更新缩略图

backend/internal/service/video_frames.go

@@ -0,0 +1,76 @@
+package service
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+)
+
+// lastFrameSuffix marks a video's FULL-RESOLUTION last-frame still
+// ("u/x.mp4" → "u/x.mp4.last.jpg"). The 画图台 uses it as the 首帧 reference
+// when continuing a video (首尾帧 models); the first-frame THUMBNAIL reuses
+// thumbSuffix so list views load videos and images the same way.
+const lastFrameSuffix = ".last.jpg"
+
+// LastFrameKey returns the last-frame object key for a video key, and
+// IsLastFrameKey reports whether name refers to such a derived object.
+func LastFrameKey(rel string) string      { return rel + lastFrameSuffix }
+func IsLastFrameKey(name string) bool     { return strings.HasSuffix(name, lastFrameSuffix) }
+func LastFrameOrigKey(name string) string { return strings.TrimSuffix(name, lastFrameSuffix) }
+
+// extractVideoFrames pulls two stills from an mp4 via ffmpeg: the FIRST frame
+// downscaled for list thumbnails (≤thumbMaxDim) and the LAST frame at full
+// resolution. Callers treat this as best-effort — any missing ffmpeg or decode
+// failure just means the derived objects aren't stored.
+func extractVideoFrames(ctx context.Context, video []byte) (thumb, last []byte, err error) {
+	ffmpeg, err := exec.LookPath("ffmpeg")
+	if err != nil {
+		return nil, nil, errors.New("ffmpeg not installed")
+	}
+	dir, err := os.MkdirTemp("", "vidframes-*")
+	if err != nil {
+		return nil, nil, err
+	}
+	defer os.RemoveAll(dir)
+	in := filepath.Join(dir, "in.mp4")
+	if err := os.WriteFile(in, video, 0o600); err != nil {
+		return nil, nil, err
+	}
+
+	thumbPath := filepath.Join(dir, "thumb.jpg")
+	if out, err := exec.CommandContext(ctx, ffmpeg, "-y", "-i", in,
+		"-vf", fmt.Sprintf("scale='min(%d,iw)':-2", thumbMaxDim),
+		"-frames:v", "1", "-q:v", "4", thumbPath).CombinedOutput(); err != nil {
+		return nil, nil, fmt.Errorf("ffmpeg first frame: %v: %s", err, clipTail(out))
+	}
+	thumb, err = os.ReadFile(thumbPath)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	// -sseof seeks from the end; a tiny negative offset lands on the final
+	// frame(s). Some encodes have sparse keyframes near EOF, so fall back to a
+	// wider window before giving up (thumb alone is still useful).
+	lastPath := filepath.Join(dir, "last.jpg")
+	for _, off := range []string{"-0.1", "-1"} {
+		_ = exec.CommandContext(ctx, ffmpeg, "-y", "-sseof", off, "-i", in,
+			"-frames:v", "1", "-q:v", "2", "-update", "1", lastPath).Run()
+		if b, rerr := os.ReadFile(lastPath); rerr == nil && len(b) > 0 {
+			last = b
+			break
+		}
+	}
+	return thumb, last, nil
+}
+
+func clipTail(b []byte) string {
+	s := strings.TrimSpace(string(b))
+	if len(s) > 300 {
+		s = s[len(s)-300:]
+	}
+	return s
+}