GStreamer —— 2.13、Windows下Qt加载GStreamer库后运行 - “教程13:播放控制“（附：完整源码）

运行效果(音频)

 

简介

     上一个教程演示了GStreamer工具。本教程介绍视频播放控制。快进、反向播放和慢动作都是技术 统称为 Trick Modes，它们都有一个共同点 修改 Normal playback rate。本教程介绍如何实现 这些效果并在交易中添加了帧步进。特别是，它 显示：

          • 如何更改播放速率，比正常更快和更慢， 前进和向后。

          • 如何逐帧推进视频

 

     快进是一种以高于 它的正常（预期）速度;而慢动作使用低于 预期的那个。反向播放执行相同的作，但向后播放， 从流的结尾到开头。所有这些技术所做的只是更改播放速率，这是一个变量 等于 1.0 表示正常播放，大于 1.0（绝对值） 对于快速模式，对于慢速模式，低于 1.0（绝对值）， positive 表示正向播放，negative 表示反向播放。GStreamer 提供了两种机制来更改播放速率：步进 事件 （Events） 和查找事件 （Seek Events）。Step Events 允许跳过给定数量的 媒体，除了更改后续播放速率（仅为正数 值）。此外，Seek Events 还允许跳转到 流式传输并设置正播放速率和负播放速率。

 

GStreamer相关运行库

INCLUDEPATH += D:/Software/GStreamer/1.0/mingw_x86_64/include/gstreamer-1.0/gst
INCLUDEPATH += D:/Software/GStreamer/1.0/mingw_x86_64/include
INCLUDEPATH += D:/Software/GStreamer/1.0/mingw_x86_64/include/gstreamer-1.0
INCLUDEPATH += D:/Software/GStreamer/1.0/mingw_x86_64/include/glib-2.0
INCLUDEPATH += D:/Software/GStreamer/1.0/mingw_x86_64/lib/glib-2.0/include

LIBS += D:/Software/GStreamer/1.0/mingw_x86_64/lib/gstreamer-1.0.lib
LIBS += D:/Software/GStreamer/1.0/mingw_x86_64/lib/glib-2.0.lib
LIBS += D:/Software/GStreamer/1.0/mingw_x86_64/lib/gobject-2.0.lib

 

完整源码

#include <string.h>
#include <stdio.h>
#include <gst/gst.h>

#ifdef __APPLE__
#include <TargetConditionals.h>
#endif

typedef struct _CustomData
{
    GstElement *pipeline;
    GstElement *video_sink;
    GMainLoop *loop;

    gboolean playing;             /* 播放或暂停 */
    gdouble rate;                 /* 当前播放速率（可以为负） */
} CustomData;

/* Send seek event to change rate */
static void
send_seek_event (CustomData * data)
{
    gint64 position;
    GstEvent *seek_event;

    /* Obtain the current position, needed for the seek event */
    if (!gst_element_query_position (data->pipeline, GST_FORMAT_TIME, &position)) {
        g_printerr ("Unable to retrieve current position.\n");
        return;
    }

    /* Create the seek event */
    if (data->rate > 0) {
        seek_event =
                gst_event_new_seek (data->rate, GST_FORMAT_TIME,
                                    (GstSeekFlags)(GST_SEEK_FLAG_FLUSH | GST_SEEK_FLAG_ACCURATE), GST_SEEK_TYPE_SET,
                                    position, GST_SEEK_TYPE_END, 0);
    } else {
        seek_event =
                gst_event_new_seek (data->rate, GST_FORMAT_TIME,
                                    GstSeekFlags(GST_SEEK_FLAG_FLUSH | GST_SEEK_FLAG_ACCURATE), GST_SEEK_TYPE_SET, 0,
                                    GST_SEEK_TYPE_SET, position);
    }

    if (data->video_sink == NULL) {
        /* If we have not done so, obtain the sink through which we will send the seek events */
        g_object_get (data->pipeline, "video-sink", &data->video_sink, NULL);
    }

