Googling the key phrase “Native FFmpeg AAC Encoder does not do CBR audio encoding” brings even more discussions to light: CBR Audio … does it work in shotcut forum. Also worth to read is what others say in the avidemux forum and in the audacity discussion.
Inspiringly the audacity team decided to change their settings dialogs in their user interface, to avoid misleading their users by well established terms like CBR and VBR which have a different meaning in FFmpeg. They offer bit rates to choose from, which they found out empirically.
Similar should be taken into account for the Shotcut UI: Why not reveal in the Audio tab of the advanced export dialog what Shotcut is doing in the background? In the dialog tab instead of just “aac” it should be indicated for transparency that the FFmpeg native AAC codec is used, and the -b:a and -q:a parameters will be called.
I wouldn’t let users believe they get CBR while all insiders are in agreement, that the outcome is different from that. Instead, I would avoid the established term “Constant Bitrate” at all (even if the author of the FFmpeg wiki uses it, because he or she revoces that in the next sentence). Better name this option “-b:a Average Bitrate (recommended)”.
Also, I would change the option “Quality based VBR” to “-q:a Variable Bitrate (experimental)” with reference to the FFmpeg wiki, because it is in fact nothing more than experimental, as it is known from several sources. It is definitely not quality based, nore is it content driven. In fact it is complex-conditional and not recommended.
Finally, the “Bitrate b/s” field should get adjusted dropdown choices within the range of 196k…233k for stereo and 98k…160k for mono (ref. audacity). They say the compilations for Win and MacOS behave slightly different (which is negligible), and in combination with video encoding the behavior could be different (I didn’t test that).
Thank you for authoring and maintaining the Shotcut project, and thank you for your support in the forum. Please recognize my constructive criticism as a contribution, I spent hours on research and writing.