Context, opts Options, progress func(float64)) error {
+	if err := os.MkdirAll(filepath.Dir(opts.Output), 0o755); err != nil {
+		return err
+	}
+
+	args := buildArgs(opts)
+	cmd := exec.CommandContext(ctx, "ffmpeg", args...)
+
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return err
+	}
+	var stderr bytes.Buffer
+	cmd.Stderr = &stderr
+
+	if err := cmd.Start(); err != nil {
+		return fmt.Errorf("ffmpeg start: %w", err)
+	}
+
+	// Парсим прогресс из stdout (-progress pipe:1)
+	if opts.SourceInfo.DurationSec > 0 && progress != nil {
+		scanner := bufio.NewScanner(stdout)
+		for scanner.Scan() {
+			line := scanner.Text()
+			if strings.HasPrefix(line, "out_time_us=") {
+				val := strings.TrimPrefix(line, "out_time_us=")
+				if us, err := strconv.ParseInt(val, 10, 64); err == nil && us > 0 {
+					sec := float64(us) / 1e6
+					pct := sec / opts.SourceInfo.DurationSec
+					if pct > 1 {
+						pct = 1
+					}
+					progress(pct)
+				}
+			}
+		}
+	}
+
+	if err := cmd.Wait(); err != nil {
+		msg := strings.TrimSpace(stderr.String())
+		if msg != "" {
+			return fmt.Errorf("ffmpeg: %w: %s", err, msg)
+		}
+		return fmt.Errorf("ffmpeg: %w", err)
+	}
+	return nil
+}
+
+func buildArgs(opts Options) []string {
+	p := opts.Profile
+	src := opts.SourceInfo
+
+	args := []string{
+		"-i", opts.Input,
+		"-threads", "0",
+		"-progress", "pipe:1",
+		"-v", "error",
+	}
+
+	// Видеокодек
+	args = append(args, "-c:v", ffmpegVideoCodec(p.VideoCodec))
+
+	// Битрейт — только если источник выше лимита
+	if p.MaxVideoBitrate != "" {
+		if targetBR := parseBitrate(p.MaxVideoBitrate); targetBR > 0 &&
+			(src.VideoBitrate == 0 || src.VideoBitrate > targetBR) {
+			args = append(args, "-b:v", p.MaxVideoBitrate)
+		}
+	}
+
+	// Масштаб + FPS — строим vf
+	var filters []string
+	if maxH := maxHeight(p.MaxResolution); maxH > 0 {
+		filters = append(filters, fmt.Sprintf("scale=-2:min(%d\\,ih)", maxH))
+	}
+	if p.MaxFPS > 0 && src.FPS > float64(p.MaxFPS)+0.01 {
+		filters = append(filters, fmt.Sprintf("fps=%d", p.MaxFPS))
+	}
+	if len(filters) > 0 {
+		args = append(args, "-vf", strings.Join(filters, ","))
+	}
+
+	// Аудиокодек
+	if p.AudioCodec != "" {
+		args = append(args, "-c:a", ffmpegAudioCodec(p.AudioCodec))
+	} else {
+		args = append(args, "-c:a", "copy")
+	}
+
+	// Аудио-битрейт
+	if p.MaxAudioBitrate != "" {
+		args = append(args, "-b:a", p.MaxAudioBitrate)
+	}
+
+	// Каналы — только даунмикс
+	if p.MaxAudioChannels > 0 && src.AudioChannels > p.MaxAudioChannels {
+		args = append(args, "-ac", strconv.Itoa(p.MaxAudioChannels))
+	}
+
+	// Для mp4 — оптимизация для стриминга
+	if p.OutputFormat == "mp4" {
+		args = append(args, "-movflags", "+faststart")
+	}
+
+	args = append(args, "-y", opts.Output)
+	return args
+}
+
+func ffmpegVideoCodec(codec string) string {
+	switch codec {
+	case "h264":
+		return "libx264"
+	case "h265":
+		return "libx265"
+	case "mpeg4":
+		return "mpeg4"
+	default:
+		return "libx264"
+	}
+}
+
+func ffmpegAudioCodec(codec string) string {
+	switch codec {
+	case "aac":
+		return "aac"
+	case "mp3":
+		return "libmp3lame"
+	default:
+		return "aac"
+	}
+}
+
+// OutputExt возвращает расширение файла для заданного формата контейнера.
+func OutputExt(format string) string {
+	switch format {
+	case "mkv":
+		return ".mkv"
+	case "avi":
+		return ".avi"
+	default:
+		return ".mp4"
+	}
+}