Encoder buffer constraints for video transmission over networks with no quality-of-service guarantees
Real-time transmission of video over networks with no QoS guarantees (e.g., the Internet) is increasingly becoming an important application area in multimedia communications. One of the key challenges in this area is maintaining continuous decoding and playback at the receiver despite severe network impairments such as high packet-loss-ratios, packet-delay-variations, and unbounded roundtrip delays. A popular solution to this problem is to introduce large buffering delays at the receiver to (partially) compensate for the network impairments. This solution, however, is not a viable option for clients with limited resources and for applications requiring minimal delays. We advocate a new approach to this challenge. We derive a new set of encoder buffer constraints taking into consideration network impairments. We show how these new constraints can significantly reduce (or possibly eliminate) underflow and overflow events at the decoder while enabling the receiver to maintain its ideal decoder buffer size and buffering-delay requirements (needed for video transmission under ideal conditions). We present the results of more than 40 hours of video transmission over the (real) Internet. These results demonstrate the advantages and limitations (asymptotic behavior) of our proposed encoder-buffer constraints.