feat(subsonic): support timeOffset in stream.view (#384)

as per
https://github.com/opensubsonic/open-subsonic-api/pull/54
https://github.com/opensubsonic/open-subsonic-api/discussions/21

dont cache partial transcodes

add a transcode seek test

transcode/transcode_test.go

@@ -64,3 +64,39 @@ func TestTranscode(t *testing.T) {
 	// we should have 5 seconds of PCM data
 	require.Equal(t, testFileLen*bytesPerSec, buf.Len())
 }
+
+// TestTranscodeWithSeek starts a web server that transcodes a 5s FLAC file to PCM audio, but with a 2 second offset.
+// A client consumes the result over a 3 second period.
+func TestTranscodeWithSeek(t *testing.T) {
+	t.Parallel()
+
+	testFile := "testdata/5s.flac"
+	testFileLen := 5
+
+	seekSecs := 2
+	profile := transcode.WithSeek(testProfile, time.Duration(seekSecs)*time.Second)
+
+	tr := transcode.NewFFmpegTranscoder()
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		require.NoError(t, tr.Transcode(r.Context(), profile, testFile, w))
+		w.(http.Flusher).Flush()
+	}))
+	defer server.Close()
+
+	resp, err := server.Client().Get(server.URL)
+	require.NoError(t, err)
+	defer resp.Body.Close()
+
+	var buf bytes.Buffer
+	for {
+		n, err := io.Copy(&buf, io.LimitReader(resp.Body, bytesPerSec))
+		require.NoError(t, err)
+		if n == 0 {
+			break
+		}
+		time.Sleep(1 * time.Second)
+	}
+
+	// since we seeked 2 seconds, we should have 5-2 = 3 seconds of PCM data
+	require.Equal(t, (testFileLen-seekSecs)*bytesPerSec, buf.Len())
+}