return value of opus_dred_parse

[walletiger]

for encoder i set OPUS_SET_DRED_DURATION to 100,
while decoding stream , i set dred_input with loss frames , but the return value of opus_dred_parse sometimes smaller than dred_input , sometimes larger !!!
i dont no why ?
how can i deal with the return value smaller than input ?

/* Only decode the amount we need to fill in the gap. */
ret = opus_dred_parse(dred_dec, dred, data, len, IMIN(48000, IMAX(0, dred_input)), sampling_rate, &dred_end, 0);
printf("--------dred_input=%d, opus_dred_parse ret = %d\n", dred_input, ret);

log print:
--------dred_input=960, opus_dred_parse ret = 720
--------dred_input=960, opus_dred_parse ret = 720
--------dred_input=960, opus_dred_parse ret = 720
--------dred_input=960, opus_dred_parse ret = 720
--------dred_input=4800, opus_dred_parse ret = 4560
--------dred_input=960, opus_dred_parse ret = 720
--------dred_input=1920, opus_dred_parse ret = 2640