Stereo MP3 Playback: Duplicate Left Channel to Both I2S Output Channels

[Stass48]

I have a question regarding stereo MP3 playback. Specifically, I would like to know if it is possible to route the left audio channel of a stereo MP3 file to both channels of the I2S output (i.e., duplicate the left channel to both left and right outputs).

Questions:
1. Does the library currently support this type of channel routing?
2. If it does, could you please provide guidance on how to achieve this configuration?

Feature Request (if not supported):
If this feature is not currently available, I kindly request its implementation. This functionality would be helpful in setups where mono output is needed or to ensure compatibility with certain audio systems.

Environment:
• Microcontroller: Raspberry Pi Pico (RP2040)
• Core: Earle Philhower’s RP2040 Arduino Core
• Audio Output: I2S via PCM5102

[earlephilhower]

1. No, no downmixing or channel duplication.
   1.a. It's a trivial addition to the ApplyGain method (since it's already touching each sample) or elsewhere, PRs would be appreciated.