Linelet, an Ultra-Low Complexity, Ultra-Low Latency Video Codec for Adaptation of HD-SDI to Ethernet
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In this project we have designed, specified, implemented, optimized and evaluated a new ultra-low latency (< 1 ms) and ultra-low complexity intra-only video compression codec, Linelet, which is able to compress 1080p50 and beyond in real-time on regular desktop PC equipment. There are strong indications that 4K@60 encoding is possible in real-time on powerful desktop equipment. The broadcasting industry today is moving towards 4K and ultra-high definition resolutions and this puts greater burdens on transmission equipment which need to transmit the highest quality video material during production in real-time. We therefore see the need for a lightweight compression solution which can keep the bandwidth down while keeping the pristine quality needed for production. Such a solution must be cheap, fast and have near-zero latency in order to justify the cost of adding compression.With a lightweight compression scheme we enable the possibility to transmit production video over Ethernet links. We can compress 1.5 Gbit/s and 3.0 Gbit/s HD video into a 1 gigabit ethernet link, or 12 Gbit/s 4K video down to a 10 gigabit ethernet link. Linelet is based on the discrete wavelet transform and uses the 5/3 wavelet filter for simplicityand reversibility of all operations. Linelets focus is transforming video data horizontally for near-zero latency, but also allows for a simple method to exploit vertical redundancies. Exploiting vertical redundancies lead to a 3 dB improvement in PSNR and vastly improved visual quality over a design which only considers horizontal redundancy. Linelets target use case is to be implemented in either an FPGA or ASIC, working with uncompressed video signals in real-time. The codec is designed ground-up for simplicity, requires little memory and avoids any expensive arithmetic. Entropy coding is vastly simplified over conventional approaches which ensures very high encoder throughput (5 Gbit/s and beyond) even on desktop PC hardware. Using our software implementation of Linelet, we performed a small-scale subjective evaluation with experts in the field based on recommendations in ITU-R BT.500 and the evaluation indicates that Linelet remains visually lossless at 1:2, 1:4 and even 1:6 compression rates for very difficult test sequences such as ParkJoy and Horse at a viewing distance of 3H. The experts were very familiar with these sequences. Further tests should be carried out to verify this.