In real-time video communication, retransmitting lost packets over high-latency networks is not viable due to strict latency requirements. To counter packet losses without retransmission, two primary strategies are employed -- encoder-based forward error correction (FEC) and decoder-based error concealment. The former encodes data with redundancy before transmission, yet determining the optimal redundancy level in advance proves challenging. The latter reconstructs video from partially received frames, but dividing a frame into independently coded partitions inherently compromises compression efficiency, and the lost information cannot be effectively recovered by the decoder without adapting the encoder. We present a loss-resilient real-time video system called GRACE, which preserves the user's quality of experience (QoE) across a wide range of packet losses through a new neural video codec. Central to GRACE's enhanced loss resilience is its joint training of the neural encoder and decoder under a spectrum of simulated packet losses. In lossless scenarios, GRACE achieves video quality on par with conventional codecs (e.g., H.265). As the loss rate escalates, GRACE exhibits a more graceful, less pronounced decline in quality, consistently outperforming other loss-resilient schemes. Through extensive evaluation on various videos and real network traces, we demonstrate that GRACE reduces undecodable frames by 95% and stall duration by 90% compared with FEC, while markedly boosting video quality over error concealment methods. In a user study with 240 crowdsourced participants and 960 subjective ratings, GRACE registers a 38% higher mean opinion score (MOS) than other baselines.

翻译：在实时视频通信中，由于严格的延迟约束，高延迟网络环境下重传丢失数据包并不可行。为在无重传条件下应对数据包丢失，主要采用两种策略——基于编码器的前向纠错（FEC）与基于解码器的错误隐藏。前者在传输前通过冗余编码数据，但预先确定最优冗余级别极具挑战性；后者从部分接收帧中重建视频，但将帧划分为独立编码分块本质上会降低压缩效率，且不调整编码器时，解码器无法有效恢复丢失信息。我们提出一种名为GRACE的抗丢包实时视频系统，通过新型神经视频编解码器在广泛数据包丢失条件下保持用户体验质量（QoE）。GRACE增强抗丢包能力的核心在于：在模拟多种丢包场景下对神经编码器与解码器进行联合训练。在无丢包场景下，GRACE的视频质量与传统编解码器（如H.265）相当。随着丢包率上升，GRACE呈现更平滑、更轻微的质量下降，始终优于其他抗丢包方案。通过在不同视频片段与真实网络轨迹上的全面评估，我们证明：与FEC相比，GRACE将不可解码帧减少95%，卡顿时长减少90%；与错误隐藏方法相比，其视频质量显著提升。在包含240名众包参与者与960份主观评分的用户研究中，GRACE的MOS（平均意见得分）较其他基线方案高出38%。