Real-time multi-pass MPEG video coding for video-on-demand over ADSL

Abstract

There have been increasing market demands to develop more effective schemes for applying MPEG video coding standard to meet the challenges from the emerging applications. We present a real-time multi-pass MPEG video coding system for constant bit rate (CBR) applications, such as Video-on-Demand (VoD) over ADSL. This scheme employs two MPEG encoders. Both encoders operate at the same CBR. The second encoder has a buffer to delay the input by an amount of time relative to the first encoder to create a look-ahead window. In encoding, the first encoder collects statistical and rate-quality characteristic information. An on-line processor then uses the collected information to derive the best coding strategy for the second encoder to encode the incoming frames in the look-ahead window. The second encoder uses the encoding parameters from the processor as the coding guide to execute the coding strategy and produce the compressed bitstream. Results on an IBM MPEG-2 encoder testing system with a 15 frame look-ahead window have shown that the scheme can obtain 0.6 to 1.6dB improvement in PSNR over the conventional single encoder on MPEG test video sources. Moreover, measured by the Tektronix Inc.'s Picture Quality Analysis (PQA) System, this scheme achieved 0.87 ∼ 1.35 reduction in PQA index. The visual quality improvement is also very evident.