I have an .mp4 video file which contains a High Level 3.1 "avc1.64001f" video and a Low-Complexity AAC "mp4a.40.2" audio.
How can I convert the Low-Complexity AAC to "HE-AAC" audiocodec by using the "libfdk_aac" FFmpeg encoder and keep/get the best possible quality? I just want to copy the "avc1.64001f" video into the target file.
Use
ffmpeg -i in.mp4 -c:v copy -c:a libfdk_aac -profile:a aac_he out.mp4
The above will usually default to 48kbps per channel. Add -vbr N for variable bitrate mode where N can be 1-5, with 5 being the best. Or -b:a R e.g. -b:a 128k for constant bitrate mode.