fix(thumbnails): pick audio cover art deterministically

go.mod

@@ -412,3 +412,5 @@ replace go-micro.dev/v4 => github.com/butonic/go-micro/v4 v4.11.1-0.202411151126
 exclude github.com/mattn/go-sqlite3 v2.0.3+incompatible
 
 replace github.com/go-micro/plugins/v4/store/nats-js-kv => github.com/opencloud-eu/go-micro-plugins/v4/store/nats-js-kv v0.0.0-20250512152754-23325793059a
+
+replace github.com/dhowden/tag => github.com/dschmidt/tag v0.0.0-20260730135516-8eb6fc4a6973

go.sum

@@ -297,8 +297,6 @@ github.com/dgryski/go-rendezvous v0.0.0-20200823014737-9f7001d12a5f/go.mod h1:cu
 github.com/dgryski/go-sip13 v0.0.0-20181026042036-e10d5fee7954/go.mod h1:vAd38F8PWV+bWy6jNmig1y/TA+kYO4g3RSRF0IAv0no=
 github.com/dgryski/trifles v0.0.0-20230903005119-f50d829f2e54 h1:SG7nF6SRlWhcT7cNTs5R6Hk4V2lcmLz2NsG2VnInyNo=
 github.com/dgryski/trifles v0.0.0-20230903005119-f50d829f2e54/go.mod h1:if7Fbed8SFyPtHLHbg49SI7NAdJiC5WIA09pe59rfAA=
-github.com/dhowden/tag v0.0.0-20240417053706-3d75831295e8 h1:OtSeLS5y0Uy01jaKK4mA/WVIYtpzVm63vLVAPzJXigg=
-github.com/dhowden/tag v0.0.0-20240417053706-3d75831295e8/go.mod h1:apkPC/CR3s48O2D7Y++n1XWEpgPNNCjXYga3PPbJe2E=
 github.com/dimchansky/utfbom v1.1.0/go.mod h1:rO41eb7gLfo8SF1jd9F8HplJm1Fewwi4mQvIirEdv+8=
 github.com/distribution/reference v0.6.0 h1:0IXCQ5g4/QMHHkarYzh5l+u8T3t73zM5QvfrDyIgxBk=
 github.com/distribution/reference v0.6.0/go.mod h1:BbU0aIcezP1/5jX/8MP0YiH4SdvB5Y4f/wlDRiLyi3E=
@@ -310,6 +308,8 @@ github.com/docker/go-connections v0.6.0 h1:LlMG9azAe1TqfR7sO+NJttz1gy6KO7VJBh+pM
 github.com/docker/go-connections v0.6.0/go.mod h1:AahvXYshr6JgfUJGdDCs2b5EZG/vmaMAntpSFH5BFKE=
 github.com/docker/go-units v0.5.0 h1:69rxXcBk27SvSaaxTtLh/8llcHD8vYHT7WSdRZ/jvr4=
 github.com/docker/go-units v0.5.0/go.mod h1:fgPhTUdO+D/Jk86RDLlptpiXQzgHJF7gydDDbaIK4Dk=
+github.com/dschmidt/tag v0.0.0-20260730135516-8eb6fc4a6973 h1:XnAwTTbblPJI6OVkRwqVA2MGjre29B/+wsi16lQfJ+E=
+github.com/dschmidt/tag v0.0.0-20260730135516-8eb6fc4a6973/go.mod h1:apkPC/CR3s48O2D7Y++n1XWEpgPNNCjXYga3PPbJe2E=
 github.com/dustin/go-humanize v1.0.1 h1:GzkhY7T5VNhEkwH0PVJgjz+fX1rhBrR7pRT3mDkpeCY=
 github.com/dustin/go-humanize v1.0.1/go.mod h1:Mu1zIs6XwVuF/gI1OepvI0qD18qycQx+mFykh5fBlto=
 github.com/dutchcoders/go-clamd v0.0.0-20170520113014-b970184f4d9e h1:rcHHSQqzCgvlwP0I/fQ8rQMn/MpHE5gWSLdtpxtP6KQ=

services/thumbnails/pkg/preprocessor/preprocessor.go

@@ -89,7 +89,7 @@ func (i AudioDecoder) Convert(r io.Reader) (any, error) {
 		return nil, err
 	}
 
