Due to file size constraints I sometimes have to use quite low bitrates. I edit videos to upload to a forum, have to keep my videos under 100 Mb. If for a longer video I can only use about 840 kbps for video and audio combined, 384 kbps stereo audio is not an option.
For compatibility, so the videos play on all devices, I’m doing .mp4 files with h264 video codec and aac audio. If I want to drastically reduce the audio bitrate to, let’s say 64 kbps (mono, of course), what sampling rate should I use? Is there a certain balance I should maintain between bitrate and sampling rate, to prevent it from sounding like a tin can telephone for as low bitrates as possible?
Should I be using another audio codec, other than aac? I don’t know much about these codecs, just noticed that mp3 isn’t on the menu.
If compatibility and AAC codec are important, I recommend 64 kbps and one channel (mono). But if you need to compress the audio even more, pay attention to the opus codec, it sounds very good even at an extremely low bitrate of 32 kbps.
I have no experience in audio but for video if the content is mostly static (like a presentation or app screen recording) try the “Slidedeck (H.264)” export preset, it gives really really good compression so you could keep audio in the 96-128kbps range.
It occured to me that by clicking “disable video” I could relatively quickly do some test exports of a longer video I just finished editing, and check the entire sound track on headphones. For now I’ve decided to go with aac mono, 32000 sampling rate, 64 kbps constant bitrate.
To be honest, I can’t really hear a difference to a higher kbps version. But then again the audio quality of my source material wasn’t very good to begin with, cheap cameras and microphones. I might do some further experiments and look into that opus codec, because I can use all the kbps I can get hold of on the video quality