.mp4 output via FFmpeg fails.

[ailgun]

Hello, I'm trying to use a code as below to create a .mp4 file (it's by someone else but I just wanted to try it out). It should create a mp4 file but after it creates a temp folder containing all the png frames and it gets deleted as expected after the process is finished - but it leaves no .mp4 file behind.

I also installed ffmpeg via pip install.

I wonder what I might be doing wrong?

Thanks!

import scipy.misc
import os

cols, rows = 10, 4
nf = 24  # num frames per transitions
ni = 4   # num transitions

folder='temp'
os.makedirs(folder)
os.makedirs('%s/composite'%folder)
print("generating frames for individual faces")
for i in tqdm(range(cols)):
    for j in range(rows):
        idx = np.random.randint(n, size=ni)
        idx = np.append(idx, idx[0])
        f = 1
        for k in range(ni):
            xp1, xp2 = Xp[idx[k]], Xp[idx[k+1]]
            Z = [[(1.0-r)*i1 + r*i2 for i1, i2 in zip(xp1, xp2)] for r in np.linspace(0,1,nf)]
            Y = [ np.clip(pca.inverse_transform(z),0,255).reshape((w,h,3)) for z in Z ]
            for y in Y:
                scipy.misc.imsave('%s/face%02d_%02d_frame%04d.png'%(folder,i,j,f), y.astype('uint8'))
                f+=1
offset = np.random.randint(nf*(ni-1), size=cols*rows)
print("compositing all the faces into one video")
for f in tqdm(range(nf*ni)):
    img = Image.new('RGB',(w * cols, h * rows))
    for i in range(cols):
        for j in range(rows):
            fidx = 1+(f + offset[i*rows+j])%(nf*ni)
            im = Image.open('%s/face%02d_%02d_frame%04d.png'%(folder,i,j,fidx))
            img.paste(im, (i*w, j*h))
    img = img.resize((int(1.2*img.size[0]), int(1.2*img.size[1]))) #upscale just a bit
    scipy.misc.imsave('temp/composite/frame%04d.png'%f, img)
cmd = "ffmpeg -i %s/composite/frame%%04d.png -c:v libx264 -pix_fmt yuv420p composite.mp4"%folder
print(cmd)
os.system(cmd)
os.system("rm -rf %s"%folder)
print("done!")