Concat two videos with different audio specs

[Merinda]

I want to concatenate a short video with good-quality audio and a short video with poor-quality audio (Avidemux for Windows). I managed to concat two videos but the audio part is now all bad throughout. Is there an easy way to fix the problem? I mean, let the bad part (it's just a home video clip from FB) remain bad and the good part (slide show with a good MP3 track) remain good. The specs are on the attached file. Thanks!You cannot view this attachment.

[eumagga0x2a]

You need to process the poor quality video separately first, with video in copy mode and audio re-encoded as "AAC (lav)" with 128 kbit/s bitrate (I think, this is the default) and "remix to stereo" as audio filter.

The result should be compatible audio track-wise with the good quality video.