ShockAudio _{(Will probably change name later)}

This firmware is used to make a network/bluetooth speaker using an ESP32. Plan is to make a custom PCB as well.

Todo

Upgrade to new audio_element system:

• Write a generic audio_element struct/system, which makes use of callback functions to do the actual work. (read/write buffers, init/deinit interfaces)
• Convert sdcard source to the new system
  • Still a bit crude
• Convert bluetooth source to the new system
  • A2DP part
  • AVRCP part
  • This needs to be implemented more (state change, save pos in info struct, etc.), but it is converted to the new system.
• Convert tone source to the new system
  • This needs a rewrite anyways
• For now Add a way to have multiple inputs/outputs
  • Many > one will just be the mixer (e.g. mixer_add_element()).
  • One > Many has to be a new element type? This will be necessary if you want to send the data to multiple streams (e.g. i2s and tcp).
• Convert mixer to the new system and add support for multiple input streams
• Update: Add 'user data' var to io_t struct which will hold the AEL info_t struct corresponding to that specific buffer
  • Done, Needs testing though
  • This is probably not the best way to do this. I am thinking about just taking the control and info parts out of the audio_element completely.
• ! Add a way to pause AEL threads (infinite loops from clogging the cpu)

General:

• Sources should write directly to the context buffer, not first write to an intermediate buffer.
  • This will safe quite some memory.
  • This can be done now with the new io_t struct. Give the input of the next element the output of the previous element.
• Split mixer, so that it only mixes the data, not send it to the renderer. Or at least return the data somehow.
  • This is required to stream the data to other sinks as well.
  • Done as a result of the new AEL system
• Think about how the sources are interacting with their context
  • Directly or through helper functions?
  • Now it's a mix of both and it's a mess.
  • Done as a result of the new AEL system
• Add some status management (Playing, paused, stopped, etc.)
  • Pausing a source should preferably pause the task itself.
  • When setting status to 'stopped' the task should stop. To start it again, the init function has to be called again.
• Create decoders (mp3, aac(?) and ogg vorbis (spotify))
  • Add codec_type to info struct.
  • Have decoder just pass input to output if no decoding necessary.

Bluetooth:

• SBC is pretty good, see [2]
• Add some proper volume handling
• Add some proper metadata handling (with posibility to export data for e.g. display)
• Add ability for media control from sink
• SSP

Tone:

• Add different waveforms?
• Add a simple delay
• Add some structure to create melodies or tunes
• Add option to set the bits per sample?
  • It now always has a bits per sample of 8, which is probably fine.

Resampling/bitdepth:

• Take another look at upsampling.
• Downsampling?
  • Might not be needed, since it is always better to upsample other sources, than to downsample a high SR source.
  • It can be useful when streaming the data to another sink though.
• Write code to transform bitdepth

SDCard:

• Add option to have multiple files playing back
  • Can be useful to simultaneously play back music and some notification sound.

Advanced:

• Add some wifi capabilities
  • Spotify?
  • Chromecast?
• Add spotify connect support
• Add some way for multiple devices to communicate and sync audio (a la sonos)
• Add battery management and battery notification sounds

Interesting reads

• [1]: Audio over Bluetooth: most detailed information about profiles, codecs, and devices
• [2]: Bluetooth stack modifications to improve audio quality on headphones without AAC, aptX, or LDAC codecs