0. 輔導四簡介：多媒體播放器

🤩：謝謝你們，謝謝我的堅持，都到輔導四了，咱們都是吃飽了撐著的哥們，
路人甲👩?🎤：誰跟你是哥們？姐手抖進來這，
😃：FreeDesktop 網主說著是個多媒體播放器，準備好網址沒有？放電影啦！

🏗? 1. Common Module 共用倉庫

對比了輔導三和輔導四，有些檔案是共通的，不要再費時費力，又抄又翻，手指都打疼了，直接來個 common module —— 大家一起分享，

File => New => New Module:
new
Android => Module name: common
lib

??，改 common 的 gradle

打開 common 的 gradle：
gradle

在 dependencies 內：

    api "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
    api "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
    api 'androidx.core:core-ktx:1.3.2'
    api 'androidx.appcompat:appcompat:1.2.0'
    
    // test
    api 'junit:junit:4.13.1'
    api 'androidx.test.ext:junit:1.1.2'
    api 'androidx.test.espresso:espresso-core:3.3.0'

將所有的開頭改成 api ，sync，😋：看！想都不用想，懶人最愛！
…

🕵?，加自己的捷徑包

在 Java 加個 helper 的 package 包裹，把 Log，Toast 的私貨塞進去，
helper
LogHelper:

const val TAG = "MTAG"
fun lgd(s:String) = Log.d(TAG, s)
fun lgi(s:String) = Log.i(TAG, s)
fun lge(s:String) = Log.e(TAG, s)
fun lgw(s:String) = Log.w(TAG, s)
fun lgv(s:String) = Log.v(TAG, s)

ToastHelper:

// Toast: len: 0-short, 1-long
fun msg(context: Context, s: String, len: Int) =
    if (len > 0) Toast.makeText(context, s, LENGTH_LONG).show()
    else Toast.makeText(context, s, LENGTH_SHORT).show()

…

📦，GStreamer package 包裹

加 package 包裹：common => java => New => Package
newPkg
main
選 main\java ，
free
繼續抄：

copy
讓 assets 和 GStreamer.java 駐新家，
…

《??》改輔導一

Gradle：跳到 dependencies
change
😋：換成一行的，夠短了吧? Sync，
Tutorial1.kt：看看私貨能用否？

    public override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        try {
            GStreamer.init(this)
        } catch (e: Exception) {
            msg(this, e.message.toString(), 1)
            finish()
            return
        }
        setContentView(R.layout.main)
        val tv = findViewById<View>(R.id.textview_info) as TextView
        tv.text = nativeGetGStreamerInfo() + " !"
    }

把 Toast() 改成 msg() ，
再將 GStreamer 和 assets 刪掉，
del
import 回來，

import
跑一次，😁：一樣，
install
Android Studio 自動把 GStreamer 和 assets 裝回去了，以后裝在新專案，也可以這樣操作，

…

《??》改輔導二的

Gradle：在 dependencies 縮水， sync，
Tutorial2.kt：將 lgd， lgi 的 import 刪掉，再 import 一次，
跑步前進…一切正常，
…

《??》改輔導三

Gradle：在 dependencies 縮水， sync，
Tutorial3.kt：將 lgd， lgi 的 import 刪掉，再 import 一次，
🉑 輔導三，輔導四和輔導五共用一個 GStreamerSurfaceView，因此，這個可以搬到 common 里面去：

刪掉輔導三里面的 GStreamerSurfaceView，
在 res/layout/main.xml ：

    <你的路徑.common.ui.GStreamerSurfaceView
        android:id="@+id/surface_video"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical|center_horizontal" />

抬頭換成新的地址，象我就是

com.homan.huang.common.ui.GStreamerSurfaceView

跑啊…正常，

?? 2. 輔導四轉 Kotlin

【??】Gradle 和 main.xml

Gradle：在 dependencies 縮水， sync，👌
main.xml: 轉 “你的路徑.common.ui.GStreamerSurfaceView”

到 Tutorial4 ，跑起來呦，沒問題，
…

【??】Tutorial4.Java 轉 Kotlin

老樣子，Ctrl+Alt+Shift+k，Yes：
有三處爆紅：

Date(pos) 改為 Date(pos.toLong())
Date(duration）改為 Date(duration.toLong())
照舊給 nativeClassInit() 加 @JvmStatic

再跑起來，沒事，
film
音響和畫面看起來都不錯，

3. 分析 Turtorial4

class Tutorial4 : Activity(), SurfaceHolder.Callback, OnSeekBarChangeListener {

🤔（一看開頭就知道好多仔啊！）：你哪來的？下蛋啊？
🐔？？？🐤🐥🐣

🐾 JNI 引數

    // JNI
    private external fun nativeInit() // Initialize native code, build pipeline, etc
    private external fun nativeFinalize() // Destroy pipeline and shutdown native code
    private external fun nativeSetUri(uri: String?) // Set the URI of the media to play
    private external fun nativePlay() // Set pipeline to PLAYING
    private external fun nativeSetPosition(milliseconds: Int) // Seek to the indicated position, in milliseconds
    private external fun nativePause() // Set pipeline to PAUSED
    private external fun nativeSurfaceInit(surface: Any) // A new surface is available
    private external fun nativeSurfaceFinalize() // Surface about to be destroyed
    private val native_custom_data // Native code will use this to keep private data
            : Long = 0
    private var is_playing_desired // Whether the user asked to go to PLAYING
            = false
    private var position // Current position, reported by native code
            = 0
    private var duration // Current clip duration, reported by native code
            = 0
    private var is_local_media // Whether this clip is stored locally or is being streamed
            = false
    private var desired_position // Position where the users wants to seek to
            = 0
    private var mediaUri // URI of the clip being played
            : String? = null
    private val defaultMediaUri = "https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.ogv"

