AudioPolicyManager::getDeviceForStrategy

119 阅读 0 评论 79 点赞

我是靠谱客的博主认真大门，最近开发中收集的这篇文章主要介绍AudioPolicyManager::getDeviceForStrategy，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

getStrategy根据StreamType得到Strategy，AudioPolicyManager再从mOutputRoutes里查出Strategy和前面得到的Strategy相等的Route里面的Device

从以上可以看出， Strategy可以定义为：Group of stream types with the similar behavior。当然从getStrategyForStream函数的定义也可以看出来：

164 routing_strategy Engine::getStrategyForStream(audio_stream_type_t stream)
165 {
166 // stream to strategy mapping
167 switch (stream) {
168 case AUDIO_STREAM_VOICE_CALL:
169 case AUDIO_STREAM_BLUETOOTH_SCO:
170 return STRATEGY_PHONE;
171 case AUDIO_STREAM_RING:
172 case AUDIO_STREAM_ALARM:
173 return STRATEGY_SONIFICATION;
174 case AUDIO_STREAM_NOTIFICATION:
175 return STRATEGY_SONIFICATION_RESPECTFUL;
176 case AUDIO_STREAM_DTMF:
177 return STRATEGY_DTMF;
178 default:
179 ALOGE("unknown stream type %d", stream);
180 case AUDIO_STREAM_SYSTEM:
181 // NOTE: SYSTEM stream uses MEDIA strategy because muting music and switching outputs
182 // while key clicks are played produces a poor result
183 case AUDIO_STREAM_MUSIC:
184 return STRATEGY_MEDIA;
185 case AUDIO_STREAM_ENFORCED_AUDIBLE:
186 return STRATEGY_ENFORCED_AUDIBLE;
187 case AUDIO_STREAM_TTS:
188 return STRATEGY_TRANSMITTED_THROUGH_SPEAKER;
189 case AUDIO_STREAM_ACCESSIBILITY:
190 return STRATEGY_ACCESSIBILITY;
191 case AUDIO_STREAM_REROUTING:
192 return STRATEGY_REROUTING;
193 }
194 }

AudioPolicyManager::getOutputForAttr里有个很重要的数据结构叫

174 typedef struct {
175 audio_content_type_t content_type;
176 audio_usage_t usage;
177 audio_source_t source;
178 audio_flags_mask_t flags;
179 char tags[AUDIO_ATTRIBUTES_TAGS_MAX_SIZE]; /* UTF8 */
180 } audio_attributes_t;

这个参数是从AudioTrack那里一路传过来的，具体参见《 AudioTrack到AudioFlinger再到AudioPolicyService》这篇博客的图。

audio_attributes_t几个字段的解释如下：

usage: why the source is playing (routing, focus volume)

content_type:what the source plays (music, movie, speech, sonification, ...)

Flags: how the source plays(audibility enforcement, AV sync, ...)

getOutputForAttr会调到stream_type_to_audio_attributes，从stream_type_to_audio_attributes可以看出根据streamType就可以找到audio_attributes_t的content_type和usage：

64 static void stream_type_to_audio_attributes(audio_stream_type_t streamType,
65 audio_attributes_t *attr) {
66 memset(attr, 0, sizeof(audio_attributes_t));
67
68 switch (streamType) {
69 case AUDIO_STREAM_DEFAULT:
70 case AUDIO_STREAM_MUSIC:
71 attr->content_type = AUDIO_CONTENT_TYPE_MUSIC;
72 attr->usage = AUDIO_USAGE_MEDIA;
73 break;
74 case AUDIO_STREAM_VOICE_CALL:
75 attr->content_type = AUDIO_CONTENT_TYPE_SPEECH;
76 attr->usage = AUDIO_USAGE_VOICE_COMMUNICATION;
77 break;
78 case AUDIO_STREAM_ENFORCED_AUDIBLE:
79 attr->flags |= AUDIO_FLAG_AUDIBILITY_ENFORCED;
80 // intended fall through, attributes in common with STREAM_SYSTEM
81 case AUDIO_STREAM_SYSTEM:
82 attr->content_type = AUDIO_CONTENT_TYPE_SONIFICATION;
83 attr->usage = AUDIO_USAGE_ASSISTANCE_SONIFICATION;
84 break;
85 case AUDIO_STREAM_RING:
86 attr->content_type = AUDIO_CONTENT_TYPE_SONIFICATION;
87 attr->usage = AUDIO_USAGE_NOTIFICATION_TELEPHONY_RINGTONE;
88 break;
89 case AUDIO_STREAM_ALARM:
90 attr->content_type = AUDIO_CONTENT_TYPE_SONIFICATION;
91 attr->usage = AUDIO_USAGE_ALARM;
92 break;
93 case AUDIO_STREAM_NOTIFICATION:
94 attr->content_type = AUDIO_CONTENT_TYPE_SONIFICATION;
95 attr->usage = AUDIO_USAGE_NOTIFICATION;
96 break;
97 case AUDIO_STREAM_BLUETOOTH_SCO:
98 attr->content_type = AUDIO_CONTENT_TYPE_SPEECH;
99 attr->usage = AUDIO_USAGE_VOICE_COMMUNICATION;
100 attr->flags |= AUDIO_FLAG_SCO;
101 break;
102 case AUDIO_STREAM_DTMF:
103 attr->content_type = AUDIO_CONTENT_TYPE_SONIFICATION;
104 attr->usage = AUDIO_USAGE_VOICE_COMMUNICATION_SIGNALLING;
105 break;
106 case AUDIO_STREAM_TTS:
107 attr->content_type = AUDIO_CONTENT_TYPE_SPEECH;
108 attr->usage = AUDIO_USAGE_ASSISTANCE_ACCESSIBILITY;
109 break;
110 default:
111 ALOGE("invalid stream type %d when converting to attributes", streamType);
112 }
113 }