diff --git a/libavformat/isom.c b/libavformat/isom.c
index ba952b826e8bbaca5124b598a695e17c0b6eba4c..f7540ebb558db9f054827bf270b3acda055a1fe6 100644
--- a/libavformat/isom.c
+++ b/libavformat/isom.c
@@ -300,7 +300,7 @@ const AVCodecTag ff_codec_movaudio_tags[] = {
     { AV_CODEC_ID_QDM2,            MKTAG('Q', 'D', 'M', '2') },
     { AV_CODEC_ID_QDMC,            MKTAG('Q', 'D', 'M', 'C') },
     { AV_CODEC_ID_SPEEX,           MKTAG('s', 'p', 'e', 'x') }, /* Flash Media Server */
-    { AV_CODEC_ID_SPEEX,           MKTAG('S', 'P', 'X', 'N') },
+    { AV_CODEC_ID_SPEEX,           MKTAG('S', 'P', 'X', 'N') }, /* ZygoAudio (quality 10 mode) */
     { AV_CODEC_ID_WMAV2,           MKTAG('W', 'M', 'A', '2') },
     { AV_CODEC_ID_EVRC,            MKTAG('s', 'e', 'v', 'c') }, /* 3GPP2 */
     { AV_CODEC_ID_SMV,             MKTAG('s', 's', 'm', 'v') }, /* 3GPP2 */