如何从波形中提取频率

Question

我正在尝试从mp4文件中两行之间的位移中提取频率，但是看起来出了点问题。

首先，我将视频转换为帧，并找到每帧两行之间的距离，然后对其应用FFT，最后找到幅度。

由于输出未接近实际值，似乎我做错了事。

clear all
clc

reader = VideoReader('2.mp4');
nof = reader.NumberOfFrames;
refp = zeros(nof,2);
oscp = zeros(nof,2);

reader = VideoReader('2.mp4');
ii = 1;

while hasFrame(reader)
    frame = readFrame(reader);
    redc = frame(:,:,1);
    redc = redc > 150;
    redc = imopen(redc, ones(5));
    props = regionprops(redc,'FilledArea','Centroid');

    nob = length(props);
    if (nob > 1)
        blobs = zeros(nob,1);
        for jj = 1 : nob
            blobs(jj) = props(jj).FilledArea;
        end
        blobs = sort(blobs);
        for jj = 1 : nob
            if (props(jj).FilledArea == blobs(1))
                ind1 = jj;
            end
            if (props(jj).FilledArea == blobs(2))
                ind2 = jj;
            end
        end

        if (props(ind1).Centroid < props(ind2).Centroid)
            refp(ii,:) = props(ind1).Centroid;
            oscp(ii,:) = props(ind2).Centroid;
        else
            refp(ii,:) = props(ind2).Centroid;
            oscp(ii,:) = props(ind1).Centroid;
        end
    else
        if (ii > 1)
            refp(ii,:) = refp(ii-1,:);
            oscp(ii,:) = oscp(ii-1,:);
        end
    end
    ii = ii + 1;

%     subplot(1,2,1)
%     imshow(frame,[]);
%     title('RGB Frame')
%     subplot(1,2,2)
%     imshow(redc,[]);
%     title('Thresholded Red Channel')
%     pause(0.05);
end

dist = sqrt((oscp(:,1) - refp(:,1)).^2 + (oscp(:,2) - refp(:,2)).^2);
t = 1:length(dist);
t = t / reader.FrameRate;

figure
plot(t,dist,'r','LineWidth',1.5)
grid minor
title('Oscillations');
% xlim([160,210]);
% ylim([5,inf])
xlabel('Frame Number');
ylabel('Distance (Pixels)');

fdist = fftshift(fft(dist));
fs = reader.FrameRate;
f = fs * (0:length(fdist)-1) / length(fdist);
[m,ind] = max(abs(fdist));

figure
subplot(2,1,1)
plot(f,abs(fdist),'m','LineWidth',1.5);
grid minor
title('FFT (Magnitude)')
xlabel('Frequency (Hz)')
ylabel('Magnitude')

text(f(ind) + 1, abs(fdist(ind)), sprintf('Frequency = %f ',f(ind)));
text(f(ind) + 1, abs(fdist(ind))-30000, sprintf('Amplitude = %f ',abs(fdist(ind))));

subplot(2,1,2)
plot(f,angle(fdist),'Color',[1,0.5,0],'LineWidth',1.5);
grid minor
title('FFT (Phase)');
xlabel('Frequency (Hz)');

waveform and FFT Video sample