手摸手一步步教你裁剪编译ffmpeg并用于实现安卓端解码。

来源：互联网发布：4g网络优化前景编辑：程序博客网时间：2024/04/29 19:02

编译ffmpeg

请参考： ffmpeg源码编译

使用 ffmpeg.so

如图: 编译成功后会在ffmpeg源码工程目录下的android->arm下生成inlcude（ffmpeg的头文件）和libffmpeg.so。将他俩拷贝到工程的jni目录下。
再写解码的c代码实现decode.c以及交叉编译用的脚本文件Android.mk.和平台配置文件Application.mk。jni目录文件如下（点此下载）：

decode.c文件如下(来源于已故专家雷霄骅博士的博客)，本人在运行到avformat_open_input函数时出现打不开视频文件的错误，于是添加了打印具体错误日志信息的方法，有利排错，详见avformat_open_input打开视频文件错误的解决：

/** * 雷霄骅 Lei Xiaohua * leixiaohua1020@126.com * 中国传媒大学/数字电视技术 * 本程序是安卓平台下最简单的基于FFmpeg的视频解码器。它可以将输入的视频数据解码成YUV像素数据。 */#include <stdio.h>#include <time.h>#include "libavcodec/avcodec.h"#include "libavformat/avformat.h"#include "libswscale/swscale.h"#include "libavutil/log.h"#ifdef ANDROID#include <jni.h>#include <android/log.h>#define LOGE(format, ...)  __android_log_print(ANDROID_LOG_ERROR, "(>_<)", format, ##__VA_ARGS__)#define LOGI(format, ...)  __android_log_print(ANDROID_LOG_INFO,  "(^_^)", format, ##__VA_ARGS__)#else#define LOGE(format, ...)  printf("(>_<) " format "\n", ##__VA_ARGS__)#define LOGI(format, ...)  printf("(^_^) " format "\n", ##__VA_ARGS__)#endif//Output FFmpeg's av_log()void custom_log(void *ptr, int level, const char* fmt, va_list vl) {    FILE *fp = fopen("/storage/emulated/0/av_log.txt", "a+");    if (fp) {        vfprintf(fp, fmt, vl);        fflush(fp);        fclose(fp);    }}JNIEXPORT jint JNICALL Java_com_test_jt_MainActivity_decode(JNIEnv *env,        jobject obj, jstring input_jstr, jstring output_jstr) {    AVFormatContext *pFormatCtx;    int i, videoindex;    AVCodecContext *pCodecCtx;    AVCodec *pCodec;    AVFrame *pFrame, *pFrameYUV;    uint8_t *out_buffer;    AVPacket *packet;    int y_size;    int ret, got_picture;    struct SwsContext *img_convert_ctx;    FILE *fp_yuv;    int frame_cnt;    clock_t time_start, time_finish;    double time_duration = 0.0;    char input_str[500] = { 0 };    char output_str[500] = { 0 };    char info[1000] = { 0 };    sprintf(input_str, "%s", (*env)->GetStringUTFChars(env, input_jstr, NULL));    sprintf(output_str, "%s",            (*env)->GetStringUTFChars(env, output_jstr, NULL));    //FFmpeg av_log() callback    av_log_set_callback(custom_log);    av_register_all();    avformat_network_init();    pFormatCtx = avformat_alloc_context();    int err_code;    char buf[1024];    if ((err_code = avformat_open_input(&pFormatCtx, input_str, NULL, NULL))            != 0) {        av_strerror(err_code, buf, 1024);        LOGE("Couldn't open file %s: %d(%s)", input_str, err_code, buf);        return -1;    }    if (avformat_find_stream_info(pFormatCtx, NULL) < 0) {        LOGE("Couldn't find stream information.\n");        return -1;    }    videoindex = -1;    for (i = 0; i < pFormatCtx->nb_streams; i++)        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {            videoindex = i;            break;        }    if (videoindex == -1) {        LOGE("Couldn't find a video stream.\n");        return -1;    }    pCodecCtx = pFormatCtx->streams[videoindex]->codec;    pCodec = avcodec_find_decoder(pCodecCtx->codec_id);    if (pCodec == NULL) {        LOGE("Couldn't find Codec.\n");        return -1;    }    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0) {        LOGE("Couldn't open codec.\n");        return -1;    }    pFrame = av_frame_alloc();    pFrameYUV = av_frame_alloc();    out_buffer = (unsigned char *) av_malloc(            av_image_get_buffer_size(AV_PIX_FMT_YUV420P, pCodecCtx->width,                    pCodecCtx->height, 1));    av_image_fill_arrays(pFrameYUV->data, pFrameYUV->linesize, out_buffer,            AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height, 1);    packet = (AVPacket *) av_malloc(sizeof(AVPacket));    img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height,            pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height,            AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);    sprintf(info, "[Input     ]%s\n", input_str);    sprintf(info, "%s[Output    ]%s\n", info, output_str);    sprintf(info, "%s[Format    ]%s\n", info, pFormatCtx->iformat->name);    sprintf(info, "%s[Codec     ]%s\n", info, pCodecCtx->codec->name);    sprintf(info, "%s[Resolution]%dx%d\n", info, pCodecCtx->width,            pCodecCtx->height);    fp_yuv = fopen(output_str, "wb+");    if (fp_yuv == NULL) {        printf("Cannot open output file.\n");        return -1;    }    frame_cnt = 0;    time_start = clock();    while (av_read_frame(pFormatCtx, packet) >= 0) {        if (packet->stream_index == videoindex) {            ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture,                    packet);            if (ret < 0) {                LOGE("Decode Error.\n");                return -1;            }            if (got_picture) {                sws_scale(img_convert_ctx,                        (const uint8_t* const *) pFrame->data, pFrame->linesize,                        0, pCodecCtx->height, pFrameYUV->data,                        pFrameYUV->linesize);                y_size = pCodecCtx->width * pCodecCtx->height;                fwrite(pFrameYUV->data[0], 1, y_size, fp_yuv); //Y                fwrite(pFrameYUV->data[1], 1, y_size / 4, fp_yuv); //U                fwrite(pFrameYUV->data[2], 1, y_size / 4, fp_yuv); //V                //Output info                char pictype_str[10] = { 0 };                switch (pFrame->pict_type) {                case AV_PICTURE_TYPE_I:                    sprintf(pictype_str, "I");                    break;                case AV_PICTURE_TYPE_P:                    sprintf(pictype_str, "P");                    break;                case AV_PICTURE_TYPE_B:                    sprintf(pictype_str, "B");                    break;                default:                    sprintf(pictype_str, "Other");                    break;                }                LOGI("Frame Index: %5d. Type:%s", frame_cnt, pictype_str);                frame_cnt++;            }        }        av_free_packet(packet);    }    //flush decoder    //FIX: Flush Frames remained in Codec    while (1) {        ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);        if (ret < 0)            break;        if (!got_picture)            break;        sws_scale(img_convert_ctx, (const uint8_t* const *) pFrame->data,                pFrame->linesize, 0, pCodecCtx->height, pFrameYUV->data,                pFrameYUV->linesize);        int y_size = pCodecCtx->width * pCodecCtx->height;        fwrite(pFrameYUV->data[0], 1, y_size, fp_yuv); //Y        fwrite(pFrameYUV->data[1], 1, y_size / 4, fp_yuv); //U        fwrite(pFrameYUV->data[2], 1, y_size / 4, fp_yuv); //V        //Output info        char pictype_str[10] = { 0 };        switch (pFrame->pict_type) {        case AV_PICTURE_TYPE_I:            sprintf(pictype_str, "I");            break;        case AV_PICTURE_TYPE_P:            sprintf(pictype_str, "P");            break;        case AV_PICTURE_TYPE_B:            sprintf(pictype_str, "B");            break;        default:            sprintf(pictype_str, "Other");            break;        }        LOGI("Frame Index: %5d. Type:%s", frame_cnt, pictype_str);        frame_cnt++;    }    time_finish = clock();    time_duration = (double) (time_finish - time_start);    sprintf(info, "%s[Time      ]%fms\n", info, time_duration);    sprintf(info, "%s[Count     ]%d\n", info, frame_cnt);    sws_freeContext(img_convert_ctx);    fclose(fp_yuv);    av_frame_free(&pFrameYUV);    av_frame_free(&pFrame);    avcodec_close(pCodecCtx);    avformat_close_input(&pFormatCtx);    return 0;}

