H.264, also known as AVC (Advanced Video Coding), is a video compression standard that has gained significant popularity due to its efficiency, flexibility, and wide range of applications. It’s one of the most commonly used video codecs today. Here’s an overview of H.264:
Design Purpose: H.264 was developed to provide good video quality at significantly lower bit rates than previous standards like H.263. It was intended for a wide range of applications from low bit-rate Internet streaming to high-definition broadcast and Digital Cinema.
Profiles and Levels: H.264 defines various profiles, which are subsets of the standard catering to specific classes of applications. These profiles define which features can be used. Additionally, levels define maximum values for certain parameters (like resolution or frame rate) within those profiles.
Compression Techniques:
- Intra Prediction: For spatial compression, H.264 introduced a method called intra prediction, where parts of the same frame predict other parts.
- Inter Prediction: For temporal compression, it uses motion compensation with multiple reference frames.
- Transform and Quantization: H.264 uses a 4×4 or 8×8 (depending on settings) DCT-like transform for frequency transformation.
- Entropy Coding: The standard uses two entropy coding methods: CAVLC (Context Adaptive Variable Length Coding) and CABAC (Context Adaptive Binary Arithmetic Coding), with CABAC providing better compression but being more computationally intensive.
Network Friendliness: H.264 was designed with packet-switched networks in mind. It has features like slice structures that allow better error resilience and recovery from data loss.
Annexes: Like H.263, H.264 has several annexes to introduce optional features, such as SVC (Scalable Video Coding) for scalability in resolution and bit rate.
Applications: H.264 is used in a myriad of applications:
- Streaming services (e.g., YouTube, Netflix)
- Video conferencing tools (e.g., Zoom, Skype)
- Broadcast television
- Blu-ray discs
- Surveillance cameras
- And many others.
Licensing: H.264 is patented, and its commercial use requires paying royalties. However, this hasn’t significantly hindered its widespread adoption.
Evolution: Following H.264, the ITU-T and ISO/IEC developed H.265 or HEVC (High Efficiency Video Coding), which aims to provide similar video quality at half the bit rate of H.264.
In summary, H.264 represents a significant milestone in video codec technology, balancing compression efficiency, video quality, and computational complexity. Its adoption across various platforms and applications underscores its versatility and effectiveness.