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IDR (Instantaneous Decoder Refresh) is a header that the encoder writes to the stream to send a signal to the decoder to reset the references. During the decoding process, some frames (reference frames) are stored in the buffer so that they can be used to restore the following frames. At certain points, the decoder can reset the reference frames and start the decoding process without references. This happens when the IDR is received. This may be necessary in cases where the reference frames have not been reset, but they are no longer needed for further decoding. For example, when the user rewinds the video stream to another timestamp. In this case, the decoder looks for the beginning of the GOP, decodes the i-frame and resets the old reference frames, if IDR is present, and then fills the buffer with new reference frames. It should be noted that the IDR is placed on the I-frame, but not every I-frame must contain an IDR.