only join video & audio, not convert

[vitalitasia]

is there a way to prevent vividl from converting the whole video and just making it join video and audio, cause if i join audio and video manually in avidemux its very fast, while vividl seems to convert the whole video and audio from what it seems when i look the cpu usage and time to finish. apprecitate any help. if its a format issue, please mention which formats allow a merge of mp4 video and audio without convert. thank you very much