Android.mk文件内容如下：

LOCAL_PATH := $(call my-dir)# FFmpeg libraryinclude $(CLEAR_VARS)LOCAL_MODULE := ffmpegLOCAL_SRC_FILES := libffmpeg.soinclude $(PREBUILT_SHARED_LIBRARY)# Programinclude $(CLEAR_VARS)LOCAL_MODULE := decodeLOCAL_SRC_FILES :=decode.cLOCAL_C_INCLUDES += $(LOCAL_PATH)/includeLOCAL_LDLIBS := -llog -lzLOCAL_SHARED_LIBRARIES := ffmpeginclude $(BUILD_SHARED_LIBRARY)

编译安卓下使用的lib.so
配置ndk的主目录到path环境变量，然后在终端切换到jni目录下执行ndk-build.cmd。然后在jni同级目录找到libs文件夹，里面有对应平台的.so库文件(libdecode.so和libffmpeg.so)。注意这里生成的libffmpeg.so会比源码编译出来的小十几%，应该是android studio对它进行了压缩。
本来这步和下一步是采用Android studio集成的NDK开发环境一起的，但由于集成NDK的开发环境经常有各种各样的问题，于是我分开来做。建议大家多试试集成NDK去弄，长远来讲可提高开发效率。
使用.so库进行解码。
创建android studio安卓工程，将上一步生成的各平台的so文件放到与java同级的jniLibs目录（自己创建）。

MainActivity文件中调用解码的代码如下。

public class MainActivity extends AppCompatActivity {    static {        System.loadLibrary("ffmpeg");        System.loadLibrary("decode");    }    public native int decode(String inFile, String outFile);    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Button btGetString = (Button) findViewById(R.id.bt_getString);        btGetString.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                String folderurl= Environment.getExternalStorageDirectory().getPath();                String in =folderurl+"/"+ "joy/pingfanzhilu.mkv";                String out =folderurl+"/"+ "joy/pingfanzhilu.yuv" ;                System.out.println("in:" + in + "out" + out);            }        });    }}

请修改需解码的视频源文件和输出yuv文件的路径。如果只需解码一种或几种文件格式，在编译ffmpeg源码时可修改配置脚本裁剪不需要的解码器和解封装器使得libffmpeg.so文件更小。解码后得到的yuv文件可以使用YUV player播放点击下载，设置成原始文件的宽高播放，否则花屏。

项目源码下载

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