In the RESUME project (Reconfigurable Embedded Systems for Use in Multimedia Environments) we explore the benefits of an implementation of scalable multimedia applications using reconfigurable hardware by building an FPGA implementation of a scalable wavelet-based video decoder. The term "scalable" refers to a design that can easily accommodate changes in quality of service with minimal computational overhead. This is important for portable devices that have different Quality of Service (QoS) requirements and have varying power restrictions.
The scalable video decoder consists of three major blocks: a Wavelet Entropy Decoder (WED), an Inverse Discrete Wavelet Transformer (IDWT) and a Motion Compensator (MC). The WED decodes entropy encoded parts of the video stream into wavelet transformed frames. These frames are decoded bitlayer per bitlayer. The more bitlayers are decoded the higher the image quality (scalability in image quality). Resolution scalability is obtained as an inherent property of the IDWT. Finally framerate scalability is achieved through hierarchical motion compensation.
In this article we present the results of our investigation into the hardware implementation of such a scalable video codec. In particular we found that the implementation of the entropy codec is a significant bottleneck. We present an alternative, hardware-friendly algorithm for entropy coding with excellent data locality (both temporal and spatial), streaming capabilities, a high degree of parallelism, a smaller memory footprint and state-of-the-art compression while maintaining all required scalability properties. These claims are supported by an effective hardware implementation on an FPGA.
Computer networks and the internet have taken an important role in modern society. Together with their development, the need for digital video transmission over these networks has grown. To cope with the user demands and limitations of the network, compression of the video material has become an important issue. Additionally, many video-applications require flexibility in terms of scalability and complexity (e.g. HD/SD-TV, video-surveillance). Current ITU-T and ISO/IEC video compression standards (MPEG-x, H.26-x) lack efficient support for these types of scalability. Wavelet-based compression techniques have been proposed to tackle this problem, of which the Motion Compensated Temporal Filtering (MCTF)-based architectures couple state-of-the-art performance with full (quality, resolution, and frame-rate) scalability. However, a significant drawback of these architectures is their high complexity. The computational and memory complexity of both spatial domain (SD) MCTF and in-band (IB) MCTF video codec instantiations are examined in this study. Comparisons in terms of complexity versus performance are presented for both types of codecs. The paper indicates how complexity scalability can be achieved in such video-codecs, and analyses some of the trade-offs between complexity and coding performance. Finally, guidelines on how to implement a fully scalable video-codec that incorporates quality, temporal, resolution and complexity scalability are proposed.