android ijkplayer c层分析-初始化

摘要：管协议和编解码，管渲染显示，管理播放器。然后是，这个最后会走到基本上以的初始化内容居多，开头的应该都是。然后是，的网络初始化。这下子与基础协议对应的各项操作算是找到了。终于分析完了，总结起来就是各种初始化，协议的解码器的网络的回调上层的。

本来这个过程我是不大想写初始化的过程，觉得网上已经有不少文章来分析了。但是在前面的整个分析过程中，暴露了自己对一些问题理解还不够透彻，因此有必要做一次。
首先是java层：

private void initPlayer(IjkLibLoader libLoader) {
        loadLibrariesOnce(libLoader);
        initNativeOnce();

        Looper looper;
        if ((looper = Looper.myLooper()) != null) {
            mEventHandler = new EventHandler(this, looper);
        } else if ((looper = Looper.getMainLooper()) != null) {
            mEventHandler = new EventHandler(this, looper);
        } else {
            mEventHandler = null;
        }

        /*
         * Native setup requires a weak reference to our object. It"s easier to
         * create it here than in C++.
         */
        native_setup(new WeakReference(this));
    }

其实就2个事情，一个是loadLibrariesOnce，一个是initNativeOnce。前者的代码就不贴了，就是loadLibrary3个so，分别是ijkffmpeg、ijksdl和ijkplayer。ffmpeg管协议和编解码，sdl管渲染显示，ijkplayer管理播放器。每次调用loadLibrary都会走到每个so的JNI_OnLoad函数，也就是说这3个so的最开始初始化都在JNI_OnLoad这个函数内处理。回头我们再看；后者的initNativeOnce里面实际上走的是native_init。这个对应的是jni的函数IjkMediaPlayer_native_init。在ijkplayer_jni.c中：

static void
IjkMediaPlayer_native_init(JNIEnv *env)
{
    MPTRACE("%s
", __func__);
}

什么都没干，对吧。
回来，看看JNI_OnLoad都干了什么：

JNIEXPORT jint JNI_OnLoad(JavaVM *vm, void *reserved)
{
    JNIEnv* env = NULL;

    g_jvm = vm;
    if ((*vm)->GetEnv(vm, (void**) &env, JNI_VERSION_1_4) != JNI_OK) {
        return -1;
    }
    assert(env != NULL);

    pthread_mutex_init(&g_clazz.mutex, NULL );

    // FindClass returns LocalReference
    IJK_FIND_JAVA_CLASS(env, g_clazz.clazz, JNI_CLASS_IJKPLAYER);
    (*env)->RegisterNatives(env, g_clazz.clazz, g_methods, NELEM(g_methods) );

    ijkmp_global_init();
    ijkmp_global_set_inject_callback(inject_callback);

    FFmpegApi_global_init(env);

    return JNI_VERSION_1_4;
}

前面都是通用的一些做法，主要是注册函数表，用来在java层能够调用c层的函数。然后是ijkmp_global_init，这个最后会走到ffp_global_init：

void ffp_global_init()
{
    if (g_ffmpeg_global_inited)
        return;

    /* register all codecs, demux and protocols */
    avcodec_register_all();
#if CONFIG_AVDEVICE
    avdevice_register_all();
#endif
#if CONFIG_AVFILTER
    avfilter_register_all();
#endif
    av_register_all();

    ijkav_register_all();

    avformat_network_init();

    av_lockmgr_register(lockmgr);
    av_log_set_callback(ffp_log_callback_brief);

    av_init_packet(&flush_pkt);
    flush_pkt.data = (uint8_t *)&flush_pkt;

    g_ffmpeg_global_inited = true;
}

基本上以ffmpeg的初始化内容居多，av开头的应该都是。注册解码器，然后协议的注册。我们看ijkav_register_all：

void ijkav_register_all(void)
{
    static int initialized;

    if (initialized)
        return;
    initialized = 1;

    av_register_all();

    /* protocols */
    av_log(NULL, AV_LOG_INFO, "===== custom modules begin =====
");
#ifdef __ANDROID__
    IJK_REGISTER_PROTOCOL(ijkmediadatasource);
#endif
    IJK_REGISTER_PROTOCOL(async);
    IJK_REGISTER_PROTOCOL(ijklongurl);
    IJK_REGISTER_PROTOCOL(ijktcphook);
    IJK_REGISTER_PROTOCOL(ijkhttphook);
    IJK_REGISTER_PROTOCOL(ijksegment);
    /* demuxers */
    IJK_REGISTER_DEMUXER(ijklivehook);
    av_log(NULL, AV_LOG_INFO, "===== custom modules end =====
");
}

