lossless frame extraction from video

Question

I have an mp4 video file with these characteristics:

-Encoder: Lavf58.29.100

I want to extract each frame as an image, with the following requirements:

• one image file is one frame (i.e., account for variable framerates to work in all cases),

• the image file has to be lossless TIFF.

I use Linux and would prefer Python to do this, but I can also use FFmpeg.

However, I have seen some other posts here, but they are either not-replied to or just need JPG format. I have read the imwrite documentation (OpenCV) and saw that it is actually possible to export as TIFF (even with different bit-depths), but I can't see an example of using that. I also do not know how to confirm if the exported TIFF is actually without compression.

The reason I need each frame as a lossless image file is that I need the images for further analysis in research, and I don't want to lose any information at this stage (the sequence of images is the starting 'raw material' of my analysis pipeline).

Answer 1

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After research and help from here and other places, I found 3 ways to do it.

Pillow (Python)

• Command: img.save(output_filename,format='TIFF',compression='tiff_deflate',tiffinfo={})
  
• Result: Generates 2246 TIFF files (variable sizes, between 761 and 566 KiB)

OpenCV (Python)

• Command: cv2.imwrite(name, frame, [cv2.IMWRITE_TIFF_COMPRESSION, 1])
  
• Result: Generates 2246 TIFF files (6.4 MiB each one)

ffmpeg (tested on Linux)

• Command: (see different ways)
  
• Result: Generates 2246 or 2247 TIFF files, depending on the exact command (see different ways). Each file is 2.8 MiB
  

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Edit 1: The differences between file sizes in each option (e.g. 600 KiB vs 6.4 MiB vs 2.8 MiB) seem to be related to the compression used by different algorithms. I used exiftool and found that in deed the compression is different: uncompressed (Python/OpenCV), PackBits (ffmpeg) and Adobe Deflate (Python/Pillow).

Edit 2: after further inspection and comparison, I observed that Python/Pillow (which uses Adobe Deflate method) also significantly changed the colors in the picture! I am unsure if this is due to the compression method or is something else done by Pillow.

Answer 2

This ffmpeg command should do the trick for you:

ffmpeg -i in.mp4 -vf "select=eq(n\,0),setpts=N/(FRAME_RATE*TB)" output_%08d.tif

Note: Your input is allready encoded in a lossy encoding, so you will have artifacts from the h264 codec.