有流量當然有 URI
放電影還要有 poistion 位置顯示
播過了多長時間 duration
下面還有資源判斷是當地的還是網上的 is_local_media
用戶選項有一個：跳檔，desired_position
下一個 mediaUri，網源
最后一個 defaultMediaUri

📺 UI 觸屏引數

    // UI
    val play:ImageButton by lazy { findViewById(R.id.button_play) }
    val pause:ImageButton by lazy { findViewById(R.id.button_stop) }
    val sb:SeekBar by lazy { findViewById(R.id.seek_bar) }
    val msgTV:TextView by lazy { findViewById(R.id.textview_message) }
    val timeTV:TextView by lazy { findViewById(R.id.textview_time) }
    val gsv:GStreamerSurfaceView by lazy { findViewById(R.id.surface_video) }

player
…

🔨 onCreate()

        // 搜索棍
        sb.setOnSeekBarChangeListener(this)

搜索棍 seek_bar

        // Retrieve our previous state, or initialize it to default values
        if (savedInstanceState != null) {
            is_playing_desired = savedInstanceState.getBoolean("playing")
            position = savedInstanceState.getInt("position")
            duration = savedInstanceState.getInt("duration")
            mediaUri = savedInstanceState.getString("mediaUri")
            lgi("GStreamer--Activity created with saved state:")
        } else {
            is_playing_desired = false
            duration = 0
            position = duration
            mediaUri = defaultMediaUri
            lgi("GStreamer--Activity created with no saved state:")
        }

檢查 onRestart() 或 onStart() 回呼的記憶，🙄：防止機器癡呆，onSaveInstanceState() 保持播放器的資料，

    override fun onSaveInstanceState(outState: Bundle) {
        lgd("GStreamer--Saving state, playing:" + is_playing_desired + " position:" + position +
                " duration: " + duration + " uri: " + mediaUri)
        outState.putBoolean("playing", is_playing_desired)
        outState.putInt("position", position)
        outState.putInt("duration", duration)
        outState.putString("mediaUri", mediaUri)
    }

接著，

is_local_media = false

默認使用網路流量，
…

🛵onGStreamerInitialized()

    private fun onGStreamerInitialized() {
        ...
        // Restore previous playing state
        setMediaUri()
        nativeSetPosition(position)
        ...
    }

多了兩行，

setMediaUri():

    private fun setMediaUri() {
        nativeSetUri(mediaUri)
        is_local_media = mediaUri!!.startsWith("file://")
    }

通知 C 網址，

…

📥 Implementation 插入的方程，

surfaceChanged(), surfaceCreated(), surfaceDestroyed() 你們都知道了，

📲 onMediaSizeChanged()：

    private fun onMediaSizeChanged(width: Int, height: Int) {
        lgi("GStreamer--Media size changed to " + width + "x" + height)
        gsv.media_width = width
        gsv.media_height = height
        runOnUiThread { gsv.requestLayout() }
    }

平放看看：
hor
鎖死了，

        gsv.media_width = height
        gsv.media_height = width

長寬掉轉，成了：
long
👨?🔧：這個播放器沒法用，還是改回來吧，還有這些按鈕都是非人類的，誰會擺在中間啊？
…

📏 播放搜索棍

🧙?♂?：這個不及我的棒棒，只能提放推拉，

    // The Seek Bar thumb has moved, either because the user dragged it or we have called setProgress()
    override fun onProgressChanged(sb: SeekBar, progress: Int, fromUser: Boolean) {
        if (fromUser == false) return
        desired_position = progress
        // If this is a local file, allow scrub seeking, this is, seek as soon as the slider is moved.
        if (is_local_media) nativeSetPosition(desired_position)
        updateTimeWidget()
    }

    // The user started dragging the Seek Bar thumb
    override fun onStartTrackingTouch(sb: SeekBar) {
        nativePause()
    }

    // The user released the Seek Bar thumb
    override fun onStopTrackingTouch(sb: SeekBar) {
        // If this is a remote file, scrub seeking is probably not going to work smoothly enough.
        // Therefore, perform only the seek when the slider is released.
        if (!is_local_media) nativeSetPosition(desired_position)
        if (is_playing_desired) nativePlay()
    }

onProgressChanged() 跳動播放地方
onStartTrackingTouch() 抓動感應
onStopTrackingTouch() 放手之后

?4. 分析 tutorial-4.c

這次由上到下：

🤯 開頭

GST_DEBUG_CATEGORY_STATIC (debug_category);
#define GST_CAT_DEFAULT debug_category

/*
 * These macros provide a way to store the native pointer to CustomData, which might be 32 or 64 bits, into
 * a jlong, which is always 64 bits, without warnings.
 */
#if GLIB_SIZEOF_VOID_P == 8
# define GET_CUSTOM_DATA(env, thiz, fieldID) (CustomData *)(*env)->GetLongField (env, thiz, fieldID)
# define SET_CUSTOM_DATA(env, thiz, fieldID, data) (*env)->SetLongField (env, thiz, fieldID, (jlong)data)
#else
# define GET_CUSTOM_DATA(env, thiz, fieldID) (CustomData *)(jint)(*env)->GetLongField (env, thiz, fieldID)
# define SET_CUSTOM_DATA(env, thiz, fieldID, data) (*env)->SetLongField (env, thiz, fieldID, (jlong)(jint)data)
#endif

五個輔導的通用文，😁：應該扒拉在另一個檔里，以后直接用 AI 插碼就是了，扔框框比打字強多了，怎么寫 AI，當然是你幫我啦，咱們一起賣，怎樣？

/* Do not allow seeks to be performed closer than this distance. It is visually useless, and will probably
 * confuse some demuxers. */
#define SEEK_MIN_DELAY (500 * GST_MSECOND)

