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Commit 0c54edb6 authored by Cheney Ni's avatar Cheney Ni
Browse files

A2DP: AAC encoding counter errata 

When the encoder interval is 23 milliseconds per tick for {44.1 kHz /
16 bits per sample / Stereo}, 3 microseconds shift every tick would
cause one AAC frame mismatched after 180 seconds. Here try to adjust the
timeline to increase the accuracy by following methods:

1. add the remainder back to the timeline when converting the time
   period to data size.
2. change the timestamp to be presented by values in 1/10 microseconds.

Bug: 149546181
Test: manually
Change-Id: I16742042ba64a9355c39c0248be9208567312a9f
Merged-In: I16742042ba64a9355c39c0248be9208567312a9f
(cherry picked from commit bae2582df32576f8e95aa78f039fcfdecc962086)
parent 4c2bf502

system/stack/a2dp/a2dp_aac_encoder.cc

+27 −12
Original line number Diff line number Diff line
@@ -19,6 +19,7 @@ 
#include "a2dp_aac_encoder.h"



#include <inttypes.h>

#include <math.h>

#include <stdio.h>

#include <string.h>
@@ -56,8 +57,8 @@ typedef struct { 


typedef struct {

  uint32_t counter;

  uint32_t bytes_per_tick; /* pcm bytes read each media task tick */

  uint64_t last_frame_us;

  uint32_t bytes_per_tick;              // pcm bytes read each media task tick

  uint64_t last_frame_timestamp_100ns;  // values in 1/10 microseconds

} tA2DP_AAC_FEEDING_STATE;



typedef struct {
@@ -537,16 +538,30 @@ static void a2dp_aac_get_num_frame_iteration(uint8_t* num_of_iterations, 
  LOG_VERBOSE(LOG_TAG, "%s: pcm_bytes_per_frame %u", __func__,

              pcm_bytes_per_frame);



  uint32_t us_this_tick = a2dp_aac_encoder_interval_ms * 1000;

  uint64_t now_us = timestamp_us;

  if (a2dp_aac_encoder_cb.aac_feeding_state.last_frame_us != 0)

    us_this_tick =

        (now_us - a2dp_aac_encoder_cb.aac_feeding_state.last_frame_us);

  a2dp_aac_encoder_cb.aac_feeding_state.last_frame_us = now_us;



  a2dp_aac_encoder_cb.aac_feeding_state.counter +=

      a2dp_aac_encoder_cb.aac_feeding_state.bytes_per_tick * us_this_tick /

      (a2dp_aac_encoder_interval_ms * 1000);

  uint32_t hecto_ns_this_tick = a2dp_aac_encoder_interval_ms * 10000;

  uint64_t* last_100ns =

      &a2dp_aac_encoder_cb.aac_feeding_state.last_frame_timestamp_100ns;

  uint64_t now_100ns = timestamp_us * 10;

  if (*last_100ns != 0) {

    hecto_ns_this_tick = (now_100ns - *last_100ns);

  }

  *last_100ns = now_100ns;



  uint32_t bytes_this_tick =

      a2dp_aac_encoder_cb.aac_feeding_state.bytes_per_tick *

      hecto_ns_this_tick / (a2dp_aac_encoder_interval_ms * 10000);

  a2dp_aac_encoder_cb.aac_feeding_state.counter += bytes_this_tick;

  // Without this erratum, there was a three microseocnd shift per tick which

  // would cause one frame mismatched after every 180 seconds

  uint32_t erratum_100ns =

      ceil(1.0f * bytes_this_tick * a2dp_aac_encoder_interval_ms * 10000 /

           a2dp_aac_encoder_cb.aac_feeding_state.bytes_per_tick);

  if (erratum_100ns < hecto_ns_this_tick) {

    LOG_VERBOSE(LOG_TAG,

                "%s: hecto_ns_this_tick=%d, bytes=%d, erratum_100ns=%d",

                __func__, hecto_ns_this_tick, bytes_this_tick, erratum_100ns);

    *last_100ns -= hecto_ns_this_tick - erratum_100ns;

  }



  result = a2dp_aac_encoder_cb.aac_feeding_state.counter / pcm_bytes_per_frame;

  a2dp_aac_encoder_cb.aac_feeding_state.counter -= result * pcm_bytes_per_frame;