An audio encoding device for encoding an audio signal consisting of a plurality of frames, the encoding device comprising: an audio encoding unit for encoding the audio signal; an auxiliary information encoding unit for estimating and encoding auxiliary information about a temporal change of power of the audio signal, the auxiliary information used in packet loss concealment in decoding of the audio signal, wherein the auxiliary information encoding unit estimates and encodes quantized transient power and a flag of sudden change of power, as the auxiliary information about the temporal change of power of the audio signal, wherein the auxiliary information encoding unit is configured to operate in a first mode to encode the quantized transient power and a flag of sudden change of power in response to the flag being indicative of the presence of a transient in the audio signal, and the auxiliary information encoding unit is further configured to operate in a second mode to encode only the flag in response to the flag being indicative of the absence of a transient in the audio signal; and a packet configuration unit configured to generate audio packets, wherein each audio packet consists of a packet header, an audio code of the corresponding frame and the auxiliary information corresponding to a part different than the whole corresponding frame; wherein in a first mode indicative of the presence of a transient in the audio signal, the auxiliary information comprises quantized transient power and a flag of sudden change of power in response to the flag being indicative of the presence of a transient in the audio signal, and, in a second mode indicative of the absence of a transient in the audio signal, the auxiliary information only consists of the flag in response to the flag being indicative of the absence of a transient in the audio signal. an audio encoding unit for encoding the audio signal; an auxiliary information encoding unit for estimating and encoding auxiliary information about a temporal change of power of the audio signal, the auxiliary information used in packet loss concealment in decoding of the audio signal, wherein the auxiliary information encoding unit estimates and encodes quantized transient power and a flag of sudden change of power, as the auxiliary information about the temporal change of power of the audio signal, wherein the auxiliary information encoding unit is configured to operate in a first mode to encode the quantized transient power and a flag of sudden change of power in response to the flag being indicative of the presence of a transient in the audio signal, and the auxiliary information encoding unit is further configured to operate in a second mode to encode only the flag in response to the flag being indicative of the absence of a transient in the audio signal; and a packet configuration unit configured to generate audio packets, wherein each audio packet consists of a packet header, an audio code of the corresponding frame and the auxiliary information corresponding to a part different than the whole corresponding frame; wherein in a first mode indicative of the presence of a transient in the audio signal, the auxiliary information comprises quantized transient power and a flag of sudden change of power in response to the flag being indicative of the presence of a transient in the audio signal, and, in a second mode indicative of the absence of a transient in the audio signal, the auxiliary information only consists of the flag in response to the flag being indicative of the absence of a transient in the audio signal.