Video editing app for lowering background noise while evidentiating slow voice?

Solution 1:

To get a good noise reduction we cannot simply rely on basic denoise filters, as these may not be much more than low or high pass filters which then may lead to a rather muffled result.

A better approach will be using a dedicated audio processor designed to have good noise reduction algorithms on the audio content of our video only.

To do so the following short tutorial uses Audacity for audio processing, and FFmpeg for audio extraction and rebuilding the video.

1. Extract the audio from our video file
   To keep the original's audio encoding we need to find out what codec the audio of our video file uses. This will e.g. be displayed on the right click file Properties > Video/Audio tab. You e.g will find it is AAC or mp3 encoded. Then we can extract the audio of an mp4 file with the following command:

    ffmpeg -i infile.mp4 -acodec copy outfile.aac
   

The option -acodec copy says we do not resample audio

2. Use Audacity's noise reduction filters:

• How to improve the sound quality of an mp3 speech file?

3. Merge audio and video again.

Again, to avoid resampling we need the option copy to just use the data as they are. The source video's audio track will be remapped to the denoised sample with the following command:

    ffmpeg -i infile.mp4 -i denoised-audio.m4a -vcodec copy -acodec copy -map 0:0 -map 1:0 denoised-video.mp4

Solution 2:

So the audio level needs to be 'compressed', that is, the loudest and the quietest volumes need to be brought closer together. That could be done manually by someone 'riding the gain' (manually adjusting the audio level, or Audacity does that automatically for audio).

However, you need to keep the audio synchronized with the video, and Audacity won't do video, so I suggest you register at the Avidemux forum and post your question there, for Avidemux is the most popular video-audio editor for Linux (based on frequency of http://SourceForge.net downloads).

There's also a list of other video+audio editors here on Video editing software options? and from the screenshot, PITIVI will also do what you need.