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- Raw streams from Android.
- Can we get the raw streams from any source, app, system, etc sent outside of the system without unnecessary preprocessing (see definition of Raw Stream below).
- How is this done?
- Are there limitations? For example, if apps themselves take decision on type, priority, effects, and even volume, then this is not a pure raw stream
- What Raw Stream Metadata (definition below) can be extracted and delivered together with the stream to an outside system.
- Input streams to Android (external sources need to be brought into the Android head unit, if all mixing is done inside Android).
- How is this done?
- Are there limitations on the number of streams?
- Can we bring the required metadata in (or at least associate "hard coded" metadata with the identity of a particular incoming stream. For example we know this one is a prioritised prioritized type of stream)
- Any particular support in Android for networked audio? Audio output device?
- Anything to consider about compressed audio / codecs? Support for hardware implementations?
- → Not in AOSP. The connection to hardware accelerators is expected to be implemented by vendor.
Investigation Answers
- Raw streams:
- Streams have properties. It seems any of these encodings might be used in the HAL interface: https://source.android.com/devices/audio/data_formats
- ...but not all compressions might be supported in a particular platform?
- Bartosz to continue here
- Wassim to continue on metadata availability https://source.android.com/devices/audio/attributes
- Streams have properties. It seems any of these encodings might be used in the HAL interface: https://source.android.com/devices/audio/data_formats
- Input streams to Android
- ... todo...
Analysis of both approaches
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- = The audio stream as coming from a source (PCM format assumed, but might possibly use mostly, or other encoding such as Dolby for multi-channel, in that case indicate this).
- There shall be none or minimal application of Gain/Volume (stream should be at nominal / maximum volume), Effects (no effects applied), or Mixing (one stream at a time).
- We can however consider 2-ch stereo, or multi-channel, as a single stream as long as it is transferred so that it can be trivially separated for treating the channels separately in the outside system.
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