add background music for last 5 second or fade in last 5 seconds a mp4 video

Question

I want to add background music for last 5 second in a mp4 video.how ? or fade in last 5 seconds. first time fade out then fade in for last 5 seconds.Please help. I tried

ffmpeg -y -r 30 -i a.mp4 -i nn.mp3 -filter_complex "[0:a]volume=0,asplit[0a][0acf];
[1:a]adelay=15s|15s[1a]; 
[0a][1a]amix=inputs=2:duration=first:dropout_transition=0,volume=2,afifo[outro];
[0acf]atrim=0:16,afifo[0acf];
[outro][0acf]acrossfade=d=20[outro]; 
[0:a][outro]amix=duration=first:weights=\'2 1\'[a]" -map 0:v -c:v copy -map [a] output.mp4 

Answer 1

Sorry for unclear question. But after trying a day i got the solution for the question.

The code is -

ffmpeg -y -r 30 -i a.mp4 -i a.mp3 -c:v copy  -filter_complex "[0:a]aformat=fltp:44100:stereo,apad[0a];[1]volume=enable=\'between(t,0,20)\':volume=.01:eval=frame[1a];[0a][1a]amerge[a]" -map 0:v -map "[a]" -ac 2