ac3enc: allow Dolby Pro Logic II as a preferred downmix mode.

Some encoders already use this value even
though it's reserved in the A/52 specification.

libavcodec/ac3enc.h

@@ -86,6 +86,7 @@ typedef int64_t CoefSumType;
 #define AC3ENC_OPT_SMALL_ROOM       2
 #define AC3ENC_OPT_DOWNMIX_LTRT     1
 #define AC3ENC_OPT_DOWNMIX_LORO     2
+#define AC3ENC_OPT_DOWNMIX_DPLII    3 // reserved value in A/52, but used by encoders to indicate DPL2
 #define AC3ENC_OPT_ADCONV_STANDARD  0
 #define AC3ENC_OPT_ADCONV_HDCD      1
 

libavcodec/ac3enc_opts_template.c

@@ -46,10 +46,11 @@ static const AVOption ac3_options[] = {
     {"off",          "Not Dolby Surround Encoded", 0, AV_OPT_TYPE_CONST, {.i64 = AC3ENC_OPT_MODE_OFF      }, INT_MIN, INT_MAX, AC3ENC_PARAM, "dsur_mode"},
 {"original", "Original Bit Stream", OFFSET(original), AV_OPT_TYPE_INT,   {.i64 = AC3ENC_OPT_NONE }, AC3ENC_OPT_NONE, 1, AC3ENC_PARAM},
 /* extended bitstream information */
-{"dmix_mode", "Preferred Stereo Downmix Mode", OFFSET(preferred_stereo_downmix), AV_OPT_TYPE_INT, {.i64 = AC3ENC_OPT_NONE }, AC3ENC_OPT_NONE, AC3ENC_OPT_DOWNMIX_LORO, AC3ENC_PARAM, "dmix_mode"},
+{"dmix_mode", "Preferred Stereo Downmix Mode", OFFSET(preferred_stereo_downmix), AV_OPT_TYPE_INT, {.i64 = AC3ENC_OPT_NONE }, AC3ENC_OPT_NONE, AC3ENC_OPT_DOWNMIX_DPLII, AC3ENC_PARAM, "dmix_mode"},
     {"notindicated", "Not Indicated (default)", 0, AV_OPT_TYPE_CONST, {.i64 = AC3ENC_OPT_NOT_INDICATED }, INT_MIN, INT_MAX, AC3ENC_PARAM, "dmix_mode"},
     {"ltrt", "Lt/Rt Downmix Preferred",         0, AV_OPT_TYPE_CONST, {.i64 = AC3ENC_OPT_DOWNMIX_LTRT  }, INT_MIN, INT_MAX, AC3ENC_PARAM, "dmix_mode"},
     {"loro", "Lo/Ro Downmix Preferred",         0, AV_OPT_TYPE_CONST, {.i64 = AC3ENC_OPT_DOWNMIX_LORO  }, INT_MIN, INT_MAX, AC3ENC_PARAM, "dmix_mode"},
+    {"dplii", "Dolby Pro Logic II Downmix Preferred", 0, AV_OPT_TYPE_CONST, {.i64 = AC3ENC_OPT_DOWNMIX_DPLII }, INT_MIN, INT_MAX, AC3ENC_PARAM, "dmix_mode"},
 {"ltrt_cmixlev", "Lt/Rt Center Mix Level", OFFSET(ltrt_center_mix_level), AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, AC3ENC_PARAM},
 {"ltrt_surmixlev", "Lt/Rt Surround Mix Level", OFFSET(ltrt_surround_mix_level), AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, AC3ENC_PARAM},
 {"loro_cmixlev", "Lo/Ro Center Mix Level", OFFSET(loro_center_mix_level), AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, AC3ENC_PARAM},