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avfilter/avf_showspectrum: rewrite frequency log axis/bin scaling

This commit is contained in:
Paul B Mahol 2021-09-19 22:27:07 +02:00
parent 60ada0f5fa
commit 59719a905c
1 changed files with 35 additions and 57 deletions
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92
libavfilter/avf_showspectrum.c
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@ -645,54 +645,37 @@ static char *get_time(AVFilterContext *ctx, float seconds, int x)
return units; return units;
} }
static float log_scale(const float value, const float min, const float max) static float log_scale(const float bin,
const float bmin, const float bmax,
const float min, const float max)
{ {
if (value < min) return exp2f(((bin - bmin) / (bmax - bmin)) * (log2f(max) - log2f(min)) + log2f(min));
return min; }
if (value > max)
return max;
{ static float get_hz(const float bin, const float bmax,
const float b = logf(max / min) / (max - min); const float min, const float max,
const float a = max / expf(max * b); int fscale)
{
return expf(value * b) * a; switch (fscale) {
case F_LINEAR:
return min + (bin / bmax) * (max - min);
case F_LOG:
return min + log_scale(bin, 0, bmax, 20.f, max - min);
default:
return 0.f;
} }
} }
static float get_log_hz(const int bin, const int num_bins, const float sample_rate) static float inv_log_scale(float bin,
float bmin, float bmax,
float min, float max)
{ {
const float max_freq = sample_rate / 2; return (min * exp2f((bin * (log2f(max) - log2f(20.f))) / bmax) + min) * bmax / max;
const float hz_per_bin = max_freq / num_bins;
const float freq = hz_per_bin * bin;
const float scaled_freq = log_scale(freq + 1, 21, max_freq) - 1;
return num_bins * scaled_freq / max_freq;
} }
static float inv_log_scale(const float value, const float min, const float max) static float bin_pos(const int bin, const int num_bins, const float min, const float max)
{ {
if (value < min) return inv_log_scale(bin, 0.f, num_bins, 20.f, max - min);
return min;
if (value > max)
return max;
{
const float b = logf(max / min) / (max - min);
const float a = max / expf(max * b);
return logf(value / a) / b;
}
}
static float bin_pos(const int bin, const int num_bins, const float sample_rate)
{
const float max_freq = sample_rate / 2;
const float hz_per_bin = max_freq / num_bins;
const float freq = hz_per_bin * bin;
const float scaled_freq = inv_log_scale(freq + 1, 21, max_freq) - 1;
return num_bins * scaled_freq / max_freq;
} }
static float get_scale(AVFilterContext *ctx, int scale, float a) static float get_scale(AVFilterContext *ctx, int scale, float a)
@ -835,8 +818,7 @@ static int draw_legend(AVFilterContext *ctx, int samples)
} }
for (y = 0; y < h; y += 40) { for (y = 0; y < h; y += 40) {
float range = s->stop ? s->stop - s->start : inlink->sample_rate / 2; float range = s->stop ? s->stop - s->start : inlink->sample_rate / 2;
float bin = s->fscale == F_LINEAR ? y : get_log_hz(y, h, inlink->sample_rate); float hertz = get_hz(y, h, s->start, s->start + range, s->fscale);
float hertz = s->start + bin * range / (float)h;
char *units; char *units;
if (hertz == 0) if (hertz == 0)
@ -893,8 +875,7 @@ static int draw_legend(AVFilterContext *ctx, int samples)
} }
for (x = 0; x < w - 79; x += 80) { for (x = 0; x < w - 79; x += 80) {
float range = s->stop ? s->stop - s->start : inlink->sample_rate / 2; float range = s->stop ? s->stop - s->start : inlink->sample_rate / 2;
float bin = s->fscale == F_LINEAR ? x : get_log_hz(x, w, inlink->sample_rate); float hertz = get_hz(x, w, s->start, s->start + range, s->fscale);
float hertz = s->start + bin * range / (float)w;
char *units; char *units;
if (hertz == 0) if (hertz == 0)
@ -1019,29 +1000,26 @@ static int plot_channel_log(AVFilterContext *ctx, void *arg, int jobnr, int nb_j
AVFilterLink *inlink = ctx->inputs[0]; AVFilterLink *inlink = ctx->inputs[0];
const int h = s->orientation == VERTICAL ? s->channel_height : s->channel_width; const int h = s->orientation == VERTICAL ? s->channel_height : s->channel_width;
const int ch = jobnr; const int ch = jobnr;
float y, yf, uf, vf; float yf, uf, vf;
int yy = 0;
/* decide color range */ /* decide color range */
color_range(s, ch, &yf, &uf, &vf); color_range(s, ch, &yf, &uf, &vf);
/* draw the channel */ /* draw the channel */
for (y = 0; y < h && yy < h; yy++) { for (int yy = 0; yy < h; yy++) {
float pos0 = bin_pos(yy+0, h, inlink->sample_rate); float range = s->stop ? s->stop - s->start : inlink->sample_rate / 2;
float pos1 = bin_pos(yy+1, h, inlink->sample_rate); float pos = bin_pos(yy, h, s->start, s->start + range);
float delta = pos1 - pos0; float delta = pos - floorf(pos);
float a0, a1; float a0, a1;
a0 = get_value(ctx, ch, yy+0); a0 = get_value(ctx, ch, av_clip(pos, 0, h-1));
a1 = get_value(ctx, ch, FFMIN(yy+1, h-1)); a1 = get_value(ctx, ch, av_clip(pos+1, 0, h-1));
for (float j = pos0; j < pos1 && y + j - pos0 < h; j++) { {
float row = (s->mode == COMBINED) ? av_clipf(y + j - pos0, 0, h - 1) : ch * h + av_clipf(y + j - pos0, 0, h - 1); int row = (s->mode == COMBINED) ? yy : ch * h + yy;
float *out = &s->color_buffer[ch][3 * lrintf(row)]; float *out = &s->color_buffer[ch][3 * row];
float lerpfrac = (j - pos0) / delta;
pick_color(s, yf, uf, vf, lerpfrac * a1 + (1.f-lerpfrac) * a0, out); pick_color(s, yf, uf, vf, delta * a1 + (1.f - delta) * a0, out);
} }
y += delta;
} }
return 0; return 0;