internal/thumbs is internal/media, with Inspect: what a file holds, from ffprobe

The package was named for its first job; it now also decides what a file is for the
Files tab (image, video, audio) and reads its streams, which the viewer will need. Inspect
is the richer probe — codec, profile, pixel format, size, frame rate, HDR transfer, the
audio beside it, container and duration — run as root through sudo when asked.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/media/inspect.go

@@ -0,0 +1,142 @@
+package media
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"os/exec"
+	"strconv"
+	"strings"
+
+	"hamlab/internal/priv"
+)
+
+// Stream is one stream of a media file, as ffprobe reports it.
+type Stream struct {
+	Index         int     `json:"index"`
+	Type          string  `json:"type"` // video | audio
+	Codec         string  `json:"codec"`
+	Profile       string  `json:"profile,omitempty"`
+	PixFmt        string  `json:"pix_fmt,omitempty"`
+	Width         int     `json:"width,omitempty"`
+	Height        int     `json:"height,omitempty"`
+	FPS           float64 `json:"fps,omitempty"`
+	ColorTransfer string  `json:"color_transfer,omitempty"` // smpte2084 / arib-std-b67 mean HDR
+	Channels      int     `json:"channels,omitempty"`
+	AttachedPic   bool    `json:"attached_pic,omitempty"`
+}
+
+// Info is what a file holds: the picture to take, the sound to go with it, and the whole.
+type Info struct {
+	Container string  `json:"container"` // "matroska,webm", "mov,mp4,m4a,3gp,3g2,mj2"
+	Duration  float64 `json:"duration"`
+	BitRate   int64   `json:"bit_rate,omitempty"` // bits per second, whole file
+	Size      int64   `json:"size,omitempty"`
+	Video     *Stream `json:"video,omitempty"` // the first real picture stream; cover art is not it
+	Audio     *Stream `json:"audio,omitempty"` // the first sound stream
+}
+
+// HDR reports a picture that needs tone mapping to look right on an SDR screen.
+func (i Info) HDR() bool {
+	return i.Video != nil && (i.Video.ColorTransfer == "smpte2084" || i.Video.ColorTransfer == "arib-std-b67")
+}
+
+type probeJSON struct {
+	Streams []struct {
+		Index         int    `json:"index"`
+		CodecType     string `json:"codec_type"`
+		CodecName     string `json:"codec_name"`
+		Profile       string `json:"profile"`
+		PixFmt        string `json:"pix_fmt"`
+		Width         int    `json:"width"`
+		Height        int    `json:"height"`
+		RFrameRate    string `json:"r_frame_rate"`
+		AvgFrameRate  string `json:"avg_frame_rate"`
+		ColorTransfer string `json:"color_transfer"`
+		Channels      int    `json:"channels"`
+		Disposition   struct {
+			AttachedPic int `json:"attached_pic"`
+		} `json:"disposition"`
+	} `json:"streams"`
+	Format struct {
+		FormatName string `json:"format_name"`
+		Duration   string `json:"duration"`
+		BitRate    string `json:"bit_rate"`
+		Size       string `json:"size"`
+	} `json:"format"`
+}
+
+// Inspect asks ffprobe what a file is. As root through sudo when asked, for a file only
+// root may read. An error about the file itself is a DecodeError.
+func Inspect(ctx context.Context, c Caps, path string, root bool) (Info, error) {
+	if c.FFprobe == "" {
+		return Info{}, errors.New("ffprobe is not installed")
+	}
+	argv := []string{c.FFprobe, "-v", "error", "-show_entries",
+		"stream=index,codec_type,codec_name,profile,pix_fmt,width,height,r_frame_rate,avg_frame_rate,color_transfer,channels,disposition:format=format_name,duration,bit_rate,size",
+		"-of", "json", path}
+	if root {
+		argv = priv.Wrap(argv...)
+	}
+	cmd := exec.CommandContext(ctx, argv[0], argv[1:]...)
+	var errb bytes.Buffer
+	cmd.Stderr = &errb
+	out, err := cmd.Output()
+	if err != nil {
+		if ctx.Err() != nil {
+			return Info{}, ctx.Err()
+		}
+		msg := lastLine(errb.String())
+		if msg == "" {
+			msg = "ffprobe: " + err.Error()
+		}
+		return Info{}, &DecodeError{Msg: msg}
+	}
+	var pj probeJSON
+	if err := json.Unmarshal(out, &pj); err != nil {
+		return Info{}, &DecodeError{Msg: "ffprobe: unreadable answer"}
+	}
+	in := Info{Container: pj.Format.FormatName}
+	in.Duration, _ = strconv.ParseFloat(pj.Format.Duration, 64)
+	in.BitRate, _ = strconv.ParseInt(pj.Format.BitRate, 10, 64)
+	in.Size, _ = strconv.ParseInt(pj.Format.Size, 10, 64)
+	var art *Stream
+	for _, s := range pj.Streams {
+		st := &Stream{Index: s.Index, Type: s.CodecType, Codec: s.CodecName, Profile: s.Profile, PixFmt: s.PixFmt, Width: s.Width, Height: s.Height,
+			ColorTransfer: s.ColorTransfer, Channels: s.Channels, AttachedPic: s.Disposition.AttachedPic != 0}
+		st.FPS = fps(s.AvgFrameRate)
+		if st.FPS == 0 {
+			st.FPS = fps(s.RFrameRate)
+		}
+		switch {
+		case s.CodecType == "video" && st.AttachedPic:
+			if art == nil {
+				art = st
+			}
+		case s.CodecType == "video" && in.Video == nil:
+			in.Video = st
+		case s.CodecType == "audio" && in.Audio == nil:
+			in.Audio = st
+		}
+	}
+	if in.Video == nil {
+		in.Video = art // cover art is the only picture there is
+	}
+	return in, nil
+}
+
+// fps parses ffprobe's "60000/1001".
+func fps(r string) float64 {
+	n, d, ok := strings.Cut(r, "/")
+	if !ok {
+		v, _ := strconv.ParseFloat(r, 64)
+		return v
+	}
+	nf, _ := strconv.ParseFloat(n, 64)
+	df, _ := strconv.ParseFloat(d, 64)
+	if df == 0 {
+		return 0
+	}
+	return nf / df
+}