Netflix has outlined some of the recent measures taken to improve video quality for subscribers using older devices to connect to the streaming service.
While Netflix is often an earlier adopter of newer codecs, such as AV1, it accepts that not all devices can be upgraded to use the latest decoders owing to issues such as memory limitations and upgrade cycles.
In a blog post the company has detailed how it has previously improved the H.264/AVC Main profile streams by employing per-title optimisations. These have now been up are graded and expected to lower the bitrate streamed by an average of 20% without degrading the picture quality.
Such measures have the effect of reducing footprint on its Content Delivery Network (CDN), Open Connect (OC), the load on ISP networks and the bandwidth usage for subscribers.
Among the work undertaken is a move from objective metrics, such as PSNR, towards VMAF. Netflix says the use of VMAF leads to decisions that favour encodes with higher perceived quality.
Allowing per-chunk bitrate variations instead of using a fixed per-title bitrate, as the original complexity-based encoding scheme has helped the streamer avoid over-allocating bits to less complex content.