Fade out the main audio track (idea)

HI,

i tried to set an fade in and fade audio out to the main audio track. Without a smooth fadeout and when the audio track is longer then the generated one, the cut is really hard without a fading.

{
outPath: './firevideo.mp4',
audioFilePath: 'assets/audiot1.aac',
keepSourceAudio:true,

...

It seems that there is no such kind of filter yet. I experiment with ffmpeg and was able to set in and out´s without having the excatly duration of the generated clip.

The filtercomplex i used was:
ffmpeg -i firevideo.mp4 -vcodec copy -filter_complex "aevalsrc=0:d=3.6 [a_silence]; [0:a:0] [a_silence] acrossfade=d=3.6" output.mp4

The value 3.6 fades the audio out at the durationtotal-3.6 seconds.

I would like to add this in audio.js in the filter complex section

 async function mixArbitraryAudio({ streams, audioNorm, outputVolume }) {
...

filterComplex += `;${streams.map((s, i) => `[a${i}]`).join('')}amix=inputs=${streams.length}:duration=first:dropout_transition=0:weights=${streams.map((s) => (s.mixVolume != null ? s.mixVolume : 1)).join(' ')}${audioNormArg}${volumeArg}`;

When i insert the ffmpeg synthax i got that the filter can´t implement so many audio tracks. Currently a hot fix is to add this in the index.ts when everything is ready to copy the videotrack and re-encode the main audiotrack.

Is there a way to implement it in the audio.js part?

Start in audio.js at mixArbitraryAudio and its filter-complex construction, then compare the hot-fix path described in index.ts. Reproduce the supplied ffmpeg command and inspect how the existing audio streams are mixed; done means the main audio track can fade out smoothly when it extends beyond the generated video.