設定跳檔最小的時間是半秒，

…

📊 CustomData

/* Structure to contain all our information, so we can pass it to callbacks */
typedef struct _CustomData
{
  jobject app;                  /* Application instance, used to call its methods. A global reference is kept. */
  GstElement *pipeline;         /* The running pipeline */
  GMainContext *context;        /* GLib context used to run the main loop */
  GMainLoop *main_loop;         /* GLib main loop */
  gboolean initialized;         /* To avoid informing the UI multiple times about the initialization */
  ANativeWindow *native_window; /* The Android native window where video will be rendered */
  GstState state;               /* Current pipeline state */
  GstState target_state;        /* Desired pipeline state, to be set once buffering is complete */
  gint64 duration;              /* Cached clip duration */
  gint64 desired_position;      /* Position to seek to, once the pipeline is running */
  GstClockTime last_seek_time;  /* For seeking overflow prevention (throttling) */
  gboolean is_live;             /* Live streams do not use buffering */
} CustomData;

🗿 舊的：app, pipeline, context, main_loop, initialized, native_window，
🎁 新的：

state：資源狀態
target_state: buffer 之后的狀態
duration：錄像對時
desired_position：跳動的位置
last_seek_time：節流，防止跳錯時間，
is_live：是否純網流，沒有用地方資料儲備？
…

👀 字幕

/* playbin flags */
typedef enum
{
  GST_PLAY_FLAG_TEXT = (1 << 2) /* 要不要字幕 */
} GstPlayFlags;

? Java 引數

/* These global variables cache values which are not changing during execution */
static pthread_t gst_app_thread;
static pthread_key_t current_jni_env;
static JavaVM *java_vm;
static jfieldID custom_data_field_id;
static jmethodID set_message_method_id;
static jmethodID set_current_position_method_id;
static jmethodID on_gstreamer_initialized_method_id;
static jmethodID on_media_size_changed_method_id;

固定引數：gst_app_thread， current_jni_env， java_vm，custom_data_field_id， set_message_method_id， on_gstreamer_initialized_method_id

新增引數：set_current_position_method_id（搜索棍）， on_media_size_changed_method_id（展示螢屏大小）
…

🔁 方程對比

??attach_current_thread() ： 🈚?改變

??detach_current_thread() ： 🈚?改變

??get_jni_env() ： 🈚?改變

??set_ui_message() ： 🈚?改變

…

? set_current_ui_position()，呼叫搜索棍

Java——setCurrentPosition()

static void
set_current_ui_position (gint position, gint duration, CustomData * data)
{
  JNIEnv *env = get_jni_env ();
  (*env)->CallVoidMethod (env, data->app, set_current_position_method_id,
      position, duration);
  if ((*env)->ExceptionCheck (env)) {
    GST_ERROR ("Failed to call Java method");
    (*env)->ExceptionClear (env);
  }
}

? refresh_ui() 重繪螢屏

static gboolean
refresh_ui (CustomData * data)
{
  gint64 current = -1;
  gint64 position;

  /* We do not want to update anything unless we have a working pipeline in the PAUSED or PLAYING state */
  if (!data || !data->pipeline || data->state < GST_STATE_PAUSED)
    return TRUE;

  /* If we didn't know it yet, query the stream duration */
  if (!GST_CLOCK_TIME_IS_VALID (data->duration)) {
    if (!gst_element_query_duration (data->pipeline, GST_FORMAT_TIME,
            &data->duration)) {
      GST_WARNING ("Could not query current duration");
    }
  }

  if (gst_element_query_position (data->pipeline, GST_FORMAT_TIME, &position)) {
    /* Java expects these values in milliseconds, and GStreamer provides nanoseconds */
    set_current_ui_position (position / GST_MSECOND,
        data->duration / GST_MSECOND, data);
  }
  return TRUE;
}

不要更新，條件：沒data，沒資源，在播或者暫停了，
提取時間長度
設定搜索棍

? delayed_seek_cb()，等待搜索棍的資料，

static gboolean delayed_seek_cb (CustomData * data);
static gboolean
delayed_seek_cb (CustomData * data)
{
  GST_DEBUG ("Doing delayed seek to %" GST_TIME_FORMAT,
      GST_TIME_ARGS (data->desired_position));
  execute_seek (data->desired_position, data);
  return FALSE;
}

? execute_seek()，跳到指定位置，

static void
execute_seek (gint64 desired_position, CustomData * data)
{
  gint64 diff;

  if (desired_position == GST_CLOCK_TIME_NONE)
    return;

  diff = gst_util_get_timestamp () - data->last_seek_time;

  if (GST_CLOCK_TIME_IS_VALID (data->last_seek_time) && diff < SEEK_MIN_DELAY) {
    /* The previous seek was too close, delay this one */
    GSource *timeout_source;

    if (data->desired_position == GST_CLOCK_TIME_NONE) {
      /* There was no previous seek scheduled. Setup a timer for some time in the future */
      timeout_source =
          g_timeout_source_new ((SEEK_MIN_DELAY - diff) / GST_MSECOND);
      g_source_set_callback (timeout_source, (GSourceFunc) delayed_seek_cb,
          data, NULL);
      g_source_attach (timeout_source, data->context);
      g_source_unref (timeout_source);
    }
    /* Update the desired seek position. If multiple requests are received before it is time
     * to perform a seek, only the last one is remembered. */
    data->desired_position = desired_position;
    GST_DEBUG ("Throttling seek to %" GST_TIME_FORMAT ", will be in %"
        GST_TIME_FORMAT, GST_TIME_ARGS (desired_position),
        GST_TIME_ARGS (SEEK_MIN_DELAY - diff));
  } else {
    /* Perform the seek now */
    GST_DEBUG ("Seeking to %" GST_TIME_FORMAT,
        GST_TIME_ARGS (desired_position));
    data->last_seek_time = gst_util_get_timestamp ();
    gst_element_seek_simple (data->pipeline, GST_FORMAT_TIME,
        GST_SEEK_FLAG_FLUSH | GST_SEEK_FLAG_KEY_UNIT, desired_position);
    data->desired_position = GST_CLOCK_TIME_NONE;
  }
}

desired_position 等于現狀，你手抖啊？
不一樣：往前跳
不一樣：往后跳
…

??error_cb () ： 🈚?改變

…

? eos_cb()，播完，回頭，暫停，

static void
eos_cb (GstBus * bus, GstMessage * msg, CustomData * data)
{
  data->target_state = GST_STATE_PAUSED;
  data->is_live =
      (gst_element_set_state (data->pipeline,
          GST_STATE_PAUSED) == GST_STATE_CHANGE_NO_PREROLL);
  execute_seek (0, data);
}

