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最近搞新项目，需要在C++层里实现各种音视频逻辑，在网上下载了FFmpeg等库放入Android Studio后，出现各种问题，现在都汇总记录下~
1.外接UVC协议的摄像头时，插上摄像头后，有显示设备列表，但是就没有画面出来。外接摄像头是用了开源库的LibUvcCamera日志也报这样的错：
[506*UVCCamera.cpp:172:connect]:could not open camera:err=-1
E/AndroidRuntime: FATAL EXCEPTION: BaseActivity
Process: com.serenegiant.usbcameratest0, PID: 7753
java.lang.UnsupportedOperationException: open failed:result=-1
at com.serenegiant.usb.UVCCamera.open(UVCCamera.java:204)
at com.serenegiant.usbcameratest0.MainActivity$2$1.run(MainActivity.java:149)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.os.HandlerThread.run(HandlerThread.java:61)
查了很多资料，都说更换NDK版本，但是我试了不行，后来又查了很多资料，在外国一论坛有个大神说toolchain版本有关，然后看了源码编译的Application.mk刚好注释掉了，所以我去掉注释让其生效：
NDK_TOOLCHAIN_VERSION := 4.9
发现没有报错，也能正常显示画面了，下面附上Application.mk修改后的完整代码：
#/*
# * UVCCamera
# * library and sample to access to UVC web camera on non-rooted Android device
# *
# * Copyright (c) 2014-2017 saki t_saki@serenegiant.com
# *
# * File name: Application.mk
# *
# * 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.
# *
# * All files in the folder are under this Apache License, Version 2.0.
# * Files in the jni/libjpeg, jni/libusb, jin/libuvc, jni/rapidjson folder may have a different license, see the respective files.
#*/
# This is just for mips, if you really needs MSA, un-comment and build with GCC.
# Note: Supporting GCC on NDK is already deprecated and GCC will be removed from NDK soon.
NDK_TOOLCHAIN_VERSION := 4.9
APP_PLATFORM := android-14
#APP_ABI := armeabi armeabi-v7a x86 mips
APP_ABI := armeabi-v7a
#APP_OPTIM := debug
APP_OPTIM := release
2.接着ffmpeg和meadiaCodec相关的库：
error: no type named 'shared_ptr' in namespace 'std'
解决办法，在对应文件加入：#include<memory>
error: no type named 'condition_variable' in namespace 'std'
在报错文件加入：#include <condition_variable>?
error: use of undeclared identifier 'free'
在报错文件头加入：#include <stdlib.h>
最后编译时，因为有很多库相互依赖，会出现这样错误：
More than one file was found with OS independent path 'lib/arm64-v8a/libyuv.so'. If you are using jniLibs and CMake IMPORTED targets
则需在build.gradle加入如下这句：
packagingOptions {
pickFirst 'lib/arm64-v8a/libffmpeg.so'
pickFirst 'lib/arm64-v8a/libyuv.so'
pickFirst 'lib/armeabi-v7a/libyuv.so'
pickFirst 'lib/armeabi-v7a/libffmpeg.so'
}
我这里是提示了才加的，没提示的不用加。
packagingOptions放在android目录里即可
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