    /* Send the event */
    gst_element_send_event (data->video_sink, seek_event);

    g_print ("Current rate: %g\n", data->rate);
}

/* 处理键盘输入 */
static gboolean
handle_keyboard (GIOChannel * source, GIOCondition cond, CustomData * data)
{
    gchar *str = NULL;
    if (g_io_channel_read_line (source, &str, NULL, NULL, NULL) != G_IO_STATUS_NORMAL) { return TRUE; }

    switch (g_ascii_tolower (str[0]))
    {
    case 'p':
        data->playing = !data->playing;
        gst_element_set_state (data->pipeline, data->playing ? GST_STATE_PLAYING : GST_STATE_PAUSED);
        g_print ("Setting state to %s\n", data->playing ? "PLAYING" : "PAUSE"); break;
    case 's':
        if (g_ascii_isupper (str[0]))
        {
            data->rate *= 2.0;
        }
        else
        {
            data->rate /= 2.0;
        }
        send_seek_event (data); break;
    case 'd':
        data->rate *= -1.0; send_seek_event (data);  break;
    case 'n':
        if (data->video_sink == NULL)
        {
            /* If we have not done so, obtain the sink through which we will send the step events */
            g_object_get (data->pipeline, "video-sink", &data->video_sink, NULL);
        }

        gst_element_send_event (data->video_sink,gst_event_new_step (GST_FORMAT_BUFFERS, 1, ABS (data->rate), TRUE,FALSE));
        g_print ("Stepping one frame\n");
        break;
    case 'q':
        g_main_loop_quit (data->loop);
        break;
    default:
        break;
    }

    g_free (str);

    return TRUE;
}

int tutorial_main (int argc, char *argv[])
{
    /* 初始化GStreamer */
    gst_init (&argc, &argv);

    /* 初始化自定义数据 */
    CustomData data;
    memset (&data, 0, sizeof (data));

    /* 输出使用方式 */
    g_print ("USAGE: Choose one of the following options, then press enter:\n"
             " 'P' to toggle between PAUSE and PLAY\n"
             " 'S' to increase playback speed, 's' to decrease playback speed\n"
             " 'D' to toggle playback direction\n"
             " 'N' to move to next frame (in the current direction, better in PAUSE)\n"
             " 'Q' to quit\n");

    /* 构建管道 */
    data.pipeline =
            gst_parse_launch
            ("playbin uri=https://gstreamer.freedesktop.org/data/media/sintel_trailer-480p.webm", NULL);

    /* 增加键盘输入以进行控制 */
#ifdef G_OS_WIN32
    GIOChannel *io_stdin = g_io_channel_win32_new_fd (fileno (stdin));
#else
    GIOChannel *io_stdin = g_io_channel_unix_new (fileno (stdin));
#endif
    g_io_add_watch (io_stdin, G_IO_IN, (GIOFunc) handle_keyboard, &data);

    /* 开始播放 */
    GstStateChangeReturn ret = gst_element_set_state (data.pipeline, GST_STATE_PLAYING);
    if (ret == GST_STATE_CHANGE_FAILURE)
    {
        g_printerr ("Unable to set the pipeline to the playing state.\n");
        gst_object_unref (data.pipeline); return -1;
    }
    data.playing = TRUE;
    data.rate = 1.0;

    /* 创建GLib主循环并将其设置为运行 */
    data.loop = g_main_loop_new (NULL, FALSE);
    g_main_loop_run (data.loop);

    /* 释放资源 */
    g_main_loop_unref (data.loop);
    g_io_channel_unref (io_stdin);
    gst_element_set_state (data.pipeline, GST_STATE_NULL);
    if (data.video_sink != NULL)
        gst_object_unref (data.video_sink);
    gst_object_unref (data.pipeline);
    return 0;
}

int main (int argc, char *argv[])
{
#if defined(__APPLE__) && TARGET_OS_MAC && !TARGET_OS_IPHONE
    return gst_macos_main ((GstMainFunc) tutorial_main, argc, argv, NULL);
#else
    return tutorial_main (argc, argv);
#endif
}

 

关注

笔者 - jxd