? duration_cb()，換片，時間=NONE，

static void
duration_cb (GstBus * bus, GstMessage * msg, CustomData * data)
{
  data->duration = GST_CLOCK_TIME_NONE;
}

? buffering_cb()，掐播至100%buffer

static void
buffering_cb (GstBus * bus, GstMessage * msg, CustomData * data)
{
  gint percent;

  if (data->is_live)
    return;

  gst_message_parse_buffering (msg, &percent);
  if (percent < 100 && data->target_state >= GST_STATE_PAUSED) {
    gchar *message_string = g_strdup_printf ("Buffering %d%%", percent);
    gst_element_set_state (data->pipeline, GST_STATE_PAUSED);
    set_ui_message (message_string, data);
    g_free (message_string);
  } else if (data->target_state >= GST_STATE_PLAYING) {
    gst_element_set_state (data->pipeline, GST_STATE_PLAYING);
  } else if (data->target_state >= GST_STATE_PAUSED) {
    set_ui_message ("Buffering complete", data);
  }
}

? clock_lost_cb()，時間消失，先停再放，

static void
clock_lost_cb (GstBus * bus, GstMessage * msg, CustomData * data)
{
  if (data->target_state >= GST_STATE_PLAYING) {
    gst_element_set_state (data->pipeline, GST_STATE_PAUSED);
    gst_element_set_state (data->pipeline, GST_STATE_PLAYING);
  }
}

? check_media_size()，測出片子長寬，

static void
check_media_size (CustomData * data)
{
  JNIEnv *env = get_jni_env ();
  GstElement *video_sink;
  GstPad *video_sink_pad;
  GstCaps *caps;
  GstVideoInfo info;

  /* Retrieve the Caps at the entrance of the video sink */
  g_object_get (data->pipeline, "video-sink", &video_sink, NULL);
  video_sink_pad = gst_element_get_static_pad (video_sink, "sink");
  caps = gst_pad_get_current_caps (video_sink_pad);

  if (gst_video_info_from_caps (&info, caps)) {
    info.width = info.width * info.par_n / info.par_d;
    GST_DEBUG ("Media size is %dx%d, notifying application", info.width,
        info.height);

    (*env)->CallVoidMethod (env, data->app, on_media_size_changed_method_id,
        (jint) info.width, (jint) info.height);
    if ((*env)->ExceptionCheck (env)) {
      GST_ERROR ("Failed to call Java method");
      (*env)->ExceptionClear (env);
    }
  }

  gst_caps_unref (caps);
  gst_object_unref (video_sink_pad);
  gst_object_unref (video_sink);
}

Caps 的求法：video_sink => video_sink_pad => caps
有東西，就呼叫 Java——onMediaSizeChanged() ，
Caps 清理：刪 caps，刪 video_sink_pad，刪 video_sink ，
…

? state_changed_cb()，暫停，執行搜索棍的命令，

    /* The Ready to Paused state change is particularly interesting: */
    if (old_state == GST_STATE_READY && new_state == GST_STATE_PAUSED) {
      /* By now the sink already knows the media size */
      check_media_size (data);

      /* If there was a scheduled seek, perform it now that we have moved to the Paused state */
      if (GST_CLOCK_TIME_IS_VALID (data->desired_position))
        execute_seek (data->desired_position, data);
    }

…

??check_initialization_complete() ： 🈚?改變

…

? app_function()，增加時間控制

static void *
app_function (void *userdata)
{
  JavaVMAttachArgs args;
  GstBus *bus;
  CustomData *data = (CustomData *) userdata;
  GSource *timeout_source;
  GSource *bus_source;
  GError *error = NULL;
  guint flags;
  GST_DEBUG ("Creating pipeline in CustomData at %p", data);

  /* Create our own GLib Main Context and make it the default one */
  data->context = g_main_context_new ();
  g_main_context_push_thread_default (data->context);

多了 timeout_resouce 和 flags，

  /* Build pipeline */
  data->pipeline = gst_parse_launch ("playbin", &error);
  if (error) {
    gchar *message =
        g_strdup_printf ("Unable to build pipeline: %s", error->message);
    g_clear_error (&error);
    set_ui_message (message, data);
    g_free (message);
    return NULL;
  }

pipeline 使用 playbin 運行，error 檢測還是一樣的，

  /* Disable subtitles */
  g_object_get (data->pipeline, "flags", &flags, NULL);
  flags &= ~GST_PLAY_FLAG_TEXT;
  g_object_set (data->pipeline, "flags", flags, NULL);

無字幕，

  /* Set the pipeline to READY, so it can already accept a window handle, if we have one */
  data->target_state = GST_STATE_READY;
  gst_element_set_state (data->pipeline, GST_STATE_READY);

pipeline 進入備戰狀態，

  /* Instruct the bus to emit signals for each received message, and connect to the interesting signals */
  bus = gst_element_get_bus (data->pipeline);
  bus_source = gst_bus_create_watch (bus);
  g_source_set_callback (bus_source, (GSourceFunc) gst_bus_async_signal_func,
      NULL, NULL);
  g_source_attach (bus_source, data->context);
  g_source_unref (bus_source);
  g_signal_connect (G_OBJECT (bus), "message::error", (GCallback) error_cb,
      data);
  g_signal_connect (G_OBJECT (bus), "message::eos", (GCallback) eos_cb, data);
  g_signal_connect (G_OBJECT (bus), "message::state-changed",
      (GCallback) state_changed_cb, data);
  g_signal_connect (G_OBJECT (bus), "message::duration",
      (GCallback) duration_cb, data);
  g_signal_connect (G_OBJECT (bus), "message::buffering",
      (GCallback) buffering_cb, data);
  g_signal_connect (G_OBJECT (bus), "message::clock-lost",
      (GCallback) clock_lost_cb, data);
  gst_object_unref (bus);

