Transcoding Architectures There are different standard transcoding architectures for changing bit rate, spatial resolution, format conversion. Few of them are discussed here in sections to follow: Open Loop Transcoding Architecture Figure 4-1 shows and open-loop system. In the open-loop system, the bit stream is variable-length decoded (VLD) to extract the variable-length code words corresponding to the quantized DCT coefficients, as well as MB data corresponding to the motion vectors and other MB-level information. In this scheme, the quantized coefficients are inverse quantized and then simply requantized to satisfy the new output bit rate. Finally, the requantized coefficients and stored MB-level information are variable length coded (VLC). Regardless of the techniques used to achieve the reduced rate, open-loop systems are relatively simple a frame memory is not required and there is no need for an IDCT. In terms of quality, better coding efficiency can be obtained by the requantization approach since the variable-length codes that are used for the requantized data will be more efficient. However, open-loop architectures are subject to drift[16]. Figure Open Loop, partial decoding to DCT coefficients —: then requantize [16]
Transcoding Architectures There are different standard transcoding architectures for changing bit rate, spatial resolution, format conversion. Few of them are discussed here in sections to follow: Open Loop Transcoding Architecture Figure 4-1 shows and open-loop system. In the open-loop system, the bit stream is variable-length decoded (VLD) to extract the variable-length code words corresponding to the quantized DCT coefficients, as well as MB data corresponding to the motion vectors and other MB-level information. In this scheme, the quantized coefficients are inverse quantized and then simply requantized to satisfy the new output bit rate. Finally, the requantized coefficients and stored MB-level information are variable length coded (VLC). Regardless of the techniques used to achieve the reduced rate, open-loop systems are relatively simple a frame memory is not required and there is no need for an IDCT. In terms of quality, better coding efficiency can be obtained by the requantization approach since the variable-length codes that are used for the requantized data will be more efficient. However, open-loop architectures are subject to drift[16]. Figure —: Open Loop, partial decoding to DCT coefficients then requantize [16]