一个使用FFmpeg库读取3gp视频的例子-Android中使用FFmpeg媒体库(三)

本文中的代码来自于https://github.com/churnlabs/android-ffmpeg-sample，更多的可以参考这个项目代码。我会在代码中加一些自己的注释。感谢作者churnlabs给我们提供这么好的例子以供我们学习。
在Android的一些系统层应用开发大多数是采用jni的方式调用，另外对于一些比较吃CPU或者处理逻辑比较复杂的程序，也可以考虑使用jni方式来封装。可以提高程序的执行效率。

本文涉及到以下几个方面：
1 将3gp文件push到模拟机器的sdcard中
2 写jni代码，内部调用ffmpeg库的方法，编译jni库
3 loadLibrary生成的库，然后撰写相应的java代码
4 执行程序，并查看最终运行结果。
最终程序的显示效果如下：


1 使用eclipse的DDMS工具，将vid.3pg push到sdcard中

2 撰写相应的jni文件

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/* * Copyright 2011 - Churn Labs, LLC * * 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. */ /* * This is mostly based off of the FFMPEG tutorial: * http://dranger.com/ffmpeg/ * With a few updates to support Android output mechanisms and to update * places where the APIs have shifted. */ #include <jni.h> #include <string.h> #include <stdio.h> #include <android/log.h> #include <android/bitmap.h> //包含ffmpeg库头文件，这些文件都直接方案jni目录下 #include <libavcodec/avcodec.h> #include <libavformat/avformat.h> #include <libswscale/swscale.h> #define LOG_TAG "FFMPEGSample" #define LOGI(...) __android_log_print(ANDROID_LOG_INFO,LOG_TAG,__VA_ARGS__) #define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__) /* Cheat to keep things simple and just use some globals. */ //全局对象 AVFormatContext *pFormatCtx; AVCodecContext *pCodecCtx; AVFrame *pFrame; AVFrame *pFrameRGB; int videoStream; /* * Write a frame worth of video (in pFrame) into the Android bitmap * described by info using the raw pixel buffer. It's a very inefficient * draw routine, but it's easy to read. Relies on the format of the * bitmap being 8bits per color component plus an 8bit alpha channel. */ //定义的静态方法，将某帧AVFrame在Android的Bitmap中绘制 static void fill_bitmap(AndroidBitmapInfo* info, void *pixels, AVFrame *pFrame) { uint8_t *frameLine; int yy; for (yy = 0; yy < info->height; yy++) { uint8_t* line = (uint8_t*)pixels; frameLine = (uint8_t *)pFrame->data[0] + (yy * pFrame->linesize[0]); int xx; for (xx = 0; xx < info->width; xx++) { int out_offset = xx * 4; int in_offset = xx * 3; line[out_offset] = frameLine[in_offset]; line[out_offset+1] = frameLine[in_offset+1]; line[out_offset+2] = frameLine[in_offset+2]; line[out_offset+3] = 0; } pixels = (char*)pixels + info->stride; } } //定义java回调函数，相当与 com.churnlabs中的ffmpegsample中的MainActivity类中的openFile方法。 void Java_com_churnlabs_ffmpegsample_MainActivity_openFile(JNIEnv * env, jobject this) { int ret; int err; int i; AVCodec *pCodec; uint8_t *buffer; int numBytes; //注册所有的函数 av_register_all(); LOGE("Registered formats"); //打开sdcard中的vid.3gp文件 err = av_open_input_file(&pFormatCtx, "file:/sdcard/vid.3gp", NULL, 0, NULL); LOGE("Called open file"); if(err!=0) { LOGE("Couldn't open file"); return; } LOGE("Opened file"); if(av_find_stream_info(pFormatCtx)<0) { LOGE("Unable to get stream info"); return; } videoStream = -1; //定义设置videoStream for (i=0; i<pFormatCtx->nb_streams; i++) { if(pFormatCtx->streams[i]->codec->codec_type==CODEC_TYPE_VIDEO) { videoStream = i; break; } } if(videoStream==-1) { LOGE("Unable to find video stream"); return; } LOGI("Video stream is [%d]", videoStream); //定义编码类型 pCodecCtx=pFormatCtx->streams[videoStream]->codec; //获取解码器 pCodec=avcodec_find_decoder(pCodecCtx->codec_id); if(pCodec==NULL) { LOGE("Unsupported codec"); return; } //使用特定的解码器打开 if(avcodec_open(pCodecCtx, pCodec)<0) { LOGE("Unable to open codec"); return; } //分配帧空间 pFrame=avcodec_alloc_frame(); //分配RGB帧空间 pFrameRGB=avcodec_alloc_frame(); LOGI("Video size is [%d x %d]", pCodecCtx->width, pCodecCtx->height); //获取大小 numBytes=avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height); 分配空间 buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t)); avpicture_fill((AVPicture *)pFrameRGB, buffer, PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height); } //定义java回调函数，相当与 com.churnlabs中的ffmpegsample中的MainActivity类中的drawFrame方法。 