  /* Register a function that GLib will call 4 times per second */
  timeout_source = g_timeout_source_new (250);
  g_source_set_callback (timeout_source, (GSourceFunc) refresh_ui, data, NULL);
  g_source_attach (timeout_source, data->context);
  g_source_unref (timeout_source);

bus 快遞增加 **eos_cb（播完回呼），duration_cb（換片回呼）， buffering_cb（下載回呼）， clock_lost_cb（失時回呼）**四個郵件，
時間顯示每隔 1/4 秒更新一次，
…
main_loop 部分：🈚?改變，
垃圾清理部分： 🈚?改變，
…

? gst_native_init()，多了兩個引數

static void
gst_native_init (JNIEnv * env, jobject thiz)
{
  CustomData *data = g_new0 (CustomData, 1);
  data->desired_position = GST_CLOCK_TIME_NONE;
  data->last_seek_time = GST_CLOCK_TIME_NONE;
  ...
}

desired_position 希望位置 = 無
last_seek_time 上次搜索時間 = 無
…

??gst_native_finalize() 🈚?改變

…

? gst_native_set_uri()，設定網址

void
gst_native_set_uri (JNIEnv * env, jobject thiz, jstring uri)
{
  CustomData *data = GET_CUSTOM_DATA (env, thiz, custom_data_field_id);
  if (!data || !data->pipeline)
    return;
  const gchar *char_uri = (*env)->GetStringUTFChars (env, uri, NULL);
  GST_DEBUG ("Setting URI to %s", char_uri);
  if (data->target_state >= GST_STATE_READY)
    gst_element_set_state (data->pipeline, GST_STATE_READY);
  g_object_set (data->pipeline, "uri", char_uri, NULL);
  (*env)->ReleaseStringUTFChars (env, uri, char_uri);
  data->duration = GST_CLOCK_TIME_NONE;
  data->is_live =
      (gst_element_set_state (data->pipeline,
          data->target_state) == GST_STATE_CHANGE_NO_PREROLL);
}

char_uri 由 Java uri 換過來的，
…

? gst_native_play，增加 is_live 活著嗎？

static void
gst_native_play (JNIEnv * env, jobject thiz)
{
  ...
  data->target_state = GST_STATE_PLAYING;
  data->is_live =
      (gst_element_set_state (data->pipeline,
          GST_STATE_PLAYING) == GST_STATE_CHANGE_NO_PREROLL);
}

? gst_native_pause，增加 is_live 活著嗎？

static void
gst_native_pause (JNIEnv * env, jobject thiz)
{
  ...
  data->target_state = GST_STATE_PAUSED;
  data->is_live =
      (gst_element_set_state (data->pipeline,
          GST_STATE_PAUSED) == GST_STATE_CHANGE_NO_PREROLL);
}

? gst_native_set_position，搜索棍位置

void
gst_native_set_position (JNIEnv * env, jobject thiz, int milliseconds)
{
  CustomData *data = GET_CUSTOM_DATA (env, thiz, custom_data_field_id);
  if (!data)
    return;
  gint64 desired_position = (gint64) (milliseconds * GST_MSECOND);
  if (data->state >= GST_STATE_PAUSED) {
    execute_seek (desired_position, data);
  } else {
    GST_DEBUG ("Scheduling seek to %" GST_TIME_FORMAT " for later",
        GST_TIME_ARGS (desired_position));
    data->desired_position = desired_position;
  }
}

? gst_native_class_init，增加了兩個 Java 方程

static jboolean
gst_native_class_init (JNIEnv * env, jclass klass)
{
  custom_data_field_id =
      (*env)->GetFieldID (env, klass, "native_custom_data", "J");
  set_message_method_id =
      (*env)->GetMethodID (env, klass, "setMessage", "(Ljava/lang/String;)V");
  set_current_position_method_id =
      (*env)->GetMethodID (env, klass, "setCurrentPosition", "(II)V");
  on_gstreamer_initialized_method_id =
      (*env)->GetMethodID (env, klass, "onGStreamerInitialized", "()V");
  on_media_size_changed_method_id =
      (*env)->GetMethodID (env, klass, "onMediaSizeChanged", "(II)V");

  if (!custom_data_field_id || !set_message_method_id
      || !on_gstreamer_initialized_method_id || !on_media_size_changed_method_id
      || !set_current_position_method_id) {
    /* We emit this message through the Android log instead of the GStreamer log because the later
     * has not been initialized yet.
     */
    LOGE("%s", "tutorial-4: The calling class does not implement "
               "all necessary interface methods");
    return JNI_FALSE;
  }
  return JNI_TRUE;
}

Java： setCurrentPosition(), onMediaSizeChanged()
…

??gst_native_surface_init() ： 🈚?改變

??gst_native_surface_finalize () ： 🈚?改變

…

? native_methods[]，增加兩個引數

static JNINativeMethod native_methods[] = {
  {"nativeInit", "()V", (void *) gst_native_init},
  {"nativeFinalize", "()V", (void *) gst_native_finalize},
  {"nativeSetUri", "(Ljava/lang/String;)V", (void *) gst_native_set_uri},
  {"nativePlay", "()V", (void *) gst_native_play},
  {"nativePause", "()V", (void *) gst_native_pause},
  {"nativeSetPosition", "(I)V", (void *) gst_native_set_position},
  {"nativeSurfaceInit", "(Ljava/lang/Object;)V",
      (void *) gst_native_surface_init},
  {"nativeSurfaceFinalize", "()V", (void *) gst_native_surface_finalize},
  {"nativeClassInit", "()Z", (void *) gst_native_class_init}
};