基本上都是为了支持网络传输的协议注册。然后是avformat_network_init，ffmpeg的网络初始化。最后到达ff_network_init，里面就是个WSAStartup。
回来看这么多协议的注册，先看下这个宏：

#define IJK_REGISTER_PROTOCOL(x)                                        
    {                                                                   
        extern URLProtocol ijkimp_ff_##x##_protocol;                        
        int ijkav_register_##x##_protocol(URLProtocol *protocol, int protocol_size);
        ijkav_register_##x##_protocol(&ijkimp_ff_##x##_protocol, sizeof(URLProtocol));  
    }

URLProtocol结构是个关键。那么这个结构的填充靠什么呢？看宏的调用，找到extern后面的部分，搜索下，原来在不少文件里都有，例如ijkurlhook.c文件中：

URLProtocol ijkimp_ff_ijktcphook_protocol = {
    .name                = "ijktcphook",
    .url_open2           = ijktcphook_open,
    .url_read            = ijkurlhook_read,
    .url_write           = ijkurlhook_write,
    .url_close           = ijkurlhook_close,
    .priv_data_size      = sizeof(Context),
    .priv_data_class     = &ijktcphook_context_class,
};

这里已经规定了打开和写入关闭等的函数。这下子与基础协议对应的各项操作算是找到了。我们来看看不一样的live的处理：

#define IJK_REGISTER_DEMUXER(x)                                         
    {                                                                   
        extern AVInputFormat ijkff_##x##_demuxer;                       
        ijkav_register_input_format(&ijkff_##x##_demuxer);              
    }

然后会定位到ijklivehook.c文件中的

AVInputFormat ijkff_ijklivehook_demuxer = {
    .name           = "ijklivehook",
    .long_name      = "Live Hook Controller",
    .flags          = AVFMT_NOFILE | AVFMT_TS_DISCONT,
    .priv_data_size = sizeof(Context),
    .read_probe     = ijklivehook_probe,
    .read_header2   = ijklivehook_read_header,
    .read_packet    = ijklivehook_read_packet,
    .read_close     = ijklivehook_read_close,
    .priv_class     = &ijklivehook_class,
};

往下看，以ijklivehook_read_header为例，可以看到内部有url的判断，区分rtmp和rtsp，这下子清楚了吧。
简单总结一下，就是通过URLProtocol这个结构来规范化所有的协议，名称和操作函数都在这里定义。
回到ffp_global_init，下面进行到了av_init_packet。这里插一下一个数据结构AVPacket。这个是存储压缩编码数据相关信息的结构体。

typedef struct AVPacket {
    /**
     * A reference to the reference-counted buffer where the packet data is
     * stored.
     * May be NULL, then the packet data is not reference-counted.
     */
    AVBufferRef *buf;
    /**
     * Presentation timestamp in AVStream->time_base units; the time at which
     * the decompressed packet will be presented to the user.
     * Can be AV_NOPTS_VALUE if it is not stored in the file.
     * pts MUST be larger or equal to dts as presentation cannot happen before
     * decompression, unless one wants to view hex dumps. Some formats misuse
     * the terms dts and pts/cts to mean something different. Such timestamps
     * must be converted to true pts/dts before they are stored in AVPacket.
     */
    int64_t pts;
    /**
     * Decompression timestamp in AVStream->time_base units; the time at which
     * the packet is decompressed.
     * Can be AV_NOPTS_VALUE if it is not stored in the file.
     */
    int64_t dts;
    uint8_t *data;
    int   size;
    int   stream_index;
    /**
     * A combination of AV_PKT_FLAG values
     */
    int   flags;
    /**
     * Additional packet data that can be provided by the container.
     * Packet can contain several types of side information.
     */
    AVPacketSideData *side_data;
    int side_data_elems;

    /**
     * Duration of this packet in AVStream->time_base units, 0 if unknown.
     * Equals next_pts - this_pts in presentation order.
     */
    int64_t duration;

    int64_t pos;                            ///< byte position in stream, -1 if unknown

#if FF_API_CONVERGENCE_DURATION
    /**
     * @deprecated Same as the duration field, but as int64_t. This was required
     * for Matroska subtitles, whose duration values could overflow when the
     * duration field was still an int.
     */
    attribute_deprecated
    int64_t convergence_duration;
#endif
} AVPacket;

