A Method to Improve Perceptual Quality of Intra- Refresh-Enabled Low-Latency Video Coding

A typical video encoder includes into the generated bit stream Instantaneous Decoder Refresh (IDR) units. This allows random access playback at the receiver side as well as graceful recovery from potential channel errors. Such forced IDR units typically come in repetitive patterns, which may negatively impact the perceived subjective quality if not handled properly. The reason is that the restricted encoding process of an IDR unit results in a different (regardless higher or lower) quality of reconstructed signal compared to the surrounding non-IDR ones. This causes eye-capturing irritating periodical artifacts when it occurs in patterns. This phenomenon gets to be even more pronounced when the intra refresh feature is enabled, since it forces IDR and nonIDR units to co-exist within the same picture, making the quality difference more noticeable. This paper proposes a method to hide such undesired patterns that naturally accompany the intra refresh feature. Two ideas are presented; the first one imposes restrictions that prevent unwanted fluctuations in the quantization levels between different regions of the picture, while the second hides the repetitive pattern by randomly forcing IDR blocks within specific regions of the refreshed picture. Results show that the proposed method results in improvements in subjective quality.