增加：

nativeSetUri => gst_native_set_uri()
nativeSetPosition => gst_native_set_position()

…

??JNI_OnLoad ()： 🈚?改變

…

💿5. Andoird.mk

跟 輔導三 沒多大區別，NDKBuild 模式都是差不多，不同的是結尾：

GSTREAMER_NDK_BUILD_PATH  := $(GSTREAMER_ROOT)/share/gst-android/ndk-build/
include $(GSTREAMER_NDK_BUILD_PATH)/plugins.mk
GSTREAMER_PLUGINS         := $(GSTREAMER_PLUGINS_CORE) $(GSTREAMER_PLUGINS_PLAYBACK) $(GSTREAMER_PLUGINS_CODECS) $(GSTREAMER_PLUGINS_NET) $(GSTREAMER_PLUGINS_SYS)
G_IO_MODULES              := openssl
GSTREAMER_EXTRA_DEPS      := gstreamer-video-1.0
include $(GSTREAMER_NDK_BUILD_PATH)/gstreamer-1.0.mk

IO 用 openssl 加密，

🌁 6. 用 Hilt + MVVM 建架構(自找麻煩）

🔻維修警告：請先備份💾 —— 上傳到 GitHub，或者你的云服務器，

🧺 Gradle

🔌 Project: Build.gradle

🟢? Hilt 外掛：

buildscript {
    ext.kotlin_version = "1.4.30"
    repositories {
        google()
        jcenter()
        mavenCentral()
        maven { url "https://oss.jfrog.org/libs-snapshot" }
    }

    ext.hilt_version = '2.29-alpha'
    dependencies {
        classpath 'com.android.tools.build:gradle:4.2.0-alpha15'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"

        // Hilt
        classpath "com.google.dagger:hilt-android-gradle-plugin:$hilt_version"
    }
}

…

🔌 Tutorial-4 Module: Build.gradle

🟢? ConstraintLayout：

dependencies {
...
    // Design
    implementation 'com.google.android.material:material:1.2.1'
    // Layout
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
}

🟢? Java 1.8 ：

android {
...
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }
}

🟢? Dagger-Hilt+Lifecycle:

plugins {
    id 'com.android.application'
    id 'kotlin-android'
    id 'kotlin-kapt'
    id 'dagger.hilt.android.plugin'
}
...
dependencies {
...
    // Hilt
    implementation "com.google.dagger:hilt-android:$hilt_version"
    kapt "com.google.dagger:hilt-android-compiler:$hilt_version"
    // Hilt+Lifecycle
    def hilt_lifecycle_version = '1.0.0-alpha03'
    implementation "androidx.hilt:hilt-lifecycle-viewmodel:$hilt_lifecycle_version"
    kapt "androidx.hilt:hilt-compiler:$hilt_lifecycle_version"
    // Hilt+Tests
    androidTestImplementation "com.google.dagger:hilt-android-testing:$hilt_version"
    kaptAndroidTest "com.google.dagger:hilt-android-compiler:$hilt_version"

    // by viewModels() ext
    def activity_version = "1.2.0-rc01"
    def fragment_version = "1.3.0-rc02"
    implementation "androidx.activity:activity-ktx:$activity_version"
    implementation "androidx.fragment:fragment-ktx:$fragment_version"

    // Lifecycle
    def lifecycle_ktx = '2.3.0'
    implementation "androidx.lifecycle:lifecycle-runtime-ktx:$lifecycle_ktx"
    implementation "androidx.lifecycle:lifecycle-livedata-ktx:$lifecycle_ktx"
    implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycle_ktx"

}

Sync，🔺🏃跑一次，OK 就備份💾，
😑：你們用過 Dagger 的都知道，它太挑剔了，跑成一次，備份一次絕對沒錯，
…

💊 PlayerApp

app
🟢? 路：application
🟢? app：PlayerApp

@HiltAndroidApp
class PlayerApp: Application()

🟢? name：AndroidManifest

…

? PlayerViewModel

在 Tutorial4.kt 旁邊加 PlayerViewModel.kt：

新版 Hilt 又改名了，讓我好查：@ViewModelInject 改成 @HiltViewModel
🙄：你瞧瞧，人家 Hilt 小隊終于正名了！這跟 此山是我開，此樹是我栽 一個意思，

@HiltViewModel
class PlayerViewModel: ViewModel() {
}

加進 Tutorial4:

@AndroidEntryPoint
class Tutorial4 : AppCompatActivity(), SurfaceHolder.Callback, OnSeekBarChangeListener {
    // VM
    private val playerVM: PlayerViewModel by viewModels()

🟢? 那個 Activity() 改 AppCompatActivity()，
🟢? @AndroidEntryPoint
🟢? private val playerVM: PlayerViewModel by viewModels()
這個 viewModels() 是屬于 MVVM 一部分，androidx.activity:activity-ktx 或者 androidx.fragment:fragment-ktx 的👶🏻仔，

🔺 🏃跑一遍，備份💾，

🍗7. 組裝 GStreamer 牌播放器，

😋：呵呵，我這篇文章最適合胖子讀，有雞腿吃，

🤖1. Android.mk

改名也，誰還叫 tutorial-4 ？如果別人問你寫了什么？你回答：“嗯， Tutorial4 播放器…”
🧒：什么玩意兒？

LOCAL_MODULE    := player
LOCAL_SRC_FILES := player.c dummy.cpp

在開頭換，把 tutorial-4.c 改名 player.c ，

在這里插入代碼片

接著跑🏃啊！

> Unexpected native build target tutorial-4. Valid values are: gstreamer_android, player

