How to Build Android Applications Based on FFmpeg by An Example

This is a follow up post of the previous blog How to Build FFmpeg for Android.  You can read the previous tutorial first, or refer back to it when you feel necessary.

This blog covers how to build a simple Android app based on FFmpeg library. The app will detect the input video file’s resolution and codec information through interface provided by FFmpeg.

Blow is a screenshot of the app,

Figure 1. Screen shot of the sample android app based on FFmpeg

0. Create a new Android Project FFmpegTest.

When you’re asked to select targeted platform, select 2.2 as it’s the platform used in previous blog. But you’re free to change it.

Also create a folder named jni under the root directory “FFmpegTest” of this project.

1. Download the ffmpeg Source Code and Extract it to jni Folder

Follow the previous blog How to Build FFmpeg for Android to build the library.

2. Write the Native Code that use FFmpeg’s libavcodec library.

You can copy and paste the code below and save it as ffmpeg-test-jni.c under FFmpegTest/jni/ directory. Note that the code below is not completed, you can download the entire code at the end of the post.

/*for android logs*/
#define LOG_TAG "FFmpegTest"
#define LOG_LEVEL 10
#define LOGI(level, ...) if (level <= LOG_LEVEL) {__android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__);}
#define LOGE(level, ...) if (level <= LOG_LEVEL) {__android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__);}
char *gFileName;      //the file name of the video
AVFormatContext *gFormatCtx;
int gVideoStreamIndex;    //video stream index
AVCodecContext *gVideoCodecCtx;
static void get_video_info(char *prFilename);
static void get_video_info(char *prFilename) {
    AVCodec *lVideoCodec;
    int lError;
    /*register the codec*/
    extern AVCodec ff_h264_decoder;
    avcodec_register(&ff_h264_decoder);
    /*register demux*/
    extern AVInputFormat ff_mov_demuxer;
    av_register_input_format(&ff_mov_demuxer);
    /*register the protocol*/
    extern URLProtocol ff_file_protocol;
    av_register_protocol2(&ff_file_protocol, sizeof(ff_file_protocol));
    /*open the video file*/
    if ((lError = av_open_input_file(&gFormatCtx, gFileName, NULL, 0, NULL)) !=0 ) {
        LOGE(1, "Error open video file: %d", lError);
        return;    //open file failed
    }
    /*retrieve stream information*/
    if ((lError = av_find_stream_info(gFormatCtx)) < 0) {
        LOGE(1, "Error find stream information: %d", lError);
        return;
    }
    /*find the video stream and its decoder*/
    gVideoStreamIndex = av_find_best_stream(gFormatCtx, AVMEDIA_TYPE_VIDEO, -1, -1, &lVideoCodec, 0);
    if (gVideoStreamIndex == AVERROR_STREAM_NOT_FOUND) {
        LOGE(1, "Error: cannot find a video stream");
        return;
    } else {
        LOGI(10, "video codec: %s", lVideoCodec->name);
    }
    if (gVideoStreamIndex == AVERROR_DECODER_NOT_FOUND) {
        LOGE(1, "Error: video stream found, but no decoder is found!");
        return;
    }
    /*open the codec*/
    gVideoCodecCtx = gFormatCtx->streams[gVideoStreamIndex]->codec;
    LOGI(10, "open codec: (%d, %d)", gVideoCodecCtx->height, gVideoCodecCtx->width);
    if (avcodec_open(gVideoCodecCtx, lVideoCodec) < 0) {
        LOGE(1, "Error: cannot open the video codec!");
        return;
    }
}
JNIEXPORT void JNICALL Java_roman10_ffmpegTest_VideoBrowser_naInit(JNIEnv *pEnv, jobject pObj, jstring pFileName) {
    int l_mbH, l_mbW;
    /*get the video file name*/
    gFileName = (char *)(*pEnv)->GetStringUTFChars(pEnv, pFileName, NULL);
    if (gFileName == NULL) {
        LOGE(1, "Error: cannot get the video file name!");
        return;
    }
    LOGI(10, "video file name is %s", gFileName);
    get_video_info(gFileName);
}
JNIEXPORT jstring JNICALL Java_roman10_ffmpegTest_VideoBrowser_naGetVideoCodecName(JNIEnv *pEnv, jobject pObj) {
    char* lCodecName = gVideoCodecCtx->codec->name;
    return (*pEnv)->NewStringUTF(pEnv, lCodecName);
}

