diff --git a/supysonic/api/media.py b/supysonic/api/media.py
index 19c64ff..564610c 100644
--- a/supysonic/api/media.py
+++ b/supysonic/api/media.py
@@ -110,6 +110,8 @@ def stream_media():
 
         current_app.logger.info('Transcoding track {0.id} for user {1.id}. Source: {2} at {0.bitrate}kbps. Dest: {3} at {4}kbps'.format(res, request.user, src_suffix, dst_suffix, dst_bitrate))
         response = Response(transcode(), mimetype = dst_mimetype)
+        if estimateContentLength == 'true':
+            response.headers.add('Content-Length', dst_bitrate * 1000 * res.duration // 8)
     else:
         response = send_file(res.path, mimetype = dst_mimetype, conditional=True)
 
diff --git a/tests/api/test_transcoding.py b/tests/api/test_transcoding.py
index 78d8f85..0b3f959 100644
--- a/tests/api/test_transcoding.py
+++ b/tests/api/test_transcoding.py
@@ -44,7 +44,7 @@ class TranscodingTestCase(ApiTestBase):
         self._make_request('stream', { 'id': self.trackid, 'format': 'wat' }, error = 0)
 
     def test_direct_transcode(self):
-        rv = self._stream(maxBitRate = 96)
+        rv = self._stream(maxBitRate = 96, estimateContentLength = 'true')
         self.assertIn('tests/assets/folder/silence.mp3', rv.data)
         self.assertTrue(rv.data.endswith('96'))