diff --git a/pkg/stacker/duration_extractor_test.go b/pkg/stacker/duration_extractor_test.go
new file mode 100644
index 0000000..2c15b8f
--- /dev/null
+++ b/pkg/stacker/duration_extractor_test.go
@@ -0,0 +1,36 @@
+package stacker
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/majorfi/immich-stack/pkg/utils"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestDurationExtractor(t *testing.T) {
+	extractor, ok := getExtractor("duration")
+	require.True(t, ok, "duration extractor must be registered")
+
+	tests := []struct {
+		name string
+		body string
+		want string
+	}{
+		{name: "v2 string", body: `{"id":"1","duration":"0:00:12.500000"}`, want: "0:00:12.500000"},
+		{name: "v3 number", body: `{"id":"2","duration":1250}`, want: "1250"},
+		{name: "v3 null", body: `{"id":"3","duration":null}`, want: ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var a utils.TAsset
+			require.NoError(t, json.Unmarshal([]byte(tt.body), &a))
+
+			got, err := extractor(a, utils.TCriteria{})
+			require.NoError(t, err)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}
diff --git a/pkg/stacker/stacker_extractors.go b/pkg/stacker/stacker_extractors.go
index 52c0988..2a06b75 100644
--- a/pkg/stacker/stacker_extractors.go
+++ b/pkg/stacker/stacker_extractors.go
@@ -14,7 +14,7 @@ var extractors = map[string]func(asset utils.TAsset, c utils.TCriteria) (string,
 	"id":            func(a utils.TAsset, _ utils.TCriteria) (string, error) { return a.ID, nil },
 	"deviceAssetId": func(a utils.TAsset, _ utils.TCriteria) (string, error) { return a.DeviceAssetID, nil },
 	"deviceId":      func(a utils.TAsset, _ utils.TCriteria) (string, error) { return a.DeviceID, nil },
-	"duration":      func(a utils.TAsset, _ utils.TCriteria) (string, error) { return a.Duration, nil },
+	"duration":      func(a utils.TAsset, _ utils.TCriteria) (string, error) { return string(a.Duration), nil },
 	"fileCreatedAt": func(a utils.TAsset, c utils.TCriteria) (string, error) {
 		return extractTimeWithDelta(a.FileCreatedAt, c.Delta)
 	},
diff --git a/pkg/utils/types.go b/pkg/utils/types.go
index 22ac980..bb2e7d4 100644
--- a/pkg/utils/types.go
+++ b/pkg/utils/types.go
@@ -1,5 +1,35 @@
 package utils
 
+import (
+	"bytes"
+	"encoding/json"
+)
+
+// Duration accepts Immich's asset duration as a string (<= v2) or a number of ms (v3, issue #69).
+type Duration string
+
+func (d *Duration) UnmarshalJSON(data []byte) error {
+	data = bytes.TrimSpace(data)
+	if len(data) == 0 || string(data) == "null" {
+		*d = ""
+		return nil
+	}
+	if data[0] == '"' {
+		var s string
+		if err := json.Unmarshal(data, &s); err != nil {
+			return err
+		}
+		*d = Duration(s)
+		return nil
+	}
+	var n json.Number
+	if err := json.Unmarshal(data, &n); err != nil {
+		return err
+	}
+	*d = Duration(n.String())
+	return nil
+}
+
 /**************************************************************************************************
 ** TDelta represents a time delta configuration for comparing time-based values.
 ** It allows for a buffer when comparing timestamps.
@@ -83,7 +113,7 @@ type TAsset struct {
 	Type             string     `json:"type"`               // Asset type
 	UpdatedAt        string     `json:"updatedAt"`          // Last update time
 	Checksum         string     `json:"checksum"`           // File checksum
-	Duration         string     `json:"duration"`           // Duration (for videos)
+	Duration         Duration   `json:"duration"`           // Duration; string on Immich <= v2, ms number on v3
 	Stack            *TStack    `json:"stack,omitempty"`    // Associated stack if any
 	ExifInfo         *TExifInfo `json:"exifInfo,omitempty"` // Optional EXIF metadata (size, etc.)
