lavfi/aevalsrc: add option channel_layout

Allow to explicitly specify the channel layout to select.

doc/filters.texi

@@ -606,8 +606,9 @@ audio signal.
 
 It accepts the syntax: @var{exprs}[::@var{options}].
 @var{exprs} is a list of expressions separated by ":", one for each
-separate channel. The output channel layout depends on the number of
-provided expressions, up to 8 channels are supported.
+separate channel. In case the @var{channel_layout} is not
+specified, the selected channel layout depends on the number of
+provided expressions.
 
 @var{options} is an optional sequence of @var{key}=@var{value} pairs,
 separated by ":".
@@ -616,6 +617,10 @@ The description of the accepted options follows.
 
 @table @option
 
+@item channel_layout, c
+Set the channel layout. The number of channels in the specified layout
+must be equal to the number of specified expressions.
+
 @item duration, d
 Set the minimum duration of the sourced audio. See the function
 @code{av_parse_time()} for the accepted format.
@@ -666,6 +671,13 @@ Generate a sin signal with frequency of 440 Hz, set sample rate to
 aevalsrc="sin(440*2*PI*t)::s=8000"
 @end example
 
+@item
+Generate a two channels signal, specify the channel layout (Front
+Center + Back Center) explicitly:
+@example
+aevalsrc="sin(420*2*PI*t):cos(430*2*PI*t)::c=FC|BC"
+@end example
+
 @item
 Generate white noise:
 @example

libavfilter/asrc_aevalsrc.c

@@ -52,6 +52,7 @@ typedef struct {
     char *sample_rate_str;
     int sample_rate;
     int64_t chlayout;
+    char *chlayout_str;
     int nb_channels;
     int64_t pts;
     AVExpr *expr[8];
@@ -72,6 +73,8 @@ static const AVOption eval_options[]= {
     { "s",           "set the sample rate",                           OFFSET(sample_rate_str), AV_OPT_TYPE_STRING, {.str = "44100"}, CHAR_MIN, CHAR_MAX },
     { "duration",    "set audio duration", OFFSET(duration_str), AV_OPT_TYPE_STRING, {.str = NULL}, 0, 0 },
     { "d",           "set audio duration", OFFSET(duration_str), AV_OPT_TYPE_STRING, {.str = NULL}, 0, 0 },
+    { "channel_layout", "set channel layout", OFFSET(chlayout_str), AV_OPT_TYPE_STRING, {.str = NULL}, 0, 0 },
+    { "c",              "set channel layout", OFFSET(chlayout_str), AV_OPT_TYPE_STRING, {.str = NULL}, 0, 0 },
 {NULL},
 };
 
@@ -111,9 +114,28 @@ static int init(AVFilterContext *ctx, const char *args, void *opaque)
         }
         buf = NULL;
     }
+    eval->nb_channels = i;
+
+    if (bufptr && (ret = av_set_options_string(eval, bufptr, "=", ":")) < 0)
+        goto end;
+
+    if (eval->chlayout_str) {
+        int n;
+        ret = ff_parse_channel_layout(&eval->chlayout, eval->chlayout_str, ctx);
+        if (ret < 0)
+            goto end;
 
+        n = av_get_channel_layout_nb_channels(eval->chlayout);
+        if (n != eval->nb_channels) {
+            av_log(ctx, AV_LOG_ERROR,
+                   "Mismatch between the specified number of channels '%d' "
+                   "and the number of channels '%d' in the specified channel layout '%s'\n",
+                   eval->nb_channels, n, eval->chlayout_str);
+            ret = AVERROR(EINVAL);
+            goto end;
+        }
+    } else {
     /* guess channel layout from nb expressions/channels */
-    eval->nb_channels = i;
     eval->chlayout = av_get_default_channel_layout(eval->nb_channels);
     if (!eval->chlayout) {
         av_log(ctx, AV_LOG_ERROR, "Invalid number of channels '%d' provided\n",
@@ -121,9 +143,7 @@ static int init(AVFilterContext *ctx, const char *args, void *opaque)
         ret = AVERROR(EINVAL);
         goto end;
     }
-
-    if (bufptr && (ret = av_set_options_string(eval, bufptr, "=", ":")) < 0)
-        goto end;
+    }
 
     if ((ret = ff_parse_sample_rate(&eval->sample_rate, eval->sample_rate_str, ctx)))
         goto end;
@@ -153,6 +173,7 @@ static void uninit(AVFilterContext *ctx)
         av_expr_free(eval->expr[i]);
         eval->expr[i] = NULL;
     }
+    av_freep(&eval->chlayout_str);
     av_freep(&eval->duration_str);
     av_freep(&eval->sample_rate_str);
 }

libavfilter/version.h

@@ -30,7 +30,7 @@
 
 #define LIBAVFILTER_VERSION_MAJOR  2
 #define LIBAVFILTER_VERSION_MINOR 74
-#define LIBAVFILTER_VERSION_MICRO 100
+#define LIBAVFILTER_VERSION_MICRO 101
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
                                                LIBAVFILTER_VERSION_MINOR, \