1# Camera Metadata 2 3Metadata is the description and context of image information returned by the camera application. It provides detailed data for the image information, for example, coordinates of a viewfinder frame for identifying a portrait in a photo or a video. 4 5Metadata uses a tag (key) to find the corresponding data during the transfer of parameters and configurations, reducing memory copy operations. 6 7## How to Develop 8 9Read [Camera](../reference/apis/js-apis-camera.md) for the API reference. 10 111. Import the modules. 12 ```ts 13 import camera from '@ohos.multimedia.camera'; 14 import { BusinessError } from '@ohos.base'; 15 ``` 16 172. Obtain the metadata types supported by the current device from **supportedMetadataObjectTypes** in **CameraOutputCapability**, and then use **createMetadataOutput()** to create a metadata output stream. 18 19 ```ts 20 function getMetadataOutput(cameraManager: camera.CameraManager, cameraOutputCapability: camera.CameraOutputCapability): camera.MetadataOutput | undefined { 21 let metadataObjectTypes: Array<camera.MetadataObjectType> = cameraOutputCapability.supportedMetadataObjectTypes; 22 let metadataOutput: camera.MetadataOutput | undefined = undefined; 23 try { 24 metadataOutput = cameraManager.createMetadataOutput(metadataObjectTypes); 25 } catch (error) { 26 let err = error as BusinessError; 27 console.info('Failed to createMetadataOutput, error code: '+ err.code); 28 } 29 return metadataOutput; 30 } 31 ``` 32 333. Call **start()** to start outputting metadata. If the call fails, an error code is returned. For details, see [Camera Error Codes](../reference/apis/js-apis-camera.md#cameraerrorcode). 34 35 ```ts 36 function startMetadataOutput(metadataOutput: camera.MetadataOutput): void { 37 metadataOutput.start().then(() => { 38 console.info('Callback returned with metadataOutput started.'); 39 }).catch((err: BusinessError) => { 40 console.info('Failed to metadataOutput start, error code: '+ err.code); 41 }); 42 } 43 ``` 44 454. Call **stop()** to stop outputting metadata. If the call fails, an error code is returned. For details, see [Camera Error Codes](../reference/apis/js-apis-camera.md#cameraerrorcode). 46 47 ```ts 48 function stopMetadataOutput(metadataOutput: camera.MetadataOutput): void { 49 metadataOutput.stop().then(() => { 50 console.info('Callback returned with metadataOutput stopped.'); 51 }).catch((err: BusinessError) => { 52 console.info('Failed to metadataOutput stop '+ err.code); 53 }); 54 } 55 ``` 56 57## Status Listening 58 59During camera application development, you can listen for the status of metadata objects and output stream. 60 61- Register the 'metadataObjectsAvailable' event to listen for metadata objects that are available. When a valid metadata object is detected, the callback function returns the metadata. This event can be registered when a **MetadataOutput** object is created. 62 63 ```ts 64 function onMetadataObjectsAvailable(metadataOutput: camera.MetadataOutput): void { 65 metadataOutput.on('metadataObjectsAvailable', (err: BusinessError, metadataObjectArr: Array<camera.MetadataObject>) => { 66 console.info(`metadata output metadataObjectsAvailable`); 67 }); 68 } 69 ``` 70 71 > **NOTE** 72 > 73 > Currently, only **FACE_DETECTION** is available for the metadata type. The metadata object is the rectangle of the recognized face, including the x-axis coordinate and y-axis coordinate of the upper left corner of the rectangle as well as the width and height of the rectangle. 74 75- Register the 'error' event to listen for metadata stream errors. The callback function returns an error code when an API is incorrectly used. For details about the error code types, see [Camera Error Codes](../reference/apis/js-apis-camera.md#cameraerrorcode). 76 77 ```ts 78 function onMetadataError(metadataOutput: camera.MetadataOutput): void { 79 metadataOutput.on('error', (metadataOutputError: BusinessError) => { 80 console.info(`Metadata output error code: ${metadataOutputError.code}`); 81 }); 82 } 83 ``` 84