How to read MKV bytes as video?

I am receiving fragment of MKV video in bytes. I need to take 1st frame of it for later processing without saving video in disk. For similar problem with image I use OpenCV or PIL and everything works fine, however, I am not able to do the same with video data. Any tips how to read video from bytes to memory object that I could use for later processing with OpenCV or some other library?

Answer

As I don’t have your bytes buffer, I just created an MKV video file with ffmpeg like this:

ffmpeg -i SomeVideo.avi -f matroska -vcodec libx264 video.mkv

I then installed imageio with:

pip install imageio

Then I loaded the entire MKV video into memory so I have something that must look pretty much the same as the bytes object you receive stored in my variable content:

import imageio

# Get bytes of MKV video
with open('video.mkv', 'rb') as file: 
    content = file.read()

Now I should be set up and looking the same as you. Just for reference, the first few bytes of content look like this:

b'x1aExdfxa3x01x00x00x00x00x00x00#Bx86x81x01Bxf7x81x01'

So, let’s continue.

# Wrap the content in a BytesIO and get an ffmpeg reader to read it 
vid = imageio.get_reader(BytesIO(content),  'ffmpeg')

I can now print the mean of each frame like this:

for num, image in enumerate(vid.iter_data()): 
    print(image.mean())

Or get the metadata and print it like this:

metadata = vid.get_meta_data()                                                             

print(metadata)

{'plugin': 'ffmpeg',
 'nframes': 750,
 'ffmpeg_version': '4.1 built with Apple LLVM version 10.0.0 (clang-1000.11.45.5)',
 'fps': 25.0,
 'source_size': (1280, 720),
 'size': (1280, 720),
 'duration': 30.0}

Keywords: Python, video, frame, individual frame, FFmpeg, imageio, single frame, BytesIO, bytes, MKV, Matroska.