👸：啊！死啦死啦的，Bug 來啦！看我九陰白骨爪！
👦：抓我干嘛咧？不是蟑螂啦，Build target？是 gradle 蟲啦！

externalNativeBuild {
            ndkBuild {
                def gstRoot

                if (project.hasProperty('gstAndroidRoot'))
                    gstRoot = project.gstAndroidRoot
                else
                    gstRoot = System.env.GSTREAMER_ROOT_ANDROID

                if (gstRoot == null)
                    throw new Exception('GSTREAMER_ROOT_ANDROID must be set, or "gstAndroidRoot" must be defined in your gradle.properties in the top level directory of the unpacked universal GStreamer Android binaries')

                arguments "NDK_APPLICATION_MK=jni/Application.mk", "GSTREAMER_JAVA_SRC_DIR=src", "GSTREAMER_ROOT_ANDROID=$gstRoot", "GSTREAMER_ASSETS_DIR=src/assets"

                targets "tutorial-4"

                // All archs except MIPS and MIPS64 are supported
                abiFilters  'armeabi-v7a', 'arm64-v8a', 'x86', 'x86_64'
            }
        }

這 targets 還粘著 tutorial-4 的標簽，那就換成 player 吧，

targets "player"

Sync，跑🏃， pass ！備份💾，

總結：在 NDKBuild 中，這幾個檔案一定要用同名組件：

Android.mk —— LOCAL_MODULE :=abc
Gradel Module —— externalNativeBuild { ndkBuild { targets “abc” } }
Java class with NDK call —— ?System.loadLibrary(“abc”)

…

??2. 撕開 Tutorial4.kt，用 NativePlayer 裝

瞧瞧開頭 native- 牌子的，

    private external fun nativeInit() // Initialize native code, build pipeline, etc
    private external fun nativeFinalize() // Destroy pipeline and shutdown native code
    private external fun nativeSetUri(uri: String?) // Set the URI of the media to play
    private external fun nativePlay() // Set pipeline to PLAYING
    private external fun nativeSetPosition(milliseconds: Int) // Seek to the indicated position, in milliseconds
    private external fun nativePause() // Set pipeline to PAUSED
    private external fun nativeSurfaceInit(surface: Any) // A new surface is available
    private external fun nativeSurfaceFinalize() // Surface about to be destroyed
    private val native_custom_data // Native code will use this to keep private data
            : Long = 0
    private var is_playing_desired // Whether the user asked to go to PLAYING
            = false
    private var position // Current position, reported by native code
            = 0
    private var duration // Current clip duration, reported by native code
            = 0
    private var is_local_media // Whether this clip is stored locally or is being streamed
            = false
    private var desired_position // Position where the users wants to seek to
            = 0
    private var mediaUri // URI of the clip being played
            : String? = null
    private val defaultMediaUri =
        "https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.ogv"

都搬，起個名，喚 NativePalyer.kt ，開條路，叫 player ，
player
可是方程名字是🔥紅色的，
把

    companion object {
        @JvmStatic
        private external fun nativeClassInit(): Boolean // Initialize native class: cache Method IDs for callbacks

        init {
            System.loadLibrary("gstreamer_android")
            System.loadLibrary("tutorial-4")
            nativeClassInit()
        }
    }

搬過去，🔥紅色的，
噢，名字沒改，

System.loadLibrary("player")

🔥紅色的，還六親不認啦！
看看 player.c ，所有 JNI 都在 JNI_OnLoad 開始，

  jclass klass = (*env)->FindClass (env,
      "org/freedesktop/gstreamer/tutorials/tutorial_4/Tutorial4");

找到 Tutorial4 的🧟僵尸了，
道長👲：道可道，非常道，妖孽，看符！打打打…
導演🙊：🙈

  jclass klass = (*env)->FindClass (env,
      "org/freedesktop/gstreamer/tutorials/tutorial_4/player/NativePlayer");

把 NativePlayer 加進 Tutorial4 ：

class Tutorial4 : AppCompatActivity(), SurfaceHolder.Callback, SeekBar.OnSeekBarChangeListener {
    // VM
    private val playerVM: PlayerViewModel by viewModels()
    
    // NativePlayer
    private val nplayer = NativePlayer()

紅色消失了，不知道你的會不會，不過現在還沒搬完，

📢在 NativePlayer 加 public 使用方式

    // native fun
    private external fun nativeInit() // Initialize native code, build pipeline, etc
    fun initJni() { nativeInit() }

    private external fun nativeFinalize() // Destroy pipeline and shutdown native code
    fun finalize() { nativeFinalize() }

    private external fun nativeSetUri(uri: String?) // Set the URI of the media to play
    fun setUri(uri: String?) { nativeSetUri(uri) }

    private external fun nativePlay() // Set pipeline to PLAYING
    fun play() { nativePlay() }

    private external fun nativeSetPosition(milliseconds: Int) // Seek to the indicated position, in milliseconds
    fun setPos(ms: Int) { nativeSetPosition(ms) }

    private external fun nativePause() // Set pipeline to PAUSED
    fun pause() { nativePause() }

    private external fun nativeSurfaceInit(surface: Any) // A new surface is available
    fun initSurface(surface: Any) { nativeSurfaceInit(surface) }

    private external fun nativeSurfaceFinalize() // Destroy surface
    fun surfaceFinalize() { nativeSurfaceFinalize() }

private 嘛，當然要加公用方式，

…

🔂連接 NativePlayer 到 Tutorial4 的方程

?? setMessage()

這個簡單，加 MutableLiveData ，

PlayerViewModel：觀察點

    val message = MutableLiveData<String>()

    init {
        message.value = ""
    }

NatviePlayer：要搭載 VM 輸出資料，

    // inject vm
    lateinit var vm: PlayerViewModel
    fun setVM(vm: PlayerViewModel) { this.vm = vm }

移植 setMessage ：

NatviePlayer：輸出 JNI 的資料

    fun setMessage(inMessage: String) {
        vm.message.postValue(inMessage)
    }

