@@ -2141,6 +2141,17 @@ static av_cold int validate_options(AC3EncodeContext *s)

     s->bit_alloc.sr_code  = i % 3;

     s->bitstream_id       = s->eac3 ? 16 : 8 + s->bit_alloc.sr_shift;

+    /* select a default bit rate if not set by the user */

+    if (!avctx->bit_rate) {

+        switch (s->fbw_channels) {

+        case 1: avctx->bit_rate =  96000; break;

+        case 2: avctx->bit_rate = 192000; break;

+        case 3: avctx->bit_rate = 320000; break;

+        case 4: avctx->bit_rate = 384000; break;

+        case 5: avctx->bit_rate = 448000; break;

+        }

+    }

+

     /* validate bit rate */

     if (s->eac3) {

         int max_br, min_br, wpf, min_br_dist, min_br_code;

@@ -151,4 +151,5 @@ AVCodec ff_ac3_fixed_encoder = {

     .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),

     .priv_class = &ac3enc_class,

     .channel_layouts = ff_ac3_channel_layouts,

+    .defaults        = ac3_defaults,

 };

@@ -149,5 +149,6 @@ AVCodec ff_ac3_encoder = {

     .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),

     .priv_class = &ac3enc_class,

     .channel_layouts = ff_ac3_channel_layouts,

+    .defaults        = ac3_defaults,

 };

 #endif

@@ -20,6 +20,7 @@

  */

 #include "libavutil/opt.h"

+#include "internal.h"

 #include "ac3.h"

 #if AC3ENC_TYPE == AC3ENC_TYPE_AC3_FIXED

@@ -78,3 +79,8 @@ static const AVOption eac3_options[] = {

     {"auto", "Selected by the Encoder", 0, AV_OPT_TYPE_CONST, {.dbl = AC3ENC_OPT_AUTO }, INT_MIN, INT_MAX, AC3ENC_PARAM, "cpl_start_band"},

 {NULL}

 };

+

+static const AVCodecDefault ac3_defaults[] = {

+    { "b",  "0" },

+    { NULL }

+};

@@ -258,5 +258,6 @@ AVCodec ff_eac3_encoder = {

     .long_name       = NULL_IF_CONFIG_SMALL("ATSC A/52 E-AC-3"),

     .priv_class      = &eac3enc_class,

     .channel_layouts = ff_ac3_channel_layouts,

+    .defaults        = ac3_defaults,

 };

 #endif