C++ and video compression techniques

04 Oct 2023

Video compression is a crucial aspect of modern multimedia applications. It involves reducing the size of video files while maintaining acceptable visual quality. In this blog post, we will explore some popular video compression techniques and how they are implemented in C++.

Lossless Compression
- Huffman Coding
- Run-Length Encoding
Lossy Compression
- Discrete Cosine Transform (DCT)
- Motion Compensation

1. Lossless Compression

Lossless compression techniques are used when no loss of data is acceptable. These methods aim to eliminate redundant information within a video file without sacrificing quality.

Huffman Coding

Huffman coding is a widely used lossless compression technique. It assigns shorter codes to frequently occurring symbols and longer codes to less frequent symbols. This approach reduces the overall number of bits required to represent the data.

Here’s an example of Huffman coding implementation in C++:

#include <iostream>
#include <queue>
using namespace std;

struct Node {
    char symbol;
    int frequency;
    Node* left;
    Node* right;

    Node(char symbol, int frequency) {
        this->symbol = symbol;
        this->frequency = frequency;
        left = right = nullptr;
    }
};

struct NodeComparator {
    bool operator()(Node* a, Node* b) {
        return a->frequency > b->frequency;
    }
};

void generateHuffmanCodes(Node* root, string code, unordered_map<char, string>& huffmanCodes) {
    if (root == nullptr) {
        return;
    }

    if (root->symbol != '\0') {
        huffmanCodes[root->symbol] = code;
    }

    generateHuffmanCodes(root->left, code + "0", huffmanCodes);
    generateHuffmanCodes(root->right, code + "1", huffmanCodes);
}

unordered_map<char, string> buildHuffmanTree(const vector<char>& symbols, const vector<int>& frequencies) {
    priority_queue<Node*, vector<Node*>, NodeComparator> pq;

    for (int i = 0; i < symbols.size(); i++) {
        Node* node = new Node(symbols[i], frequencies[i]);
        pq.push(node);
    }

    while (pq.size() > 1) {
        Node* left = pq.top();
        pq.pop();
        Node* right = pq.top();
        pq.pop();

        Node* parent = new Node('\0', left->frequency + right->frequency);
        parent->left = left;
        parent->right = right;
        pq.push(parent);
    }

    unordered_map<char, string> huffmanCodes;
    generateHuffmanCodes(pq.top(), "", huffmanCodes);
    return huffmanCodes;
}

int main() {
    vector<char> symbols = {'A', 'B', 'C', 'D', 'E'};
    vector<int> frequencies = {10, 5, 8, 15, 20};

    unordered_map<char, string> huffmanCodes = buildHuffmanTree(symbols, frequencies);

    for (const auto& pair : huffmanCodes) {
        cout << pair.first << ": " << pair.second << endl;
    }

    return 0;
}

Run-Length Encoding

Run-length encoding is a simple lossless compression technique that replaces consecutive repeated symbols with a count and the symbol itself. It is effective when there are long runs of the same symbol in a video frame.

Here’s an example of Run-Length Encoding implementation in C++:

#include <iostream>
using namespace std;

string runLengthEncode(const string& input) {
    string encoded;
    int count = 1;

    for (int i = 1; i <= input.size(); i++) {
        if (i == input.size() || input[i] != input[i - 1]) {
            encoded += to_string(count) + input[i - 1];
            count = 1;
        } else {
            count++;
        }
    }

    return encoded;
}

int main() {
    string input = "AAAABBBCCDAA";
    string encoded = runLengthEncode(input);
    cout << "Encoded: " << encoded << endl;

    return 0;
}

2. Lossy Compression

Lossy compression techniques focus on the removal of non-essential data from video files, sacrificing some quality for higher compression ratios.

Discrete Cosine Transform (DCT)

The Discrete Cosine Transform (DCT) is a widely used lossy compression technique in video coding. It transforms spatial domain data into frequency domain data, allowing for better compression.

Motion Compensation

Motion compensation is a fundamental technique in video coding that exploits the temporal redundancy between consecutive video frames. It involves estimating and compensating for motion between frames to reduce data redundancy.

Conclusion

Video compression techniques play a vital role in reducing the size of video files without significant loss in quality. This blog post discussed some popular compression techniques and provided examples of their implementation in C++. Understanding these concepts is crucial for developers working on multimedia applications or video codecs.

#hashtags: #video #compression

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