看到了什么吗？pts,dts,data。显示时间戳，解码时间戳，数据。av_init_packet就是个简单填充，不贴代码了。回到JNI_OnLoad，然后进行的是ijkmp_global_set_inject_callback。
设置了一个回调，那么看看具体回调的约定吧：

static int
inject_callback(void *opaque, int what, void *data, size_t data_size)
{
    JNIEnv     *env     = NULL;
    jobject     jbundle = NULL;
    int         ret     = -1;
    SDL_JNI_SetupThreadEnv(&env);

    jobject weak_thiz = (jobject) opaque;
    if (weak_thiz == NULL )
        goto fail;
    switch (what) {
        case AVAPP_CTRL_WILL_HTTP_OPEN:
        case AVAPP_CTRL_WILL_LIVE_OPEN:
        case AVAPP_CTRL_WILL_CONCAT_SEGMENT_OPEN: {
            AVAppIOControl *real_data = (AVAppIOControl *)data;
            real_data->is_handled = 0;

            jbundle = J4AC_Bundle__Bundle__catchAll(env);
            if (!jbundle) {
                ALOGE("%s: J4AC_Bundle__Bundle__catchAll failed for case %d
", __func__, what);
                goto fail;
            }
            J4AC_Bundle__putString__withCString__catchAll(env, jbundle, "url", real_data->url);
            J4AC_Bundle__putInt__withCString__catchAll(env, jbundle, "segment_index", real_data->segment_index);
            J4AC_Bundle__putInt__withCString__catchAll(env, jbundle, "retry_counter", real_data->retry_counter);
            real_data->is_handled = J4AC_IjkMediaPlayer__onNativeInvoke(env, weak_thiz, what, jbundle);
            if (J4A_ExceptionCheck__catchAll(env)) {
                goto fail;
            }

            J4AC_Bundle__getString__withCString__asCBuffer(env, jbundle, "url", real_data->url, sizeof(real_data->url));
            if (J4A_ExceptionCheck__catchAll(env)) {
                goto fail;
            }
            ret = 0;
            break;
        }
        case AVAPP_EVENT_WILL_HTTP_OPEN:
        case AVAPP_EVENT_DID_HTTP_OPEN:
        case AVAPP_EVENT_WILL_HTTP_SEEK:
        case AVAPP_EVENT_DID_HTTP_SEEK: {
            AVAppHttpEvent *real_data = (AVAppHttpEvent *) data;
            jbundle = J4AC_Bundle__Bundle__catchAll(env);
            if (!jbundle) {
                ALOGE("%s: J4AC_Bundle__Bundle__catchAll failed for case %d
", __func__, what);
                goto fail;
            }
            J4AC_Bundle__putString__withCString__catchAll(env, jbundle, "url", real_data->url);
            J4AC_Bundle__putLong__withCString__catchAll(env, jbundle, "offset", real_data->offset);
            J4AC_Bundle__putInt__withCString__catchAll(env, jbundle, "error", real_data->error);
            J4AC_Bundle__putInt__withCString__catchAll(env, jbundle, "http_code", real_data->http_code);
            J4AC_IjkMediaPlayer__onNativeInvoke(env, weak_thiz, what, jbundle);
            if (J4A_ExceptionCheck__catchAll(env))
                goto fail;
            ret = 0;
            break;
        }
        case AVAPP_CTRL_DID_TCP_OPEN:
        case AVAPP_CTRL_WILL_TCP_OPEN: {
            AVAppTcpIOControl *real_data = (AVAppTcpIOControl *)data;
            jbundle = J4AC_Bundle__Bundle__catchAll(env);
            if (!jbundle) {
                ALOGE("%s: J4AC_Bundle__Bundle__catchAll failed for case %d
", __func__, what);
                goto fail;
            }
            J4AC_Bundle__putInt__withCString__catchAll(env, jbundle, "error", real_data->error);
            J4AC_Bundle__putInt__withCString__catchAll(env, jbundle, "family", real_data->family);
            J4AC_Bundle__putString__withCString__catchAll(env, jbundle, "ip", real_data->ip);
            J4AC_Bundle__putInt__withCString__catchAll(env, jbundle, "port", real_data->port);
            J4AC_Bundle__putInt__withCString__catchAll(env, jbundle, "fd", real_data->fd);
            J4AC_IjkMediaPlayer__onNativeInvoke(env, weak_thiz, what, jbundle);
            if (J4A_ExceptionCheck__catchAll(env))
                goto fail;
            ret = 0;
            break;
        }
        default: {
            ret = 0;
        }
    }
fail:
    SDL_JNI_DeleteLocalRefP(env, &jbundle);
    return ret;
}

