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

超、凢脫俗 2022-06-18 06:21 186阅读 0赞

原文：[http://doandroid.info/?p=497][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)][32_Ubuntu 11.04_Android NDK r6_FFmpeg0.8.1_-Android_FFmpeg]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)][Android_jni_FFmpeg_-Android_FFmpeg]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：  
[![Screenshot][]][Screenshot 1]  
  
1 使用eclipse的DDMS工具，将vid.3pg push到sdcard中  
[![Screenshot-1][]][Screenshot-1 1]  
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

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。  
[![Screenshot-2][]][Screenshot-2 1]

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. */
        @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  
[![Screenshot][]][Screenshot 1]

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

[http_doandroid.info_p_497]: http://doandroid.info/?p=497
[32_Ubuntu 11.04_Android NDK r6_FFmpeg0.8.1_-Android_FFmpeg]: http://doandroid.info/?p=465
[Android_jni_FFmpeg_-Android_FFmpeg]: http://doandroid.info/?p=471
[Screenshot]: http://doandroid.info/wp-content/uploads/2011/10/Screenshot3-300x211.png
[Screenshot 1]: http://doandroid.info/wp-content/uploads/2011/10/Screenshot3.png
[Screenshot-1]: http://doandroid.info/wp-content/uploads/2011/10/Screenshot-12-300x113.png
[Screenshot-1 1]: http://doandroid.info/wp-content/uploads/2011/10/Screenshot-12.png
[Screenshot-2]: http://doandroid.info/wp-content/uploads/2011/10/Screenshot-22-300x282.png
[Screenshot-2 1]: http://doandroid.info/wp-content/uploads/2011/10/Screenshot-22.png