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• Running ffmpeg as library in android

  4 février 2014, par szakal

  I've got a simple task to do. I need to merge set of pictures into a video using ffmpeg working in android environment.

  After over a week fighting with different tutorials and examples explaining how to run compile ffmpeg I have, let's say, middle success. I've finally compiled ffmpeg for android.

  I followed this example :
  https://github.com/appunite/AndroidFFmpeg
  which worked best for me.

  As a result of building ffmpeg a have following directory structure :

  [Project]/jni/ffmpeg-build/armeabi-v7a/libffmpeg.so
  
  [Project]/jni/ffmpeg-build/armeabi/libffmpeg.so
  
  [Project]/jni/ffmpeg-build/mips/libffmpeg.so
  
  [Project]/jni/ffmpeg-build/x86/libffmpeg.so

  I also followed the ndk examples so I have running c code from java :

  #include 
  
  #include 
  
  #include 
  
  #include 
  
  #include     
  
  #include <android></android>log.h>    
  
  #include 
  
  #include 
  
  
  
  bool initted = false;    
  
  static JavaVM *sVm;
  
  
  
  jstring Java_com_example_hellojni_HelloJni_stringFromJNI(JNIEnv* env, jobject thiz) {
  
  
  
      char **argv;
  
      char *cmd;
  
      int argc;
  
  
  
  //  cmd = "ffmpeg -version";
  
  //  argv = parsedargs(cmd, &amp;argc);
  
  //  ffmpeg(argc, argv);
  
  
  
      return (*env)->NewStringUTF(env, "Hello from JNI !");
  
  
  
  }

  My question is how to run function from ffmpeg from my "hello-jni" c-file. I've read I need to write a wrapper over ffmpeg which my hello-jni is intended to be.

  Here is my Android.mk which probably is importat part to achieve my goal, but honestly I don't understand some lines set in this file. Or simply I don't know how to make things work.

  LOCAL_PATH := $(call my-dir)
  
  
  
  include $(CLEAR_VARS)
  
  LOCAL_MODULE := ffmpeg-prebuilt
  
  LOCAL_SRC_FILES := ffmpeg-build/$(TARGET_ARCH_ABI)/libffmpeg.so
  
  LOCAL_EXPORT_C_INCLUDES := ffmpeg-build/$(TARGET_ARCH_ABI)/include
  
  LOCAL_EXPORT_LDLIBS := ffmpeg-build/$(TARGET_ARCH_ABI)/libffmpeg.so
  
  LOCAL_PRELINK_MODULE := true
  
  include $(PREBUILT_SHARED_LIBRARY)
  
  
  
  
  
  include $(CLEAR_VARS)
  
  LOCAL_ALLOW_UNDEFINED_SYMBOLS=true
  
  LOCAL_MODULE    := hello-jni
  
  LOCAL_SRC_FILES := hello-jni.c
  
  LOCAL_C_INCLUDES := $(LOCAL_PATH)/ffmpeg-build/$(TARGET_ARCH_ABI)/include
  
  LOCAL_SHARED_LIBRARY := ffmpeg-prebuilt
  
  #LOCAL_CFLAGS += -g -Iffmpeg-prebuilt -Ihello-jni -Wno-deprecated-declarations 
  
  #LOCAL_LDLIBS += -llog -lz -landroid ffmpeg-build/$(TARGET_ARCH_ABI)/libffmpeg.so 
  
  
  
  include $(BUILD_SHARED_LIBRARY)

  One more thing. I've found an example how to wrap ffmpeg's main function. It'd be the easiest way to use ffmpeg for me sinse I don't know ffmpeg's api and I hope it's possible to run ffmpeg this way :
  Can FFmpeg be used as a library, instead of a standalone program ?

  To sum up, I think my problems are due to completely lack of c/c++ knowledge at all, especially how to use run any function from .so library.

  I hope someone can help me :).

• Android using JNI without static variables

  21 février 2013, par William Seemann

  I created my own version of Android's MediaMetadataRetriever using the source code for MediaMetadataRetriever.java as the basis. My version uses FFmpeg to retrieve the metadata. This approach works however it relies on static variables in the C code to retain state in between JNI calls. This means I can only use one instance of this class at a time or the state can get corrupted. The two Java functions are defined as follows :

  public class MediaMetadataRetriever
  
  {
  
      static {
  
          System.loadLibrary("metadata_retriever_jni");
  
      }
  
  
  
      public MediaMetadataRetriever() {
  
  
  
      }
  
  
  
      public native void setDataSource(String path) throws IllegalArgumentException;
  
      public native String extractMetadata(String key);