简单找个函数看下：J4AC_IjkMediaPlayer__onNativeInvoke，在java层里找到了定义：

private OnNativeInvokeListener mOnNativeInvokeListener;
    public void setOnNativeInvokeListener(OnNativeInvokeListener listener) {
        mOnNativeInvokeListener = listener;
    }

    public interface OnNativeInvokeListener {

        int CTRL_WILL_TCP_OPEN = 0x20001;               // NO ARGS
        int CTRL_DID_TCP_OPEN = 0x20002;                // ARG_ERROR, ARG_FAMILIY, ARG_IP, ARG_PORT, ARG_FD

        int CTRL_WILL_HTTP_OPEN = 0x20003;              // ARG_URL, ARG_SEGMENT_INDEX, ARG_RETRY_COUNTER
        int CTRL_WILL_LIVE_OPEN = 0x20005;              // ARG_URL, ARG_RETRY_COUNTER
        int CTRL_WILL_CONCAT_RESOLVE_SEGMENT = 0x20007; // ARG_URL, ARG_SEGMENT_INDEX, ARG_RETRY_COUNTER

        int EVENT_WILL_HTTP_OPEN = 0x1;                 // ARG_URL
        int EVENT_DID_HTTP_OPEN = 0x2;                  // ARG_URL, ARG_ERROR, ARG_HTTP_CODE
        int EVENT_WILL_HTTP_SEEK = 0x3;                 // ARG_URL, ARG_OFFSET
        int EVENT_DID_HTTP_SEEK = 0x4;                  // ARG_URL, ARG_OFFSET, ARG_ERROR, ARG_HTTP_CODE

        String ARG_URL = "url";
        String ARG_SEGMENT_INDEX = "segment_index";
        String ARG_RETRY_COUNTER = "retry_counter";

        String ARG_ERROR = "error";
        String ARG_FAMILIY = "family";
        String ARG_IP = "ip";
        String ARG_PORT = "port";
        String ARG_FD = "fd";

        String ARG_OFFSET = "offset";
        String ARG_HTTP_CODE = "http_code";

        /*
         * @return true if invoke is handled
         * @throws Exception on any error
         */
        boolean onNativeInvoke(int what, Bundle args);
    }

    @CalledByNative
    private static boolean onNativeInvoke(Object weakThiz, int what, Bundle args) {
        DebugLog.ifmt(TAG, "onNativeInvoke %d", what);
        if (weakThiz == null || !(weakThiz instanceof WeakReference))
            throw new IllegalStateException(".onNativeInvoke()");

        @SuppressWarnings("unchecked")
        WeakReference weakPlayer = (WeakReference) weakThiz;
        IjkMediaPlayer player = weakPlayer.get();
        if (player == null)
            throw new IllegalStateException(".onNativeInvoke()");

        OnNativeInvokeListener listener = player.mOnNativeInvokeListener;
        if (listener != null && listener.onNativeInvoke(what, args))
            return true;

        switch (what) {
            case OnNativeInvokeListener.CTRL_WILL_CONCAT_RESOLVE_SEGMENT: {
                OnControlMessageListener onControlMessageListener = player.mOnControlMessageListener;
                if (onControlMessageListener == null)
                    return false;

                int segmentIndex = args.getInt(OnNativeInvokeListener.ARG_SEGMENT_INDEX, -1);
                if (segmentIndex < 0)
                    throw new InvalidParameterException("onNativeInvoke(invalid segment index)");

                String newUrl = onControlMessageListener.onControlResolveSegmentUrl(segmentIndex);
                if (newUrl == null)
                    throw new RuntimeException(new IOException("onNativeInvoke() = "));

                args.putString(OnNativeInvokeListener.ARG_URL, newUrl);
                return true;
            }
            default:
                return false;
        }
    }

那么可以确定，这里是注册的回调，以便通知java层。好吧，回来继续JNI_OnLoad，就差FFmpegApi_global_init了：

#define JNI_CLASS_FFMPEG_API "tv/danmaku/ijk/media/player/ffmpeg/FFmpegApi"
......
int FFmpegApi_global_init(JNIEnv *env)
{
    int ret = 0;

    IJK_FIND_JAVA_CLASS(env, g_clazz.clazz, JNI_CLASS_FFMPEG_API);
    (*env)->RegisterNatives(env, g_clazz.clazz, g_methods, NELEM(g_methods));

    return ret;
}

按照定义，找到这个类，只有一句话：

public class FFmpegApi {
    public static native String av_base64_encode(byte in[]);
}

其实就是个base64的解码，指向ffmpeg的c函数，这里进行了注册。
终于分析完了，总结起来就是各种初始化，协议的、解码器的、网络的、回调上层的。