How to archive PNG sequences?


#1

I make a lot of animations in Cinema 4D, and I usually render those animations out as PNG sequences to then be used in After Effects. Since the renders take a while, I usually keep these PNG sequences even after the project is finished in case I need to come back to it.

Naturally, these PNG files can take up a lot of space. I’ve been looking into lossless video codecs to compress them, and have had some success (in other words, the lossless .mp4 file I get is much smaller than all the original PNG files themselves) with ffmpeg’s libx264rgb, but only for 24-bit RGB images. In other words, when I have animations with alpha channels, or the times when I export 8-bit depth channels, that codec doesn’t suffice (libx264 doesn’t support alpha and the .mp4 file created from the 8-bit png files is usually bigger than original PNG files themselves).

How do you store your PNG sequences for archival purposes, specifically 8-bit PNGs or those with alpha channels? Saving space on disk is my primary concern, and storing them losslessly is ideal.


#2

Unless I’ve missed a memo,. mp4 isnt lossless, no matter what bitrate.

Maybe the easiest answer is just get a bigger drive? 16TB drives are commonly available with 18 and 20TB just around the corner.


#3

As @3DFluff said, I just get more storage space. It’s worth it for me to keep the original renders intact. However, if I’m really in a situation and need more space immediately, I’ll re-render the png or tif sequence to ProRes4444 which is a lossless industry standard codec that supports alpha. Mac-centric of course.


#4

.mp4 is just the container. The libx264 codec does have a lossless mode. For example:
ffmpeg -i png_files%04d.png -c:v libx264 -qp 0 -preset veryslow out.mp4
I’ve managed to save many gigabytes with libx264 since it’s inter-frame. I haven’t given consideration to ProRes4444 though; I’ll try that next and compare.


#5

Prores4444 isn’t lossless either. The alpha channels are but the RGB component does get lossy compression. Not enough that it matters, but it is there.

You’re right about h264, they can indeed be lossless, never actually encountered one though.

Regarding alphas, in theory hevc/h265 supports alpha channels, as would webm, but they’re currently very poorly supported formats so finding something to encode them with a useful workflow is an issue. Personally Im a fan of exr with dwaa encoding. They support all the channels you need and are virtually lossless under most sensible working conditions.


#6

Just 7zip them. I used to render in AVI and keep them compressed for future compositions or better video encodings.