private static unsafe void DrawWaves(ThumbnailsRenderContext ctx, MediaStream audioStream)
{
var height = 88;
var width = 88;
using var recorder = new SKPictureRecorder();
using var canvas = recorder.BeginRecording(SKRect.Create(width, height));
var columnCount = 88 * 2;
var columnWidth = (float)width / columnCount;
using var wavePaint = new SKPaint { Color = new SKColor(128, 128, 128, 76), StrokeWidth = columnWidth };
var totalSample = audioStream.SampleRate * audioStream.Duration;
var columnMaxSample = (int)(totalSample / columnCount);
var columns = new short[columnCount];
using var decoder = audioStream.CreateStreamDecoder();
using var filter = new AudioFormatFilter("sample_fmts=s16:channel_layouts=mono", audioStream, decoder);
filter.Build();
long sum = 0;
var n = 0;
var c = 0;
while (filter.MoveNext())
{
var frame = filter.Current.Value;
var p = (short *)frame->data[0];
for (var i = 0; i < frame->nb_samples; i++)
{
sum += SampleAbs(p[i]);
n++;
if (n == columnMaxSample && c < columnCount)
{
columns[c] = (short)(sum / n);
n = 0;
sum = 0;
c++;
}
}
}
for (var i = 0; i < columnCount; i++)
{
var h = Math.Max((float)columns[i] * height / short.MaxValue, 0.5f);
var x = i * columnWidth;
canvas.DrawLine(x, (height - h) / 2.0f, x, (height + h) / 2.0f, wavePaint);
}
_cachedWaveformDecorationImage ??= SKImage.FromEncodedData(ReadWaveformDecorationImage());
canvas.DrawImage(_cachedWaveformDecorationImage, SKRect.Create((width - 28) / 2.0f, (height - 36) / 2.0f, 28, 36));
using var picture = recorder.EndRecording();
ThumbnailUtils.DrawShadowView(
ctx,
new SkPictureView(
picture,
new SKSize(88, 88)));
}