  }

  The corresponding C (JNI) code code is :

  const char *TAG = "Java_com_example_metadataexample_MediaMetadataRetriever";
  
  static AVFormatContext *pFormatCtx = NULL;
  
  
  
  JNIEXPORT void JNICALL
  
  Java_com_example_metadataexample_MediaMetadataRetriever_setDataSource(JNIEnv *env, jclass obj, jstring jpath) {
  
  
  
      if (pFormatCtx) {
  
          avformat_close_input(&pFormatCtx);
  
      }
  
  
  
      char duration[30] = "0";
  
      const char *uri;
  
  
  
      uri = (*env)->GetStringUTFChars(env, jpath, NULL);
  
  
  
      if (avformat_open_input(&pFormatCtx, uri, NULL, NULL) != 0) {
  
          __android_log_write(ANDROID_LOG_INFO, TAG, "Metadata could not be retrieved");
  
          (*env)->ReleaseStringUTFChars(env, jpath, uri);
  
          jniThrowException(env, "java/lang/IllegalArgumentException", NULL);
  
          return;
  
      }
  
  
  
      if (avformat_find_stream_info(pFormatCtx, NULL) < 0) {
  
          __android_log_write(ANDROID_LOG_INFO, TAG, "Metadata could not be retrieved");
  
          avformat_close_input(&pFormatCtx);
  
          (*env)->ReleaseStringUTFChars(env, jpath, uri);
  
          jniThrowException(env, "java/lang/IllegalArgumentException", NULL);
  
          return;
  
      }
  
  
  
      (*env)->ReleaseStringUTFChars(env, jpath, uri);
  
  }
  
  
  
  JNIEXPORT jstring JNICALL
  
  Java_com_example_metadataexample_MediaMetadataRetriever_extractMetadata(JNIEnv *env, jclass obj, jstring jkey) {
  
  
  
      const char *key;
  
      jstring value = NULL;
  
  
  
      key = (*env)->GetStringUTFChars(env, jkey, NULL) ;
  
  
  
      if (!pFormatCtx) {
  
          goto fail;
  
      }
  
  
  
      if (key) {
  
          if (av_dict_get(pFormatCtx->metadata, key, NULL, AV_DICT_IGNORE_SUFFIX)) {
  
              value = (*env)->NewStringUTF(env, av_dict_get(pFormatCtx->metadata, key, NULL, AV_DICT_IGNORE_SUFFIX)->value);
  
          }
  
      }
  
  
  
      fail:
  
      (*env)->ReleaseStringUTFChars(env, jkey, key);
  
  
  
      return value;
  
  }

  Sample usage that outlines my issue would be :

  MediaMetadataRetriever mmr = new MediaMetadataRetriever();
  
  mmr.setDataSource("one.mp3");
  
  
  
  MediaMetadataRetriever mmr2 = new MediaMetadataRetriever();
  
  // This line resets the data source to two.mp3
  
  mmr2.setDataSource("two.mp3");
  
  
  
  // should retrieve the artist from one.mp3 but retrieves it from two.mp3 due to the static
  
  // variable being reset in the previous statement       
  
  String artist = mmr.extractMetadata(MediaMetadataRetriever.ARTIST);

  Can someone explain how I would structure this code so I could use multiple instances of MediaMetadataRetriever without them interfering with one another ? I don't want to switch the code to C++ and I'm fairly certain I don't need to modify MediaMetadataRetriever.java since this code is taken line-for-line from the Android framework (which allows multiple instances, see example below). It appears I need to re-structure the C code but I'm unsure how to retain state across JNI calls without using a static variable. Thanks in advance.

  File file1 = new File(Environment.getExternalStorageDirectory(), "Music/one.mp3");
  
  File file2 = new File(Environment.getExternalStorageDirectory(), "Music/two.mp3");
  
  
  
  android.media.MediaMetadataRetriever mmr = new android.media.MediaMetadataRetriever();
  
  mmr.setDataSource(file1.toString());
  
  
  
  android.media.MediaMetadataRetriever mmr2 = new android.media.MediaMetadataRetriever();
  
  mmr2.setDataSource(file2.toString());
  
  
  
  // Returns the artist of one.mp3, not two.mp3, as expected. This is the expected behavior
  
  // and confirms that multiple instances of MediaMetadataRetriever can be used simultaneously
  
  mmr.extractMetadata(android.media.MediaMetadataRetriever.METADATA_KEY_ARTIST));

• Configure ffmpg for android under Windows system [on hold]

  7 janvier 2014, par Mrityunjoy Mukherjee

  How do I configure ffmpeg for android under Windows system. I have searched a lot . But I have not got the proper way to configure ffmpeg for android under Windows system. Please help on this topic.......