If you’re not familiar with Java JNI, you may need to read about JNI first in order to understand the code. But this is not the focus of this tutorial hence not covered.

3. Build the Native Code.

Create a file named Android.mk under jni directory and copy paste the content below,

LOCAL_PATH := $(call my-dir)

#declare the prebuilt library
include $(CLEAR_VARS)
LOCAL_MODULE := ffmpeg-prebuilt
LOCAL_SRC_FILES := ffmpeg-0.8/android/armv7-a/libffmpeg.so
LOCAL_EXPORT_C_INCLUDES := ffmpeg-0.8/android/armv7-a/include
LOCAL_EXPORT_LDLIBS := ffmpeg-0.8/android/armv7-a/libffmpeg.so
LOCAL_PRELINK_MODULE := true
include $(PREBUILT_SHARED_LIBRARY)

#the ffmpeg-test-jni library
include $(CLEAR_VARS)
LOCAL_ALLOW_UNDEFINED_SYMBOLS=false
LOCAL_MODULE := ffmpeg-test-jni
LOCAL_SRC_FILES := ffmpeg-test-jni.c
LOCAL_C_INCLUDES := $(LOCAL_PATH)/ffmpeg-0.8/android/armv7-a/include
LOCAL_SHARED_LIBRARY := ffmpeg-prebuilt
LOCAL_LDLIBS    := -llog -ljnigraphics -lz -lm $(LOCAL_PATH)/ffmpeg-0.8/android/armv7-a/libffmpeg.so
include $(BUILD_SHARED_LIBRARY)

Create another file named Application.mk under jni directory and copy paste the content below,

# The ARMv7 is significanly faster due to the use of the hardware FPU
APP_ABI := armeabi-v7a
APP_PLATFORM := android-8

For more information about what Android.mk and Application.mk do, you can refer to the documentation comes with android NDK.

Your folder structure should be something like below after you finish all steps above,

Figure 2. Folder structure of project FFmpegTest and jni

4. Call the Native Code from FFmpegTest Java Code.

You’ll need to load the libraries and declare the jni functions. The code below is extracted from the app source code, which is provided for download at the end of this tutorial.

/*this part communicates with native code through jni (java native interface)*/
    //load the native library
    static {
        System.loadLibrary("ffmpeg");
        System.loadLibrary("ffmpeg-test-jni");
    }
    //declare the jni functions
    private static native void naInit(String _videoFileName);
    private static native int[] naGetVideoResolution();
    private static native String naGetVideoCodecName();
    private static native String naGetVideoFormatName();
    private static native void naClose();

    private void showVideoInfo(final File _file) {
        String videoFilename = _file.getAbsolutePath();
        naInit(videoFilename);
        int[] prVideoRes = naGetVideoResolution();
        String prVideoCodecName = naGetVideoCodecName();
        String prVideoFormatName = naGetVideoFormatName();
        naClose();
        String displayText = "Video: " + videoFilename + "
";
        displayText += "Video Resolution: " + prVideoRes[0] + "x" + prVideoRes[1] + "
";
        displayText += "Video Codec: " + prVideoCodecName + "
";
        displayText += "Video Format: " + prVideoFormatName + "
";
        text_titlebar_text.setText(displayText);
    }

5. You can Download the Entire Source Code from here.

Note: the code is tested on Ubuntu 10.04 and Android ndk-5b, but it should work on other platforms (except for Windows, which I’m not sure about.)