avfilter/avf_showfreqs: make selecting window size simpler

The previous solution was very bad.

doc/filters.texi

@@ -22346,25 +22346,9 @@ Reverse logarithmic scale.
 Default is @code{lin}.
 
 @item win_size
-Set window size.
+Set window size. Allowed range is from 16 to 65536.
 
-It accepts the following values:
-@table @samp
-@item w16
-@item w32
-@item w64
-@item w128
-@item w256
-@item w512
-@item w1024
-@item w2048
-@item w4096
-@item w8192
-@item w16384
-@item w32768
-@item w65536
-@end table
-Default is @code{w2048}
+Default is @code{2048}
 
 @item win_func
 Set windowing function.

libavfilter/avf_showfreqs.c

@@ -46,6 +46,7 @@ typedef struct ShowFreqsContext {
     int w, h;
     int mode;
     int cmode;
+    int fft_size;
     int fft_bits;
     int ascale, fscale;
     int avg;
@@ -85,20 +86,7 @@ static const AVOption showfreqs_options[] = {
         { "lin",  "linear",              0, AV_OPT_TYPE_CONST, {.i64=FS_LINEAR}, 0, 0, FLAGS, "fscale" },
         { "log",  "logarithmic",         0, AV_OPT_TYPE_CONST, {.i64=FS_LOG},    0, 0, FLAGS, "fscale" },
         { "rlog", "reverse logarithmic", 0, AV_OPT_TYPE_CONST, {.i64=FS_RLOG},   0, 0, FLAGS, "fscale" },
-    { "win_size", "set window size", OFFSET(fft_bits), AV_OPT_TYPE_INT, {.i64=11}, 4, 16, FLAGS, "fft" },
-        { "w16",    0, 0, AV_OPT_TYPE_CONST, {.i64=4},  0, 0, FLAGS, "fft" },
-        { "w32",    0, 0, AV_OPT_TYPE_CONST, {.i64=5},  0, 0, FLAGS, "fft" },
-        { "w64",    0, 0, AV_OPT_TYPE_CONST, {.i64=6},  0, 0, FLAGS, "fft" },
-        { "w128",   0, 0, AV_OPT_TYPE_CONST, {.i64=7},  0, 0, FLAGS, "fft" },
-        { "w256",   0, 0, AV_OPT_TYPE_CONST, {.i64=8},  0, 0, FLAGS, "fft" },
-        { "w512",   0, 0, AV_OPT_TYPE_CONST, {.i64=9},  0, 0, FLAGS, "fft" },
-        { "w1024",  0, 0, AV_OPT_TYPE_CONST, {.i64=10}, 0, 0, FLAGS, "fft" },
-        { "w2048",  0, 0, AV_OPT_TYPE_CONST, {.i64=11}, 0, 0, FLAGS, "fft" },
-        { "w4096",  0, 0, AV_OPT_TYPE_CONST, {.i64=12}, 0, 0, FLAGS, "fft" },
-        { "w8192",  0, 0, AV_OPT_TYPE_CONST, {.i64=13}, 0, 0, FLAGS, "fft" },
-        { "w16384", 0, 0, AV_OPT_TYPE_CONST, {.i64=14}, 0, 0, FLAGS, "fft" },
-        { "w32768", 0, 0, AV_OPT_TYPE_CONST, {.i64=15}, 0, 0, FLAGS, "fft" },
-        { "w65536", 0, 0, AV_OPT_TYPE_CONST, {.i64=16}, 0, 0, FLAGS, "fft" },
+    { "win_size", "set window size", OFFSET(fft_size), AV_OPT_TYPE_INT, {.i64=2048}, 16, 65536, FLAGS },
     { "win_func", "set window function", OFFSET(win_func), AV_OPT_TYPE_INT, {.i64=WFUNC_HANNING}, 0, NB_WFUNC-1, FLAGS, "win_func" },
         { "rect",     "Rectangular",      0, AV_OPT_TYPE_CONST, {.i64=WFUNC_RECT},     0, 0, FLAGS, "win_func" },
         { "bartlett", "Bartlett",         0, AV_OPT_TYPE_CONST, {.i64=WFUNC_BARTLETT}, 0, 0, FLAGS, "win_func" },
@@ -180,6 +168,7 @@ static int config_output(AVFilterLink *outlink)
     float overlap;
     int i;
 
+    s->fft_bits = av_log2(s->fft_size);
     s->nb_freq = 1 << (s->fft_bits - 1);
     s->win_size = s->nb_freq << 1;
     av_audio_fifo_free(s->fifo);