CODEWITHSUNDEEP
c++arraysvideocolorsmemory-efficient
Fly
Fly

Reputation: 862

Most efficient way to store video data

In order to accomplish some specific editing on some .avi files, I'd like to create an application (in C++) that is able to load, edit, and save those .avi files. But, what is the most efficient way? When first thinking about it, a simple 3D-Array containing a 2D-array of pixels for every frame seems the simplest solution; But then its size would be ENORMOUS. I mean, let's assume that a pixel only needs a color. One color would mean 3bytes (1char r, 1char b, 1char g). If I now have a 1920x1080 video format, this would mean 2MEGABYTES for only one frame! This data may or may not be smaller if using pointers for the colors, so that alreay used colors wont take more size - I don't really know, since I'm pretty new to C++ and the whole low-level stuff. (As a comparison: One of my AVI files recorded with Xvid codec is 40seconds long, 30fps, and only has 2MB.) So how would you actually store the video data (Not even the audio, just the video) efficiently (while still being easily able to perform per-frame-changes on it)?

Upvotes: 0

Views: 1613

Answers (1)

rghome
rghome

Reputation: 8841

As you have realised, uncompressed video is enormous and it is not practical to store an entire video in this way.

Video compression is an extremely complex topic, but more-or-less, it works as follows: certain "key-frames" are compressed using fairly standard compression techniques similar or identical to still-photo compression such as JPEG. Frames following key-frames are compressed by comparing the frame with the previous one and looking for changes (such as moving blocks). Every now and again, a new key-frame is used.

You don't really have to worry much about that as you are not going to write your own video coder/decoder (codec). There are standard ones.

What will happen is that your program will decode the compressed video frame-by-frame and keep a certain number of frames in memory while you are working on them and then re-encode them when it is finished. In the uncompressed form, you will have access to the individual pixels and can work on them how you want.

You are probably not going to do that either by yourself - it is very hard. You probably need to use a framework, such as OpenCV. There are a huge number of standard filters and tools built in to these frameworks, and it may be that what you want to do is already implemented somewhere.

The OpenCV framework can return individual frames in a Mat object and you can then access the pixels. See this post Get Pixels from Mat

OpenCV

Tutorial page: Open CV Tutorial

Upvotes: 2

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