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diff --git a/zh-cn/devices/camera/external-usb-cameras.html b/zh-cn/devices/camera/external-usb-cameras.html new file mode 100644 index 00000000..ca46ac55 --- /dev/null +++ b/zh-cn/devices/camera/external-usb-cameras.html @@ -0,0 +1,147 @@ +<html devsite><head> + + <meta name="book_path" value="/_book.yaml"/> + + <meta name="project_path" value="/_project.yaml"/> +</head> +<body> +<!-- + Copyright 2018 The Android Open Source Project + + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> + +<h1 id="external_usb_cameras" class="page-title">外接 USB 摄像头</h1> + +<p>Android 平台支持使用即插即用的 USB 摄像头(例如网络摄像头),但前提是这些摄像头采用标准的 <a href="https://developer.android.com/reference/android/hardware/camera2/package-summary.html">Android Camera2 API</a> 和摄像头 <a href="/reference/hidl/android/hardware/camera/provider/2.4/ICameraProvider">HIDL</a> 接口。网络摄像头通常支持 <a href="https://en.wikipedia.org/wiki/USB_video_device_class">USB 视频类 (UVC)</a> 驱动程序,并且在 Linux 上,系统采用标准的 <a href="https://en.wikipedia.org/wiki/Video4Linux">Video4Linux (V4L)</a> 驱动程序控制 UVC 摄像头。</p> + +<p>如果系统支持网络摄像头,设备便可用于视频聊天和照片冲印机等轻量级用例。此功能并不是为了替代 Android 手机上典型的内部摄像头 HAL,也不是为了协助执行涉及高分辨率和高速流式传输、AR 以及手动 ISP/传感器/智能镜头控制的性能密集型复杂任务。</p> + +<p>全新的 USB 摄像头 HAL 进程是外接摄像头提供程序的一部分,该提供程序会监听 USB 设备可用性,并相应地枚举外接摄像头设备。该进程具有与内置摄像头 HAL 进程类似的权限和 SE 策略。直接与 USB 设备通信的第三方网络摄像头应用访问 UVC 设备时所需的摄像头权限与所有常规摄像头应用所需的权限相同。</p> + +<h2 id="examples_and_sources">示例和源代码</h2> + +<p>要详细了解如何实现 USB 摄像头,请参阅 <a href="https://android.googlesource.com/platform/hardware/interfaces/+/master/camera/provider/2.4/default/"><code>ExternalCameraProvider</code></a> 中的外接摄像头提供程序参考实现。外接摄像头设备和会话实现包含在 <a href="https://android.googlesource.com/platform/hardware/interfaces/+/master/camera/device/"><code>ExternalCameraDevice</code></a> 和 <a href="https://android.googlesource.com/platform/hardware/interfaces/+/master/camera/device/"><code>ExternalCameraDeviceSession</code></a> 中。Java 客户端 API 包含一个新的 <a href="https://developer.android.com/reference/android/hardware/camera2/CameraMetadata?authuser=3#INFO_SUPPORTED_HARDWARE_LEVEL_EXTERNAL"><code>EXTERNAL</code></a> 硬件级别。</p> + +<h2 id="implementation">实现</h2> + +<p>实现必须支持 <a href="https://developer.android.com/guide/topics/connectivity/usb/host"><code>android.hardware.usb.host</code></a> 系统功能。</p> + +<p>此外,还必须启用对 UVC 设备的内核支持。您可以通过将以下内容添加到相应的内核 <code>deconfig</code> 文件来启用该支持。</p> +<pre class="prettyprint"><code>+CONFIG_USB_VIDEO_CLASS=y ++CONFIG_MEDIA_USB_SUPPORT=y +</code></pre><aside class="note"><strong>注意</strong>:<span>请确保您还针对 uvcvideo 安装了这个<a href="https://patchwork.kernel.org/patch/6874491/">补丁程序</a>。</span></aside> +<p>要在相应的设备细分版本中启用外接摄像头提供程序,以便添加必要的 SELinux 权限、外接摄像头配置以及外接摄像头提供程序依赖项,请完成以下步骤:</p> + +<ul> +<li><p>将外接摄像头配置文件和外接摄像头库添加到 <code>device.mk</code></p> +<pre class="prettyprint"><code>+PRODUCT_PACKAGES += android.hardware.camera.provider@2.4-impl ++PRODUCT_PACKAGES += android.hardware.camera.provider@2.4-external-service + ++PRODUCT_COPY_FILES += \ ++device/manufacturerX/productY/external_camera_config.xml:$(TARGET_COPY_OUT_VENDOR)/etc/external_camera_config.xml +</code></pre></li> +<li><p>将外接摄像头提供程序名称添加到设备 Treble HAL 清单</p> +<pre class="prettyprint"><code><hal