diff --git a/libavfilter/af_afade.c b/libavfilter/af_afade.c
index 35c653746d..a6805b50b1 100644
--- a/libavfilter/af_afade.c
+++ b/libavfilter/af_afade.c
@@ -50,18 +50,18 @@ enum CurveType { TRI, QSIN, ESIN, HSIN, LOG, PAR, QUA, CUB, SQU, CBR };
 static const AVOption afade_options[] = {
     { "type",         "set the fade direction",                      OFFSET(type),         AV_OPT_TYPE_INT,    {.i64 = 0    }, 0, 1, FLAGS, "type" },
     { "t",            "set the fade direction",                      OFFSET(type),         AV_OPT_TYPE_INT,    {.i64 = 0    }, 0, 1, FLAGS, "type" },
-    { "in",           NULL,                                          0,                    AV_OPT_TYPE_CONST,  {.i64 = 0    }, 0, 0, FLAGS, "type" },
-    { "out",          NULL,                                          0,                    AV_OPT_TYPE_CONST,  {.i64 = 1    }, 0, 0, FLAGS, "type" },
-    { "start_sample", "set expression of sample to start fading",    OFFSET(start_sample), AV_OPT_TYPE_INT64,  {.i64 = 0    }, 0, INT64_MAX, FLAGS },
-    { "ss",           "set expression of sample to start fading",    OFFSET(start_sample), AV_OPT_TYPE_INT64,  {.i64 = 0    }, 0, INT64_MAX, FLAGS },
-    { "nb_samples",   "set expression for fade duration in samples", OFFSET(nb_samples),   AV_OPT_TYPE_INT,    {.i64 = 44100}, 1, INT32_MAX, FLAGS },
-    { "ns",           "set expression for fade duration in samples", OFFSET(nb_samples),   AV_OPT_TYPE_INT,    {.i64 = 44100}, 1, INT32_MAX, FLAGS },
-    { "start_time",   "set expression of time to start fading",      OFFSET(start_time),   AV_OPT_TYPE_DURATION, {.i64 = 0. }, 0, INT32_MAX, FLAGS },
-    { "st",           "set expression of time to start fading",      OFFSET(start_time),   AV_OPT_TYPE_DURATION, {.i64 = 0. }, 0, INT32_MAX, FLAGS },
-    { "duration",     "set expression for fade duration",            OFFSET(duration),     AV_OPT_TYPE_DURATION, {.i64 = 0. }, 0, INT32_MAX, FLAGS },
-    { "d",            "set expression for fade duration",            OFFSET(duration),     AV_OPT_TYPE_DURATION, {.i64 = 0. }, 0, INT32_MAX, FLAGS },
-    { "curve",        "set expression for fade curve",               OFFSET(curve),        AV_OPT_TYPE_INT,    {.i64 = TRI  }, TRI, CBR, FLAGS, "curve" },
-    { "c",            "set expression for fade curve",               OFFSET(curve),        AV_OPT_TYPE_INT,    {.i64 = TRI  }, TRI, CBR, FLAGS, "curve" },
+    { "in",           "fade-in",                                     0,                    AV_OPT_TYPE_CONST,  {.i64 = 0    }, 0, 0, FLAGS, "type" },
+    { "out",          "fade-out",                                    0,                    AV_OPT_TYPE_CONST,  {.i64 = 1    }, 0, 0, FLAGS, "type" },
+    { "start_sample", "set number of first sample to start fading",  OFFSET(start_sample), AV_OPT_TYPE_INT64,  {.i64 = 0    }, 0, INT64_MAX, FLAGS },
+    { "ss",           "set number of first sample to start fading",  OFFSET(start_sample), AV_OPT_TYPE_INT64,  {.i64 = 0    }, 0, INT64_MAX, FLAGS },
+    { "nb_samples",   "set number of samples for fade duration",     OFFSET(nb_samples),   AV_OPT_TYPE_INT,    {.i64 = 44100}, 1, INT32_MAX, FLAGS },
+    { "ns",           "set number of samples for fade duration",     OFFSET(nb_samples),   AV_OPT_TYPE_INT,    {.i64 = 44100}, 1, INT32_MAX, FLAGS },
+    { "start_time",   "set time to start fading",                    OFFSET(start_time),   AV_OPT_TYPE_DURATION, {.i64 = 0. }, 0, INT32_MAX, FLAGS },
+    { "st",           "set time to start fading",                    OFFSET(start_time),   AV_OPT_TYPE_DURATION, {.i64 = 0. }, 0, INT32_MAX, FLAGS },
+    { "duration",     "set fade duration",                           OFFSET(duration),     AV_OPT_TYPE_DURATION, {.i64 = 0. }, 0, INT32_MAX, FLAGS },
+    { "d",            "set fade duration",                           OFFSET(duration),     AV_OPT_TYPE_DURATION, {.i64 = 0. }, 0, INT32_MAX, FLAGS },
+    { "curve",        "set fade curve type",                         OFFSET(curve),        AV_OPT_TYPE_INT,    {.i64 = TRI  }, TRI, CBR, FLAGS, "curve" },
+    { "c",            "set fade curve type",                         OFFSET(curve),        AV_OPT_TYPE_INT,    {.i64 = TRI  }, TRI, CBR, FLAGS, "curve" },
     { "tri",          "linear slope",                                0,                    AV_OPT_TYPE_CONST,  {.i64 = TRI  }, 0, 0, FLAGS, "curve" },
     { "qsin",         "quarter of sine wave",                        0,                    AV_OPT_TYPE_CONST,  {.i64 = QSIN }, 0, 0, FLAGS, "curve" },
     { "esin",         "exponential sine wave",                       0,                    AV_OPT_TYPE_CONST,  {.i64 = ESIN }, 0, 0, FLAGS, "curve" },