# Video Error-Resilience Research Based on Error-Resilient Screen Content
## 2 Related Work  
In the video error recovery technology, fault-tolerant coding belongs to the forward technology. The forward technology refers to introducing redundant error correction bits to the transmission stream at the encoding end. Under certain conditions, the transmission error can be automatically corrected in the decoding process, and the BER (bit error rate) of the received stream can be reduced. According to the standard coding scheme, fault-tolerant video code stream is generated to solve the error problem in the video transmission process. Through the change of coding mode, the impact of error on the decoded video quality is suppressed as much as possible [14]. Error concealment, as a post-processing technology, repairs and conceals the data in lossy transmission according to the normal received stream information, so that the decoded video can be as close as possible to the original encoded image [15]. In the feedback-based coding transmission framework, when the receiver finds data loss, it can choose the coding unit correctly received in the reference image sequence to realize error recovery. For the coding transmission system without feedback, the redundant slice coding method can add one or several redundant representations of a coding unit in the code stream [16]. As the decoder decodes the received stream, the ordinary information is first utilized. If the received stream is lost, the added redundant slice is considered to decode and reconstruct.  
When the transmission error occurs in the main frame, the redundant frame is decoded so that the decoder can obtain acceptable video quality compared with the original video. In the process of video transmission, redundancy coding can be realized in video source coding and channel coding, respectively. The additional redundant content can be either the redundant image encoded for the whole image, or the redundant slice encoded for a specific region or some macroblocks [17].  
In the coding process, redundant frames often use different coding parameters from the main frame to improve the rate-distortion performance. [PERSON] et al. [18] propose a redundant image coding method based on reference frame selection with motion vector and error diffusion distortion to determine whether the current frame encodes redundant frames, where reference frame selection is just utilized in redundant frames. The probability of using redundant frames is only 1-p, where p denotes the probability of independent packet losses for image frames. As a result, the loss reduction with reference frame selection mechanism in redundant frames may not offset the increase of rate-distortion cost caused by the increase of code rate.  
Redundant slice embedding is equivalent to the repeated encoding of pictures, which consumes more encoding bits [19]. Therefore, it is preferable to add redundancy to important areas rather than to protect all areas. For error-resilient coding with redundant frames, redundant frames are encoded to improve the robustness of I-frames, so as to further enhance the image transmission quality of video [9]. The method based on adjusting the coding parameters of the redundant frame and main frame does not consider the influence of different scene features. The adaptive redundant frame coding algorithm only uses a fixed reference frame selection mode for redundant frames and does not use other error-resilient methods for main frames, which makes the generation mechanisms of redundant images (redundant slices) simple and limits its adaptability to different network conditions and video scenes.