How do video encoders achieve low-latency conversion of HDMI high-definition video to network video streams?
Publish Time: 2025-09-22
Traditional HDMI cable transmission is limited by distance and cabling complexity, making it difficult to meet the needs of cross-regional, multi-terminal video distribution. Converting HDMI high-definition video signals to network video streams using video encoders has become a key technology for achieving long-distance, flexible, and efficient transmission. However, achieving "low latency" while maintaining image quality is a major challenge for users. The answer lies in the coordinated design of video encoder hardware architecture, encoding algorithms, network optimization, and other aspects.
1. High-Speed Signal Acquisition: Compressing Latency at the Source
Low latency starts with signal acquisition. Video encoders use dedicated HDMI receiver chips. This process requires extremely high clock synchronization accuracy and data throughput. High-end video encoders use FPGAs or ASICs to pre-process the raw video data, avoiding the latency fluctuations associated with general-purpose CPU processing. Hardware-level pass-through technology keeps the latency of the video signal before it enters the encoding module to milliseconds, saving valuable time for subsequent processing.
2. High-Efficiency Video Coding: Combining H.265 with Low-Latency Mode
Captured raw video data is enormous. For example, 1080p60 video can reach over 1.5 Gbps, requiring compression encoding for network transmission. Video encoders generally use the H.264 or the more efficient H.265 encoding standard, compressing the bitrate to 10-20 Mbps or even lower while maintaining visual quality. Crucially, video encoders don't pursue extreme compression; instead, they use a "low-latency encoding mode," sacrificing some compression efficiency in exchange for speed. For example, these methods disable B-frames, shorten the GOP length, and employ fast encoding algorithms to reduce encoding latency to under 50ms. Some professional video encoders also support variable bitrates and dynamic bitrate adjustment, optimizing encoding speed in real time based on image complexity.
Software encoding relies on the CPU, making it susceptible to system load and resulting in high latency and instability. Modern video encoders, on the other hand, are often equipped with dedicated video encoding chips that achieve parallel processing through hardware acceleration. These chips feature built-in encoding engines capable of processing multiple video streams simultaneously, while consuming low power and generating minimal heat. Hardware encoding significantly outperforms software solutions, compressing a single frame in 20-40ms, significantly reducing the overall latency of the capture-to-encoding chain.
4. Network Transmission Optimization: Adaptive Bitrate and Protocol Selection
The encoded video stream must be transmitted via a wired network, Wi-Fi, or 4G/5G wireless network. The video encoder has a built-in network module and supports various streaming protocols, including RTMP, RTSP, SRT, and HLS. The SRT protocol is designed for unreliable networks and features forward error correction and a low-latency retransmission mechanism, ensuring smooth transmission even with network fluctuations, keeping latency under 300ms. Furthermore, the video encoder supports adaptive bitrate technology, dynamically adjusting the output bitrate based on network bandwidth to avoid lag. For scenarios requiring ultra-low latency (such as remote control), UDP multicast or proprietary protocols can be used to reduce end-to-end latency to under 200ms.
5. System-Level Optimization: End-to-End Latency Control
True low latency is a system engineering process. The video encoder features extensive firmware optimizations to reduce memory copying, interrupt response, and task scheduling latency. It also supports collaboration with the decoder, optimizing the entire encoding-transmission-decoding chain. For example, enabling "Fast Decoding" mode allows the decoder to begin playback without waiting for a complete GOP, further reducing display latency.
The video encoder achieves low-latency conversion of HDMI HD video to network video streams through the integration of high-speed acquisition, hardware encoding, efficient algorithms, and intelligent network transmission. It serves not only as a signal format converter but also as an acceleration engine for real-time audio and video communication. With the development of 5G and edge computing, the video encoder will continue to evolve towards lower latency, higher image quality, and greater intelligence, providing more reliable technical support for remote video transmission and control.
