[FFmpeg-user] MP4s (and M4As) for music

[Mark Filipak]

ffmpeg^
  -i "c:\chapters.txt"^
  -i c:\01.WAV^
  -i c:\02.WAV^
  -i c:\03.WAV^
  -i c:\04.WAV^
  -i c:\05.WAV^
  -i c:\06.WAV^
  -i c:\07.WAV^
  -i c:\08.WAV^
  -filter_complex "[1:0][2:0][3:0][4:0][5:0][6:0][7:0][8:0]concat=n=8:v=0:a=1[out]"^
  -map_metadata 0 -map "[out]"^
  -c aac -b:a 657.6k^
  "c:\Ashra, Belle Alliance [1980].m4a"


*****
The script above provoked this: "Too many bits 15269.442177 > 12288 per frame requested, clamping to 
max". Of course, I have no idea what that's about. Do you? "Too many bits"?
*****

How did FFmpeg (or AAC) compute "15269.442177 > 12288". What are those numbers? Why does the 
complaint say "bits ... per frame requested" when there's _no_video_, _no_frames_?