format="hidl"> + <name>android.hardware.camera.provider</name> + <transport arch="32+64">passthrough</transport> + <impl level="generic"></impl> + <version>2.4</version> + <interface> + <name>ICameraProvider</name> + <instance>legacy/0</instance> ++ <instance>external/0</instance> + </interface> +</hal> +</code></pre></li> +<li><p>(选做)如果设备在 Treble 直通模式下运行,请更新 <code>sepolicy</code>,以便 <code>cameraserver</code> 可以访问 UVC 摄像头</p> +<pre class="prettyprint"><code>+# for external camera ++allow cameraserver device:dir r_dir_perms; ++allow cameraserver video_device:dir r_dir_perms; ++allow cameraserver video_device:chr_file rw_file_perms; +</code></pre></li> +</ul> + +<p>以下是 <code>external_camera_config.xml</code> 的示例(省略了版权行)</p> +<pre class="prettyprint"><code><ExternalCamera> + <Provider> + <!-- Internal video devices to be ignored by external camera HAL --> + <id>0</id> <!-- No leading/trailing spaces --> + <id>1</id> + + </Provider> + <!-- See ExternalCameraUtils.cpp for default values of Device configurations below --> + <Device> + <!-- Max JPEG buffer size in bytes--> + <MaxJpegBufferSize bytes="3145728"/> <!-- 3MB (~= 1080p YUV420) --> + <!-- Size of v4l2 buffer queue when streaming >= 30fps --> + <!-- Larger value: more request can be cached pipeline (less janky) --> + <!-- Smaller value: use less memory --> + <NumVideoBuffers count="4"/> + <!-- Size of v4l2 buffer queue when streaming < 30fps --> + <NumStillBuffers count="2"/> + + <!-- List of maximum fps for various output sizes --> + <!-- Any image size smaller than the size listed in Limit row will report + fps (as minimum frame duration) up to the fpsBound value. --> + <FpsList> + <!-- width/height must be increasing, fpsBound must be decreasing--> + <Limit width="640" height="480" fpsBound="30.0"/> + <Limit width="1280" height="720" fpsBound="15.0"/> + <Limit width="1920" height="1080" fpsBound="10.0"/> + <!-- image size larger than the last entry will not be supported--> + </FpsList> + </Device> +</ExternalCamera> +</code></pre> +<h2 id="customization">自定义</h2> + +<p>您可以通过常规自定义选项或设备专用的优化来提升 Android 摄像头的性能。</p> + +<h3 id="general_customizations">常规自定义</h3> + +<p>您可以通过修改 <code>external_camera_config.xml</code> 文件来自定义外接摄像头提供程序。具体而言,客户可以自定义以下参数:</p> + +<ul> +<li>内部摄像头的排除视频节点</li> +<li>支持的图片大小和帧速率上限</li> +<li>Inflight 缓冲区数量(在卡顿与内存之间进行权衡)</li> +</ul> + +<p>除了这些参数之外,您还可以添加自己的参数或开发自己的配置。</p> + +<h3 id="device_specific_optimizations">设备专用的优化</h3> + +<p>您还可以通过添加设备专用的优化来提升性能。</p> + +<h4 id="buffer_copyscaling_and_jpeg_decodeencode">缓冲区复制/调整大小和 JPEG 解码/编码</h4> + +<p>通用实现使用的是 CPU (libyuv/libjpeg),但您可以将其替换为设备专用的优化。</p> + +<h4 id="hal_output_format">HAL 输出格式</h4> + +<p>通用实现采用以下输出格式:</p> + +<ul> +<li>YUV_420_888:适用于视频 IMPLEMENTATION_DEFINED 缓冲区。</li> +<li>YV12:适用于所有其他 IMPLEMENTATION_DEFINED 缓冲区。</li> +</ul> + +<p>为了提升性能,您可以将输出格式替换为设备专用的高效格式。此外,您还可以在自定义的实现中支持其他格式</p> + +<h2 id="validation">验证</h2> + +<p>支持外接摄像头的设备必须通过摄像头 CTS 测试。在整个测试运行期间,外接 USB 网络摄像头必须始终插入到特定设备,否则某些测试用例会失败。</p> +<aside class="note"><strong>注意</strong>:<span><code>media_profiles</code> 条目不适用于外接 USB 网络摄像头,因此没有 <a href="https://developer.android.com/reference/android/media/CamcorderProfile">camcorder 配置文件</a>。</span></aside> + +</body></html>
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