RFC Any interest in collaborating?

I see this code is declared as not working for playback of music files.

I am developing an asynchronous VS1053 driver under MicroPython, based on your code. So far I have tested with MP3 files at 128kbps. It produces glitch-free music. By my calculations there should be plenty of headroom for higher bit rates.

I provide methods to read and write to the I/O pins and cancellation of a playing stream. These have tested OK.

I have the SD card working, but at present playback from the SD card fails: there is a concurrency issue which I haven't yet identified.

My solution differs from yours to support asynchronous behaviour and differences in coding style but I believe there is scope for sharing observations and ideas.

To kick things off I think there is a bug [here](https://github.com/adafruit/Adafruit_CircuitPython_VS1053/blob/0676a052d65a169ca15f42006c1f5f129634b0be/adafruit_vs1053.py#L157) with the indices. It should read
```python
return (self._SCI_SPI_BUFFER[2] << 8) | self._SCI_SPI_BUFFER[3]
```
A significant omission addressed by my driver is the sequence at the end of playback of a track. I would be interested in discussing the strategy for altering the SPI baudrate - my reading of the datasheet suggests a different approach (which works on my hardware instance).

Start with adafruit_vs1053.py at line 157 and verify the reported buffer-index issue against the VS1053 behavior. Then review the discussion about end-of-track playback, SD-card concurrency, and SPI baud-rate changes; the issue needs an agreed scope and validation approach before completion can be defined.

Written by the indexing model from the issue text.