We describe a new approach to image sequence coding based upon variable-rate entropy-constrained subband coding (ECSBC) and, furthermore, develop the corresponding practical implementation of this ECSBC scheme for fixed-rate channels by extending previously developed adaptive entropy-coded quantization (AEC) techniques. In particular, a buffer-adaptive arithmetic-coded implementation of the ECSBC scheme, denoted ECSBC/AEC, is described which completely eliminates the generally associated encoder buffer overflow/underflow problems, even with a very small encoder buffer. This scheme utilizes hierarchial motion-compensated prediction in a backward-adaptive interframe coding system. Color image sequences are encoded in the YIQ domain. We demonstrate that this ECSBC/AEC scheme operating on real-world image sequences performs very close to the limiting performance achievable only with an encoder buffer of infinite size. Furthermore, we demonstrate that HDTV-quality image sequences can be encoded at bandwidths consistent with existing broadcast television systems. Finally, we show that this scheme delivers extremely robust performance under source mismatch conditions for both video-conferencing and HDTV video material.