Intra Block Copy for Screen Content in the Emerging AV1 Video Codec

Screen content coding plays an important role in many applications. To meet the growing demands of screen content coding, the emerging AV1 video codec incorporates several coding tools, which are specially designed for screen content utilizing its distinctive characteristics. Among these tools, the intra block copy utilizes the characteristic that repeating patterns frequently occur in screen content. This paper presents the technology of intra block copy in AV1. In particular, to efficiently search the predictor in the reconstructed regions of the current picture, AV1 uses the hash matching method at the encoder side. For the generation of hash table, a bottom-to-up manner is adopted to reduce the redundant computation and then decrease the encoding time. In addition, several constraints are involved to facilitate hardware design. Experimental results demonstrate that the intra block copy in AV1 can bring 27.1% bitrate saving for screen content. When compared with the non hash-based intra block copy, the hash-based method achieves 12.2% bitrate saving.