void Java_com_churnlabs_ffmpegsample_MainActivity_drawFrame(JNIEnv * env, jobject this, jstring bitmap) { AndroidBitmapInfo info; void* pixels; int ret; int err; int i; int frameFinished = 0; AVPacket packet; static struct SwsContext *img_convert_ctx; int64_t seek_target; if ((ret = AndroidBitmap_getInfo(env, bitmap, &info)) < 0) { LOGE("AndroidBitmap_getInfo() failed ! error=%d", ret); return; } LOGE("Checked on the bitmap"); if ((ret = AndroidBitmap_lockPixels(env, bitmap, &pixels)) < 0) { LOGE("AndroidBitmap_lockPixels() failed ! error=%d", ret); } LOGE("Grabbed the pixels"); i = 0; while((i==0) && (av_read_frame(pFormatCtx, &packet)>=0)) { if(packet.stream_index==videoStream) { avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet); if(frameFinished) { LOGE("packet pts %llu", packet.pts); // This is much different than the tutorial, sws_scale // replaces img_convert, but it's not a complete drop in. // This version keeps the image the same size but swaps to // RGB24 format, which works perfect for PPM output. int target_width = 320; int target_height = 240; img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, target_width, target_height, PIX_FMT_RGB24, SWS_BICUBIC, NULL, NULL, NULL); if(img_convert_ctx == NULL) { LOGE("could not initialize conversion context\n"); return; } sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameRGB->data, pFrameRGB->linesize); // save_frame(pFrameRGB, target_width, target_height, i); fill_bitmap(&info, pixels, pFrameRGB); i = 1; } } av_free_packet(&packet); } AndroidBitmap_unlockPixels(env, bitmap); } //内部调用函数，不对外，用来查找帧 int seek_frame(int tsms) { int64_t frame; frame = av_rescale(tsms,pFormatCtx->streams[videoStream]->time_base.den,pFormatCtx->streams[videoStream]->time_base.num); frame/=1000; if(avformat_seek_file(pFormatCtx,videoStream,0,frame,frame,AVSEEK_FLAG_FRAME)<0) { return 0; } avcodec_flush_buffers(pCodecCtx); return 1; } //定义java回调函数，相当与 com.churnlabs中的ffmpegsample中的MainActivity类中的drawFrameAt方法。 void Java_com_churnlabs_ffmpegsample_MainActivity_drawFrameAt(JNIEnv * env, jobject this, jstring bitmap, jint secs) { AndroidBitmapInfo info; void* pixels; int ret; int err; int i; int frameFinished = 0; AVPacket packet; static struct SwsContext *img_convert_ctx; int64_t seek_target; if ((ret = AndroidBitmap_getInfo(env, bitmap, &info)) < 0) { LOGE("AndroidBitmap_getInfo() failed ! error=%d", ret); return; } LOGE("Checked on the bitmap"); if ((ret = AndroidBitmap_lockPixels(env, bitmap, &pixels)) < 0) { LOGE("AndroidBitmap_lockPixels() failed ! error=%d", ret); } LOGE("Grabbed the pixels"); seek_frame(secs * 1000); i = 0; while ((i== 0) && (av_read_frame(pFormatCtx, &packet)>=0)) { if(packet.stream_index==videoStream) { avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet); if(frameFinished) { // This is much different than the tutorial, sws_scale // replaces img_convert, but it's not a complete drop in. // This version keeps the image the same size but swaps to // RGB24 format, which works perfect for PPM output. int target_width = 320; int target_height = 240; img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, target_width, target_height, PIX_FMT_RGB24, SWS_BICUBIC, NULL, NULL, NULL); if(img_convert_ctx == NULL) { LOGE("could not initialize conversion context\n"); return; } sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameRGB->data, pFrameRGB->linesize); // save_frame(pFrameRGB, target_width, target_height, i); fill_bitmap(&info, pixels, pFrameRGB); i = 1; } } av_free_packet(&packet); } AndroidBitmap_unlockPixels(env, bitmap); }