Tutorial4——onCreate()：觀察員

        // observer
        playerVM.message.observe(this, {
            msgTV.text = it
        })

…

?? setMediaUri()

搬到 NativePlayer，加默認網址，

    fun setMediaUri() {
        if (mediaUri == null || mediaUri!!.isEmpty())
            mediaUri = defaultMediaUri
        nativeSetUri(mediaUri)
        is_local_media = mediaUri!!.startsWith("file://")
    }

? onGStreamerInitialized()

移動到 NativePlayer

    private fun onGStreamerInitialized() {
        lgi("GStreamer -- GStreamer initialized:")
        lgi("GStreamer --\nplaying:$is_playing_desired\nposition:$position\nuri: $mediaUri")

        // Restore previous playing state
        setMediaUri()
        nativeSetPosition(position)
        if (is_playing_desired) {
            nativePlay()
        } else {
            nativePause()
        }

        vm.gstInitialized.postValue(true)
    }

PlayerViewModel ：觀察點

    // player data
    val message = MutableLiveData<String>()
    val gstInitialized = MutableLiveData<Boolean>()

    init {
        message.value = ""
        gstInitialized.value = false
    }

Tutorial4——onCreate()：觀察員

        // observers
        playerVM.message.observe(this, {...})
        // initialize GStreamer
        playerVM.gstInitialized.observe(this, {
            runOnUiThread {
                play.isEnabled = true
                pause.isEnabled = true
            }
        })

🆕 updateTimeWidget()

更新：

    @SuppressLint("SimpleDateFormat")
    fun updateTimeWidget() {
        val pos = sb.progress
        val df = SimpleDateFormat("HH:mm:ss")
        df.timeZone = TimeZone.getTimeZone("UTC")
        val message = df.format( Date(pos.toLong()) ) +
                " / " + df.format(Date(nplayer.duration.toLong()))
        timeTV.text = message
    }

🔰setCurrentPosition()

洗掉在 Tutorial4 的 setCurrentPosition() ，

NativePlayer：

var seekbarPressed = false
fun setCurrentPosition(position:Int, duration:Int) {
    if (seekbarPressed) return

    // update seekbar
    vm.seekb.postValue(SeekData(position, duration))
    this.position = position
    this.duration = duration
}

增加 SeekData.kt 記錄資料：

data class SeekData(
    val position:Int,
    val duration:Int)

PlayerViewModel：觀察點

// player data
val message = MutableLiveData<String>()
val gstInitialized = MutableLiveData<Boolean>()
val seekb = MutableLiveData<SeekData>()

Tutorial4——onCreate()：觀察員

// initialize GStreamer
playerVM.gstInitialized.observe(this, {...})
// update seekbar
playerVM.seekb.observe(this, {
    sb.max = it.duration
    sb.progress = it.position
    updateTimeWidget()
})

🔲 SurfaceView

    override fun surfaceChanged(
        holder: SurfaceHolder, format: Int, width: Int,
        height: Int
    ) {
        lgd("GStreamer -- Surface changed to format " + format + " width "
                    + width + " height " + height
        )
        nplayer.initSurface(holder.surface)
    }

    override fun surfaceCreated(holder: SurfaceHolder) {
        lgd("GStreamer -- Surface created: " + holder.surface)
    }

    override fun surfaceDestroyed(holder: SurfaceHolder) {
        lgd("GStreamer -- Surface destroyed")
        nplayer.surfaceFinalize()
    }

📏 onMediaSizeChanged()

這是設定播放尺寸，將它洗掉，

轉移到 NativePlayer ：

private fun onMediaSizeChanged(width: Int, height: Int) {
    lgi("GStreamer--Media size changed to " + width + "x" + height)
    val mediaSize = MediaSize(width, height)
    vm.mediaSize.postValue(mediaSize)
}

在 player 里面，建立 MediaSize.kt ：

data class MediaSize(
    val width:Int,
    val height:Int)

PlayerViewModel ：觀察點

    val seekb = MutableLiveData<SeekData>()
    val mediaSize = MutableLiveData<MediaSize>()

Tutorial4——onCreate()：觀察員

        // update seekbar
        playerVM.seekb.observe(this, {...})
        // get media size to surfaceview
        playerVM.mediaSize.observe(this, {
            gsv.media_width = it.width
            gsv.media_height = it.height
            runOnUiThread { gsv.requestLayout() }
        })

? Seekbar

更新：

    // The Seek Bar thumb has moved, either because the user dragged it or we have called setProgress()
    override fun onProgressChanged(sb: SeekBar, progress: Int, fromUser: Boolean) {
        if (!fromUser) return
        nplayer.desired_position = progress
        // If this is a local file, allow scrub seeking, this is, seek as soon as the slider is moved.
        if (nplayer.is_local_media)
            nplayer.setPos(nplayer.desired_position)
        nplayer.seekbarPressed = sb.isPressed
        updateTimeWidget()
    }

    // The user started dragging the Seek Bar thumb
    override fun onStartTrackingTouch(sb: SeekBar) {
        nplayer.pause()
        nplayer.seekbarPressed = sb.isPressed
    }

    // The user released the Seek Bar thumb
    override fun onStopTrackingTouch(sb: SeekBar) {
        // If this is a remote file, scrub seeking is probably not going to work smoothly enough.
        // Therefore, perform only the seek when the slider is released.
        nplayer.seekbarPressed = sb.isPressed
        if (!nplayer.is_local_media)
            nplayer.setPos(nplayer.desired_position)
        if (nplayer.is_playing_desired)
            nplayer.play()
    }

🔺 🏃跑一遍，備份💾，
…

🍤這一篇太長了，要加版 T2

縮水英文版

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GStreamer 安卓安裝輔導四：這個播放器不好吃，塞牙縫，來根 ViewModel 牌牙簽，將 GStreamer 剔出來。