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Commit f9467035 authored by Jennifer's avatar Jennifer
Browse files

Floss: add mmc README.md 

In this patch, README.md is added for project introduction and describe
how to apply MMC to new codec.

Bug: 294165109
Tag: #floss
Test: m - None
Change-Id: I609951bb0167170d73dae2b2b585715ed41875f4
parent 92baba47

system/stack/mmc/README.md

0 → 100644
+45 −0
Original line number Diff line number Diff line 
# Minijailed Media Codec (MMC)



MMC is a service running in minijail that isolates codec implementations from

the Bluetooth process and system resources. It is an independent daemon that

spawns codec servers on demand to communicate with their corresponding codec

clients living in Floss.



## Steps to Apply MMC to a New Codec



### 1. Implement codec server



  * Wraps third party library codes.

  * Codec server should inherit [MMC Interface](https://cs.android.com/android/platform/superproject/main/+/main:packages/modules/Bluetooth/system/stack/mmc/mmc_interface/mmc_interface.h).

    * public methods: `init`, `cleanup`, `transcode`.

    * `init`: set up transcoder and return frame size accepted by the transcoder.

    * `cleanup`: clear the transcoder context.

    * `transcode`: transcode input data, store result in the given output buffer,

                   and return the transcoded data length.



### 2. Add codec proto message in [mmc_config.proto](https://cs.android.com/android/platform/superproject/main/+/main:packages/modules/Bluetooth/system/stack/mmc/proto/mmc_config.proto)



  * Define a proto message for the new codec, generally, it may include:

    * Init configuration.

    * Transcode arguments or params.

    * Library-specific enum mappings.

  * Append an entry to [`ConfigParam`](https://cs.android.com/android/platform/superproject/main/+/main:packages/modules/Bluetooth/system/stack/mmc/proto/mmc_config.proto;drc=1e6b2d44402d18cce637f4b02d4da25133924662;l=99).



### 3. Add codec support in MMC daemon



  * Match the new `ConfigParam` to create its corresponding server in [`CodecInit`](https://cs.android.com/android/platform/superproject/main/+/main:packages/modules/Bluetooth/system/stack/mmc/daemon/service.cc;drc=e9fcc3a7897c6af3df4163534688290778e2333b;l=186).



### 4. Access the interface via [`CodecClient`](https://cs.android.com/android/platform/superproject/main/+/main:packages/modules/Bluetooth/system/stack/mmc/codec_client/codec_client.h) from within the BT process



  * BT process accesses codec implementations via `CodecClient`.

    * `init`: set up `ConfigParam` and pass it to `CodecClient`.

    * `transcode`: pass input and output buffer, and specify the input data size

                   and the output buffer capacity. `transcode` returns transcoded

                   data length on success, and negative error number otherwise.

    * `cleanup`: when a session ends, `cleanup` should be called.



## Related links



* Design doc: go/floss-mmc

* Slides: go/floss-mmc-presentation

* Performance evaluation: go/floss-mmc-experiment