Video Decoder Concealment

Sammanfattning: H.264 is a new video coding standard developed jointly by ITU – T and the Moving Picture Expert Group (MPEG). It outperforms MPEG-2 by requiring around 50 % of the bit rate for a similar perceptual quality. It allows low bitrate networks to supply video at a quality previously not possible. Much of the previous work on concealment focuses on losses on the block level and uses the surrounding area information which is highly correlated. This thesis on the other hand analyzes and proposes ways to conceal errors in areas affecting much larger areas of a frame and with little information available from neighboring macroblocks. The methods proposed in this thesis include using weighted interpolation to create the visual effect of smoothness for the user when doing spatial concealment. High frequencies are also removed from concealed areas after inter concealment using a spatial filter. A background detector is proposed to reduce background blurriness and a method is proposed to dynamically adjust the range of pixel values after the concealment is done. This thesis work introduces the use of a scene change detector when doing interframe concealment to avoid mixing two different scenes. The results show that the perceived video quality can be significantly improved partly by removing highly noticeable artifacts and partly by giving a smooth image.