2023年7月7日发(作者：)

android 移植ffmpeg后so库的使用

今天折腾了一天，可算是有所收获，成功的用jni调用了libffmpeg中的一个方法-----avcodec_version()，至于avcodec_version()是干什么用的我不大清楚，应该是获取版本信息吧，没有深入的去研究ffmpeg。

这里主要是想把折腾一天所获取的经验记录下来，以免时间长全忘了，也希望能给其他人一点借鉴，不至于和我一样一点头绪都没有连猜带蒙的，本文纯属个人心得，高手可以无视....

要在android上用ffmpeg首先得奖ffmpeg工程移植到android上，这里就要用到ndk把这个开源工程编译成一个后缀为so的库，这个步骤这里就不多说了 网上的资料也挺多的，我是按照:/scottwong/archive/2010/12/17/在ubantu环境下编译的，你按照教程上一步一步来应该都没有问题，顺便给下在windows下编译ffmpeg的教程：/compile-ffmpeg-android-ndk（这个要用非ie浏览器打开）。以上两篇文章给了我很大的指引，在此谢过。。。都是牛人啊~~~

编译完以后你会获得一个的文件，那么问题来了，怎么用呢。我在百度，google搜了半天也没有一个详细的教程，总是东一句西一句的，但思路是明确的，就是还得编译一个so文件，这个so里的是jni方法，可以由java层调用的，而这些jni方法里用到的函数则就是来至了。思路是有了，但是具体怎么做呢？又经过一顿摸索，n次的编译，终于编译成功了。我是拿一个标准的ndk例子来做的测试就是ndk samples文件夹里的hello-jni工程。进入该工程的jni目录，将ffmpeg的源代码拷到该目录下，做这部的原因是你要编译的so文件里需要调用ffmpeg的方法，自然要引用ffmpeg里的h文件，然后将文件拷到ndk目录下的platforms/android-5/arch-arm/usr/lib目录下(你会发现platfroms里有好几个android文件夹如 -3 -4 -5分别代表不同的版本，以防万一我每个目录都拷了，呵呵，应该是只要拷指定目录的)，因为等等系统编译的时候要用。接下来就编辑和hello-jni.c文件了 代码如下

C代码

1. # Copyright (C) 2009 The Android Open Source Project

2. #

3. # Licensed under the Apache License, Version 2.0 (the "License");

4. # you may not use this file except in compliance with the License.

5. # You may obtain a copy of the License at

6. #

7. # /licenses/LICENSE-2.0 8. #

9. # Unless required by applicable law or agreed to in writing,

software

10.# distributed under the License is distributed on an "AS IS" BASIS,

11.# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or

implied.

12.# See the License for the specific language governing permissions

and

13.# limitations under the License.

14.#

_PATH := $(call my-dir)

16.

e $(CLEAR_VARS)

_TO_FFMPEG_SOURCE:=$(LOCAL_PATH)/ffmpeg

_C_INCLUDES += $(PATH_TO_FFMPEG_SOURCE)

_LDLIBS := -lffmpeg

_MODULE := hello-jni

_SRC_FILES := hello-jni.c

23.

e $(BUILD_SHARED_LIBRARY)

PATH_TO_FFMPEG_SOURCE:=$(LOCAL_PATH)/ffmpeg

这行是定义一个变量，也就是ffmpeg源码的路径

LOCAL_C_INCLUDES += $(PATH_TO_FFMPEG_SOURCE)

这行是指定源代码的路径，也就是刚才拷过去的ffmpeg源码，$(LOCAL_PATH)是根目录，如果没有加这行那么引入ffmpeg库中的h文件编译就会出错说找不到该h文件。

LOCAL_LDLIBS := -lffmpeg

这行很重要，这是表示你这个so运行的时候依赖于这个库， 再举个例子：如果你要编译的so不仅要用到这个库还要用的这个库的话，你这个参数就应该写成

LOCAL_LDLIBS := -lffmpeg -lopencv

其他的参数都是正常的ndk编译用的了，不明白的话google一下。

hello-jni.c

C代码

1. /*

2. * Copyright (C) 2009 The Android Open Source Project 3. *

4. * Licensed under the Apache License, Version 2.0 (the "License");

5. * you may not use this file except in compliance with the License.

