dm8148 rdk2.8 encode camlink 2 stream failed

i use dm8148 with rdk 2.8  to encode 2 camlink streams,vin0 with 1024x768,vin1 with 320x256, but i failed to encode 2 streams,only have one . when i only connect one,it worked well.my link line is capture---->nfs--->out vpss--->in video--->enc--->out video---->in a8---->net. then I found it make a mistake at video encode part. in file--"encLink_common.c" ,function "EncLink_codecSubmitData()",line "status = Utils_bitbufGetEmptyBuf(&pObj->outObj.bufOutQue...".this function can not get the buf.When i add a scaler link after nfs link to make 320x256 to 1024x768 ,with the same resoultion,vide m3 can encode  2 streams.Then i test scale 2 resoultion to the same resolution, it works well.A8 can get double bitstreams.So i want someone to help me to solve this problem.   Thank you very much.