3 撰写相应的Android.mk文件

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LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_MODULE := ffmpegutils LOCAL_SRC_FILES := native.c LOCAL_C_INCLUDES := $(LOCAL_PATH)/include LOCAL_LDLIBS := -L$(NDK_PLATFORMS_ROOT)/$(TARGET_PLATFORM)/arch-arm/usr/lib -L$(LOCAL_PATH) -lavformat -lavcodec -lavdevice -lavfilter -lavcore -lavutil -lswscale -llog -ljnigraphics -lz -ldl -lgcc include $(BUILD_SHARED_LIBRARY)

这里需要注意一下文件的目录情况，我截图说明一下。

在Android.mk中有意个LOCAL_C_INCLUDES :=$(LOCAL_PATH)/include指明了相应的FFmpeg的头文件路径。故在代码中包含

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#include <libavcodec/avcodec.h> #include <libavformat/avformat.h> #include <libswscale/swscale.h>

就可以。

4 调用ndk-build，生成libffmpegutils.so文件，将这个文件拷贝到/root/develop/android-ndk-r6/platforms/android-8/arch-arm/usr/lib目录，使得我们在下面使用Android AVD2.2的时候，可以加载到这个so文件。

5 撰写相应的Eclipse项目代码，由于在native.c文件中指明了项目的工程名词以及类名词还有函数名词，故我们的项目为com.churnlabs.ffmpegsample下面的MainActivity.java文件

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package com.churnlabs.ffmpegsample; import android.app.Activity; import android.graphics.Bitmap; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.ImageView; public class MainActivity extends Activity { private static native void openFile(); private static native void drawFrame(Bitmap bitmap); private static native void drawFrameAt(Bitmap bitmap, int secs); private Bitmap mBitmap; private int mSecs = 0; static { System.loadLibrary("ffmpegutils"); } /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //setContentView(new VideoView(this)); setContentView(R.layout.main); mBitmap = Bitmap.createBitmap(320, 240, Bitmap.Config.ARGB_8888); openFile(); Button btn = (Button)findViewById(R.id.frame_adv); btn.setOnClickListener(new OnClickListener() { public void onClick(View v) { drawFrame(mBitmap); ImageView i = (ImageView)findViewById(R.id.frame); i.setImageBitmap(mBitmap); } }); Button btn_fwd = (Button)findViewById(R.id.frame_fwd); btn_fwd.setOnClickListener(new OnClickListener() { public void onClick(View v) { mSecs += 5; drawFrameAt(mBitmap, mSecs); ImageView i = (ImageView)findViewById(R.id.frame); i.setImageBitmap(mBitmap); } }); Button btn_back = (Button)findViewById(R.id.frame_back); btn_back.setOnClickListener(new OnClickListener() { public void onClick(View v) { mSecs -= 5; drawFrameAt(mBitmap, mSecs); ImageView i = (ImageView)findViewById(R.id.frame); i.setImageBitmap(mBitmap); } }); } }

6 编译运行即可，最终效果图

7 项目代码下载：

https://github.com/churnlabs/android-ffmpeg-sample/zipball/master

参考：
1 https://github.com/churnlabs/android-ffmpeg-sample
2 http://www.360doc.com/content/10/1216/17/474846_78726683.shtml
3 https://github.com/prajnashi