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

原文：http://doandroid.info/?p=497

在续系列文章在32位的Ubuntu 11.04中为Android NDK r6编译FFmpeg0.8.1版-Android中使用FFmpeg媒体库(一)和在Android中通过jni方式使用编译好的FFmpeg库-Android中使用FFmpeg媒体库(二)文章后，本文将根据github中churnlabs的一个开源项目，来深入展开说明如何使用FFmpeg库进行多媒体的开发。
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

/** 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videoStreamfor (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

LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)LOCAL_MODULE := ffmpegutilsLOCAL_SRC_FILES := native.cLOCAL_C_INCLUDES := $(LOCAL_PATH)/includeLOCAL_LDLIBS := -L$(NDK_PLATFORMS_ROOT)/$(TARGET_PLATFORM)/arch-arm/usr/lib -L$(LOCAL_PATH) -lavformat -lavcodec -lavdevice -lavfilter -lavcore -lavutil -lswscale -llog -ljnigraphics -lz -ldl -lgccinclude $(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

#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

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. */@Overridepublic 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

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