这段代码什么意思： audio_io_
handle_t AudioPolicyManager::selectOutputForMusicEffects
()
3567 {
3568 // select one output among several suitable for global effects.
3569 // The priority is as follows:
3570 // 1: An offloaded output. If the effect ends up not being offloadable,
3571 // AudioFlinger will invalidate the track and the offloaded output
3572 // will be closed causing the effect to be moved to a PCM output.
3573 // 2: A deep
buffer output
3574 // 3: The primary output
3575 // 4: the first output in the list
3576
3577 DeviceVector devices = mEngine->getOutputDevicesForAttributes
(
3578 attributes_initializer
(AUDIO_USAGE_MEDIA
), nullptr, false /*fromCache*/
);
3579 SortedVector<audio_io_
handle_t> outputs = getOutputsForDevices
(devices, mOutputs
);
3580
3581 if
(outputs.size
() == 0
) {
3582 return AUDIO_IO_
HANDLE_NONE;
3583 }
3584
3585 audio_io_
handle_t output = AUDIO_IO_
HANDLE_NONE;
3586 bool activeOnly = true;
3587
3588 while
(output == AUDIO_IO_
HANDLE_NONE
) {
3589 audio_io_
handle_t outputOffloaded = AUDIO_IO_
HANDLE_NONE;
3590 audio_io_
handle_t outputDeep
Buffer = AUDIO_IO_
HANDLE_NONE;
3591 audio_io_
handle_t outputPrimary = AUDIO_IO_
HANDLE_NONE;
3592 #ifdef OPLUS_FEATURE_GAME_AUDIO_EFFECTS
3593 // Chuancheng.Dong@MULTIMEDIA.AUDIOSERVER.FRAMEWORK, 2022/07/14, support music effects for fast output
3594 audio_io_
handle_t outputFast = AUDIO_IO_
HANDLE_NONE;
3595 #endif /* OPLUS_FEATURE_GAME_AUDIO_EFFECTS */
3596
3597 for
(audio_io_
handle_t output : outputs
) {
3598 sp<SwAudioOutputDescriptor> desc = mOutputs.valueFor
(output
);
3599 if
(activeOnly && !desc->isActive
(toVolumeSource
(AUDIO_STREAM_MUSIC
))) {
3600 continue;
3601 }
3602 ALOGV
("selectOutputForMusicEffects activeOnly %d output %d flags 0x%08x",
3603 activeOnly, output, desc->mFlags
);
3604 if
((desc->mFlags & AUDIO_OUTPUT_FLAG_COMPRESS_OFFLOAD
) != 0
) {
3605 outputOffloaded = output;
3606 }
3607 if
((desc->mFlags & AUDIO_OUTPUT_FLAG_DEEP_
BUFFER) != 0
) {
3608 outputDeep
Buffer = output;
3609 }
3610 if
((desc->mFlags & AUDIO_OUTPUT_FLAG_PRIMARY
) != 0
) {
3611 outputPrimary = output;
3612 }
3613 #ifdef OPLUS_FEATURE_GAME_AUDIO_EFFECTS
3614 // Chuancheng.Dong@MULTIMEDIA.AUDIOSERVER.FRAMEWORK, 2022/07/14, support music effects for fast output
3615 if
(((desc->mFlags & AUDIO_OUTPUT_FLAG_FAST
) != 0
)
3616 &&
((desc->mFlags & AUDIO_OUTPUT_FLAG_PRIMARY
) == 0
)) {
3617 outputFast = output;
3618 }
3619 #endif /* OPLUS_FEATURE_GAME_AUDIO_EFFECTS */
3620 }
3621 if
(outputOffloaded != AUDIO_IO_
HANDLE_NONE
) {
3622 output = outputOffloaded;
3623 } else if
(outputDeep
Buffer != AUDIO_IO_
HANDLE_NONE
) {
3624 output = outputDeep
Buffer;
3625 } else if
(outputPrimary != AUDIO_IO_
HANDLE_NONE
) {
3626 output = outputPrimary;
3627 #ifdef OPLUS_FEATURE_GAME_AUDIO_EFFECTS
3628 // Chuancheng.Dong@MULTIMEDIA.AUDIOSERVER.FRAMEWORK, 2022/07/14, support music effects for fast output
3629 } else if
(outputFast != AUDIO_IO_
HANDLE_NONE
) {
3630 output = outputFast;
3631 #endif /* OPLUS_FEATURE_GAME_AUDIO_EFFECTS */
3632 } else {
3633 output = outputs[0];
3634 }
3635 activeOnly = false;
3636 }
3637
3638 #ifdef OPLUS_FEATURE_GAME_AUDIO_EFFECTS
3639 // Chuancheng.Dong@MULTIMEDIA.AUDIOSERVER.FRAMEWORK, 2020/06/06, Add for music effects moving policy
3640 mAudioPolicyManagerExt->oplusSelectOutputForMusicEffects
(output, mMusicEffectOutput, mOutputs, outputs, mEffects
);
本文详细介绍了C++中native_handle_t和buffer_handle_t的定义、作用以及应用场景，包括它们在系统核心库中的位置和使用方式。通过实例解析，帮助读者理解并掌握这两个关键数据类型的应用。
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