The disclosure relates to techniques for video source rate control for video telephony (VT) applications. The source video encoding rate may controlled using a dual-buffer based estimation of a frame budget that defines a number of encoding bits available for a frame of the video. The dual-buffer based estimation technique may track the fullness of a physical video buffer and the fullness of the virtual video buffer. The source video encoding rate is then controlled based on the resulting frame budget. The contents of the virtual buffer depend on constraints imposed by a target encoding rate, while the contents of the physical buffer depend on constraints imposed by varying channel conditions. Consideration of physical video buffer fullness permits the video source rate control technique to be channel-adaptive. Consideration of virtual video buffer fullness permits the video source rate control technique to avoid encoding excessive video that could overwhelm the channel.
