1. A tangible non-transitory computer-readable medium comprising instructions that when executed by one or more processors cause the one or more processors to: decode a sequence of predicted and bidirectional predicted frames in a bitstream, each frame comprising pixel values, wherein at least one region within a bidirectional predicted frame is determined using pixel values from at least a first referenceable frame and a second referenceable frame, the first referenceable frame being prior to the second referenceable frame in decoding order and subsequent to the second referenceable frame in display order, wherein the bidirectional predicted frame is prior to both the first and the second referenceable frames in display order, and wherein the bitstream comprises an expiration signal that identifies the first referenceable frame as expired, and in response to the expiration signal, the one or more processors discard the first referenceable frame as a candidate referenceable frame in decoding the bitstream.