6. * You may obtain a copy of the License at

7. *

8. * /licenses/LICENSE-2.0

9. *

10.* Unless required by applicable law or agreed to in writing,

software

11.* distributed under the License is distributed on an "AS IS" BASIS,

12.* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or

implied.

13.* See the License for the specific language governing permissions

and

14.* limitations under the License.

15.*

16.*/

17.#include

18.#include

19.#include

20.#include

21.#include

22.#include

23./* This is a trivial JNI example where we use a native method

24.* to return a new VM String. See the corresponding Java source

25.* file located at:

26.*

27.*

apps/samples/hello-jni/project/src/com/example/HelloJni/

28.*/

g

_com_example_hellojni_HelloJni_stringFromJNI( JNIEnv* env,

t thiz )

32.{

str[25];

f(str, "%d", avcodec_version());

35.

36.

(*env)->NewStringUTF(env, str);

38.}

#include

这行是因为下面要用到avcodec_version()这个函数。 改完这两个文件以后就可以编译了~~用ndk-build命令编译完后在工程的libs/armeabi目录底下就会有一个文件了！（两行眼泪啊~终于编译成功了）

编译完成后就可以进行测试了，记得将也拷到armeabi目录底下，并在java代码中写上

Java代码

1. static {

2. brary("ffmpeg");

3. brary("hello-jni");

4. }

Java代码

1. /*

2. * Copyright (C) 2009 The Android Open Source Project

3. *

4. * Licensed under the Apache License, Version 2.0 (the "License");

5. * you may not use this file except in compliance with the License.

6. * You may obtain a copy of the License at

7. *

8. * /licenses/LICENSE-2.0

9. *

10.* Unless required by applicable law or agreed to in writing,

software

11.* distributed under the License is distributed on an "AS IS" BASIS,

12.* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or

implied.

13.* See the License for the specific language governing permissions

and

14.* limitations under the License.

15.*/

e ni;

17.

ty;

ew;

;

21.

22.

class HelloJni extends Activity

24.{ 25./** Called when the activity is first created. */

26.@Override

void onCreate(Bundle savedInstanceState)

28.{

te(savedInstanceState);

30.

31./* Create a TextView and set its content.

32.* the text is retrieved by calling a native

33.* function.

34.*/

ew tv = new TextView(this);

t( "1111" );

37.//n();

tentView(tv);

t(f(stringFromJNI()));

40.}

41.

42./* A native method that is implemented by the

43.* 'hello-jni' native library, which is packaged

44.* with this application.

45.*/

native String stringFromJNI();

47.

48./* This is another native method declaration that is *not*

49.* implemented by 'hello-jni'. This is simply to show that

50.* you can declare as many native methods in your Java code

51.* as you want, their implementation is searched in the

52.* currently loaded native libraries only the first time

53.* you call them.

54.*

55.* Trying to call this function will result in a

56.* sfiedLinkError exception !

57.*/

native String unimplementedStringFromJNI();

59.

60./* this is used to load the 'hello-jni' library on application

61.* startup. The library has already been unpacked into

62.* /data/data/ni/lib/ at

63.* installation time by the package manager.

64.*/

{

brary("ffmpeg");

brary("hello-jni");

68.} 69.}

到此就完成了，将程序装到手机可看到打印出“3426306”，google搜索“ffmpeg 3426306”得知果然是ffmpeg的东西，证明成功的调用了库里的方法了。欣慰啊~~

接下来要做的就是学习ffmpeg库里的各种函数的使用方法，以实现自己想要的功能了。