-	picture := m.Picture()
+	picture := selectCoverArt(m.Pictures())
 	if picture == nil {
 		return nil, thumbnailerErrors.ErrNoImageFromAudioFile
 	}
@@ -102,6 +102,27 @@ func (i AudioDecoder) Convert(r io.Reader) (any, error) {
 	return converter.Convert(bytes.NewReader(picture.Data))
 }
 
+// frontCoverType is the ID3/APIC picture type byte for a front cover, shared by
+// the ID3v2, FLAC and OGG tag formats (see github.com/dhowden/tag pictureTypes).
+const frontCoverType byte = 0x03
+
+// selectCoverArt deterministically picks the cover art from an audio file's
+// embedded pictures: the explicitly tagged front cover if present, otherwise
+// the first available picture. Many taggers store the cover as type "Other"
+// (0x00) instead of "Cover (front)" (0x03), so the fallback is the common case.
+// It returns nil when there are no pictures.
+func selectCoverArt(pictures []tag.Picture) *tag.Picture {
+	if len(pictures) == 0 {
+		return nil
+	}
+	for i := range pictures {
+		if pictures[i].RawType == frontCoverType {
+			return &pictures[i]
+		}
+	}
+	return &pictures[0]
+}
+
 // TxtToImageConverter is a converter for the text file
 type TxtToImageConverter struct {
 	fontLoader *FontLoader

services/thumbnails/pkg/preprocessor/preprocessor_test.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"testing"
 
+	"github.com/dhowden/tag"
 	"golang.org/x/image/font"
 	"golang.org/x/image/font/opentype"
 
@@ -127,6 +128,28 @@ var _ = Describe("ImageDecoder", func() {
 		})
 	})
 
+	Describe("selectCoverArt", func() {
+		front := tag.Picture{RawType: frontCoverType, MIMEType: "image/jpeg", Data: []byte("front")}
+		back := tag.Picture{RawType: 0x04, MIMEType: "image/jpeg", Data: []byte("back")}
+		other := tag.Picture{RawType: 0x00, MIMEType: "image/png", Data: []byte("other")}
+
+		It("returns nil when there are no pictures", func() {
+			Expect(selectCoverArt(nil)).To(BeNil())
+			Expect(selectCoverArt([]tag.Picture{})).To(BeNil())
+		})
+		It("prefers the front cover regardless of order", func() {
+			got := selectCoverArt([]tag.Picture{back, other, front})
+			Expect(got).ToNot(BeNil())
+			Expect(got.RawType).To(Equal(frontCoverType))
+			Expect(got.Data).To(Equal([]byte("front")))
+		})
+		It("falls back to the first picture when none is a front cover", func() {
+			got := selectCoverArt([]tag.Picture{other, back})
+			Expect(got).ToNot(BeNil())
+			Expect(got.Data).To(Equal([]byte("other")))
+		})
+	})
+
 	Describe("should decode text", func() {
 		var decoder TxtToImageConverter
 		BeforeEach(func() {

vendor/modules.txt

@@ -373,7 +373,7 @@ github.com/dgraph-io/ristretto/z/simd
 # github.com/dgryski/go-rendezvous v0.0.0-20200823014737-9f7001d12a5f
 ## explicit
 github.com/dgryski/go-rendezvous
-# github.com/dhowden/tag v0.0.0-20240417053706-3d75831295e8
+# github.com/dhowden/tag v0.0.0-20240417053706-3d75831295e8 => github.com/dschmidt/tag v0.0.0-20260730135516-8eb6fc4a6973
 ## explicit; go 1.20
 github.com/dhowden/tag
 # github.com/distribution/reference v0.6.0
@@ -2738,3 +2738,4 @@ stash.kopano.io/kgol/rndm
 # github.com/unrolled/secure => github.com/opencloud-eu/secure v0.0.0-20260312082735-b6f5cb2244e4
 # go-micro.dev/v4 => github.com/butonic/go-micro/v4 v4.11.1-0.20241115112658-b5d4de5ed9b3
 # github.com/go-micro/plugins/v4/store/nats-js-kv => github.com/opencloud-eu/go-micro-plugins/v4/store/nats-js-kv v0.0.0-20250512152754-23325793059a
+# github.com/dhowden/tag => github.com/dschmidt/tag v0.0.0-20260730135516-8eb6fc4a6973