fix(stream): compute the estimated content length in kilobits of 1000 bits

estimateContentLength=true announced Duration * bitRate / 8 * 1024 bytes, but a
bitrate in kbps is 1000 bits per second, so the header overstated the body by
2.4%. A client that trusts it waits for bytes that never arrive: on a 285s track
at 128kbps it asked for 4,669,440 bytes of a 4,561,876 byte body.

Reported in #6170.

core/stream/media_streamer.go

@@ -147,7 +147,7 @@ func (s *Stream) ContentType() string { return mime.TypeByExtension("." + s.form
 func (s *Stream) Name() string        { return s.mf.Title + "." + s.format }
 func (s *Stream) ModTime() time.Time  { return s.mf.UpdatedAt }
 func (s *Stream) EstimatedContentLength() int {
-	return int(s.mf.Duration * float32(s.bitRate) / 8 * 1024)
+	return int(s.mf.Duration * float32(s.bitRate) / 8 * 1000)
 }
 
 // Serve writes the stream to the HTTP response. For seekable streams it uses http.ServeContent

core/stream/media_streamer_test.go

@@ -183,6 +183,18 @@ var _ = Describe("MediaStreamer", func() {
 			_, err = io.ReadAll(resp.Body)
 			Expect(err).To(HaveOccurred())
 		})
+
+		It("estimates the content length from a bitrate in kilobits of 1000 bits", func() {
+			hundredSeconds := *mf
+			hundredSeconds.Duration = 100
+			s := stream.NewStream(&hundredSeconds, "mp3", 128, io.NopCloser(bytes.NewReader(nil)))
+			w := httptest.NewRecorder()
+			r := httptest.NewRequest(http.MethodGet, "/?estimateContentLength=true", nil)
+
+			_, _ = s.Serve(ctx, w, r)
+
+			Expect(w.Header().Get("Content-Length")).To(Equal("1600000"))
+		})
 	})
 })