 }
diff --git a/pkg/utils/types_test.go b/pkg/utils/types_test.go
new file mode 100644
index 0000000..c569c2b
--- /dev/null
+++ b/pkg/utils/types_test.go
@@ -0,0 +1,97 @@
+package utils
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestDurationUnmarshalJSON(t *testing.T) {
+	tests := []struct {
+		name    string
+		input   string
+		want    Duration
+		wantErr bool
+	}{
+		{name: "v2 string zero", input: `"0:00:00.000000"`, want: "0:00:00.000000"},
+		{name: "v2 string non-zero", input: `"0:00:12.500000"`, want: "0:00:12.500000"},
+		{name: "v3 number ms", input: `1250`, want: "1250"},
+		{name: "v3 number zero", input: `0`, want: "0"},
+		{name: "v3 number large", input: `32420`, want: "32420"},
+		{name: "v3 number fractional", input: `1250.5`, want: "1250.5"},
+		{name: "null", input: `null`, want: ""},
+		{name: "empty string", input: `""`, want: ""},
+		{name: "bool is invalid", input: `true`, wantErr: true},
+		{name: "object is invalid", input: `{}`, wantErr: true},
+		{name: "array is invalid", input: `[1]`, wantErr: true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var d Duration
+			err := json.Unmarshal([]byte(tt.input), &d)
+			if tt.wantErr {
+				if err == nil {
+					t.Fatalf("expected error unmarshaling %q, got none (value=%q)", tt.input, d)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("unexpected error unmarshaling %q: %v", tt.input, err)
+			}
+			if d != tt.want {
+				t.Fatalf("unmarshaling %q = %q, want %q", tt.input, d, tt.want)
+			}
+		})
+	}
+}
+
+func TestTAssetDurationV2AndV3(t *testing.T) {
+	tests := []struct {
+		name         string
+		body         string
+		wantDuration Duration
+	}{
+		{name: "v2 image string duration", body: `{"id":"a1","type":"IMAGE","duration":"0:00:00.000000"}`, wantDuration: "0:00:00.000000"},
+		{name: "v3 image null duration", body: `{"id":"a2","type":"IMAGE","duration":null}`, wantDuration: ""},
+		{name: "v3 animated gif number duration", body: `{"id":"a3","type":"IMAGE","duration":1250}`, wantDuration: "1250"},
+		{name: "v3 video number duration", body: `{"id":"a4","type":"VIDEO","duration":32420}`, wantDuration: "32420"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var a TAsset
+			if err := json.Unmarshal([]byte(tt.body), &a); err != nil {
+				t.Fatalf("decoding asset: %v", err)
+			}
+			if a.Duration != tt.wantDuration {
+				t.Fatalf("Duration = %q, want %q", a.Duration, tt.wantDuration)
+			}
+		})
+	}
+}
+
+func TestSearchResponseDecodeMixedDurations(t *testing.T) {
+	body := `{"assets":{"items":[
+		{"id":"1","type":"IMAGE","duration":null},
+		{"id":"2","type":"IMAGE","duration":"0:00:00.000000"},
+		{"id":"3","type":"IMAGE","duration":1250},
+		{"id":"4","type":"VIDEO","duration":32420}
+	],"nextPage":"2"}}`
+
+	var resp TSearchResponse
+	if err := json.Unmarshal([]byte(body), &resp); err != nil {
+		t.Fatalf("decoding search response: %v", err)
+	}
+	if got := len(resp.Assets.Items); got != 4 {
+		t.Fatalf("decoded %d items, want 4", got)
+	}
+	want := []Duration{"", "0:00:00.000000", "1250", "32420"}
+	for i, w := range want {
+		if resp.Assets.Items[i].Duration != w {
+			t.Fatalf("item %d Duration = %q, want %q", i, resp.Assets.Items[i].Duration, w)
+		}
+	}
+	if resp.Assets.NextPage != "2" {
+		t.Fatalf("NextPage = %q, want %q", resp.Assets.NextPage, "2")
+	}
+}