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Save Bandwidth with Capped CRF

Video engineers are constantly seeking ways to deliver high-quality video more efficiently and cost-effectively. Among the innovative techniques gaining traction is capped Constant Rate Factor (CRF) encoding, a form of Content-Adaptive Encoding (CAE), which NETINT recently introduced across our Video Processing Unit (VPU) product lines for x264 and x265. In this blog, we explore why capped CRF is essential for engineers seeking to streamline video delivery and save on bandwidth costs.

Capped CRF - The Efficient Encoding Solution

Capped CRF is a smart bitrate control technique that combines the benefits of CRF encoding with a bit rate cap. Unlike Variable Bitrate Encoding (VBR) and Constant Bitrate Encoding (CBR), which target specific bitrates, capped CRF targets a specific quality level controlled by the CRF value, with a bitrate cap applied if the encoder can’t meet the quality level below the bitrate cap.

A typical capped CRF command string might look like this:

crf 21    -maxrate 6MB

This tells the encoder to encode to CRF 21 quality, but don’t exceed 6 Mbps. Let’s see how this might work with the football video shown in the figure, which compares capped CRF at these parameters with a CBR file encoded to 6 Mbps.

NETINT - Bitrate Comparison - Capped CRF

With the x264 codec, CRF 21 typically delivers a VMAF score of around 95. With easy-to-encode sideline shots, the CRF value would control the encoding, delivering 95 VMAF quality at 2 Mbps, a substantial savings over CBR at 6 Mbps.

During actual plays, the 6 Mbps bitrate cap would control, delivering the same quality as CBR at 6 Mbps. So, capped CRF saves bandwidth with easy-to-encode scenes while delivering equivalent to CBR quality with hard-to-encode scenes.

Ease of Integration

As implemented within the NETINT product line, capped CRF requires no additional technology licensing or complex integration – you simply upgrade your products and change your encoding command string. This means that you can seamlessly implement the feature across NETINT’s VPUs without extensive adjustments or additional investments.

NETINT’s capped CRF is compatible with H.264 and HEVC, and AV1 coming (Quadra only), so you can use the feature across different codec options to suit your specific project requirements. Regardless of the codec used, capped CRF delivers consistent video quality with the potential for bandwidth savings, making it a valuable tool for optimizing video delivery.

A Game Changer

By deploying capped CRF, engineers can efficiently deliver high-quality video streams, enhance viewer experiences, and reduce operational expenses. As the demand for video streaming continues to grow, Capped CRF emerges as a game-changer for engineers striving to stay at the forefront of video delivery optimization.

You can read more about how capped CRF works here. You can read more about Quadra VPUs here, and T408 transcoders here.

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