Creating a video from multiple png files using ffmpeg

To make videos we’re going to use the ffmpeg command line tool. This is installed as an Mac OS executable and isn’t part of Python.

We’ll need ffmpeg installed correctly. If not installed already you can use brew install ffmpeg to get it. You can also use brew update && brew upgrade to update it. This does take a little while to download and install.

For our test I’m going to use the images created in the last post

!ls outputs/vampire01

img_00000.png img_00009.png img_00018.png img_00027.png img_00036.png
img_00001.png img_00010.png img_00019.png img_00028.png img_00037.png
img_00002.png img_00011.png img_00020.png img_00029.png img_00038.png
img_00003.png img_00012.png img_00021.png img_00030.png img_00039.png
img_00004.png img_00013.png img_00022.png img_00031.png img_00040.png
img_00005.png img_00014.png img_00023.png img_00032.png img_00041.png
img_00006.png img_00015.png img_00024.png img_00033.png img_00042.png
img_00007.png img_00016.png img_00025.png img_00034.png img_00043.png
img_00008.png img_00017.png img_00026.png img_00035.png img_00044.png

abs_path='/opt/homebrew/bin/'
max_frames=1000
fps = 12
image_path = "outputs/vampire01/img_%05d.png"   #note: this includes a regular expression to define the sequencing as xxxxx (5 digits).
mp4_path = "video/vampire.mp4"

cmd = [
    abs_path+'ffmpeg',
    '-y',
    '-vcodec', 'png',
    '-r', str(fps),
    '-start_number', str(0),
    '-i', image_path,
    '-frames:v', str(max_frames),
    '-c:v', 'libx264',
    '-vf',
    f'fps={fps}',
    '-pix_fmt', 'yuv420p',
    '-crf', '17',
    '-preset', 'veryfast',
    '-pattern_type', 'sequence',
    mp4_path
    ]

print(' '.join(cmd))

/opt/homebrew/bin/ffmpeg -y -vcodec png -r 12 -start_number 0 -i outputs/vampire01/img_%05d.png -frames:v 1000 -c:v libx264 -vf fps=12 -pix_fmt yuv420p -crf 17 -preset veryfast -pattern_type sequence video/vampire.mp4

We could run the command above in our Mac OS terminal shell.

Note: we have used the absolute path to run the ffmpeg executable to avoid ffmpeg not found errors. This isn’t required if running the ffmpeg from a shell.

ffmpeg parameters explained

Let’s check the ffmpeg command line we’re about to run on the OS. ffmpeg parameters used

• -y Overwrite output files without asking

• -vcodec ‘png’

• -r str(fps) Frame rate

• -start_number 0 Start at sequence number 0

• -i image_path input which will include a squencer with a regular expression

• -frames:v Stops writing frames after set value

• -c:v, libx264’ encodes all video streams with libx264

• -vf Create the filtergraph specified by filtergraph and use it to filter the stream.

• fps Not sure … as we have -r will come back to this

• -pix_fmt, yuv420p pixel format

• -crf 17 Not sure ??? will come back to this

• -preset veryfast

• -pattern_type sequence

• mp4_path The name of the output movie file to create

Click here for more documentation on ffmpeg

import subprocess

process = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
stdout, stderr = process.communicate()
if process.returncode != 0:
    print(stderr)
    raise RuntimeError(stderr)
else:
    print('Video '+mp4_path+' rendered')

Video video/vampire.mp4 rendered

(Source images not upscaled)