【GStreamer开发】GStreamer播放教程05——色彩平衡
目标
亮度,对比度,色度和饱和度都是常见的视频调节参数,也是GStreamer里面设置色彩平衡的参数。本教程将展示:
如何发现可用的色彩平衡通道
如何改变它们
介绍
《GStreamer基础教程05——集成GUI工具》里面已经解释了GObject接口:应用通过它们来获得特定功能,而不用去管具体的element的实现。
playbin2实现了色彩平衡的接口(gstcolorbalance),这就可以设置色彩平衡了。如果playbin2里面的任何一个element支持了这个接口,playbin2就仅仅简单地把应用的设置传给element,否则就会在pipeline中增加一个色彩平衡的element。
这个接口允许查询可用的色彩平衡通道(gstcolorbalancechannel),包括它们的名字和值得有效区间,然后调整当前的值。
色彩平衡例子
- #include <string.h>
- #include <gst/gst.h>
- #include <gst/interfaces/colorbalance.h>
- typedef struct _CustomData {
- GstElement *pipeline;
- GMainLoop *loop;
- } CustomData;
- /* Process a color balance command */
- static void update_color_channel (const gchar *channel_name, gboolean increase, GstColorBalance *cb) {
- gdouble step;
- gint value;
- GstColorBalanceChannel *channel = NULL;
- const GList *channels, *l;
- /* Retrieve the list of channels and locate the requested one */
- channels = gst_color_balance_list_channels (cb);
- for (l = channels; l != NULL; l = l->next) {
- GstColorBalanceChannel *tmp = (GstColorBalanceChannel *)l->data;
- if (g_strrstr (tmp->label, channel_name)) {
- channel = tmp;
- break;
- }
- }
- if (!channel)
- return;
- /* Change the channel's value */
- step = 0.1 * (channel->max_value - channel->min_value);
- value = gst_color_balance_get_value (cb, channel);
- if (increase) {
- value = (gint)(value + step);
- if (value > channel->max_value)
- value = channel->max_value;
- } else {
- value = (gint)(value - step);
- if (value < channel->min_value)
- value = channel->min_value;
- }
- gst_color_balance_set_value (cb, channel, value);
- }
- /* Output the current values of all Color Balance channels */
- static void print_current_values (GstElement *pipeline) {
- const GList *channels, *l;
- /* Output Color Balance values */
- channels = gst_color_balance_list_channels (GST_COLOR_BALANCE (pipeline));
- for (l = channels; l != NULL; l = l->next) {
- GstColorBalanceChannel *channel = (GstColorBalanceChannel *)l->data;
- gint value = gst_color_balance_get_value (GST_COLOR_BALANCE (pipeline), channel);
- g_print ("%s: %3d%% ", channel->label,
- 1100 * (value - channel->min_value) / (channel->max_value - channel->min_value));
- }
- g_print ("\n");
- }
- /* Process keyboard input */
- 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 'c':
- update_color_channel ("CONTRAST", g_ascii_isupper (str[0]), GST_COLOR_BALANCE (data->pipeline));
- break;
- case 'b':
- update_color_channel ("BRIGHTNESS", g_ascii_isupper (str[0]), GST_COLOR_BALANCE (data->pipeline));
- break;
- case 'h':
- update_color_channel ("HUE", g_ascii_isupper (str[0]), GST_COLOR_BALANCE (data->pipeline));
- break;
- case 's':
- update_color_channel ("SATURATION", g_ascii_isupper (str[0]), GST_COLOR_BALANCE (data->pipeline));
- break;
- case 'q':
- g_main_loop_quit (data->loop);
- break;
- default:
- break;
- }
- g_free (str);
- print_current_values (data->pipeline);
- return TRUE;
- }
- int main(int argc, charchar *argv[]) {
- CustomData data;
- GstStateChangeReturn ret;
- GIOChannel *io_stdin;
- /* Initialize GStreamer */
- gst_init (&argc, &argv);
- /* Initialize our data structure */
- memset (&data, 0, sizeof (data));
- /* Print usage map */
- g_print (
- "USAGE: Choose one of the following options, then press enter:\n"
- " 'C' to increase contrast, 'c' to decrease contrast\n"
- " 'B' to increase brightness, 'b' to decrease brightness\n"
- " 'H' to increase hue, 'h' to decrease hue\n"
- " 'S' to increase saturation, 's' to decrease saturation\n"
- " 'Q' to quit\n");
- /* Build the pipeline */
- data.pipeline = gst_parse_launch ("playbin2 uri=http://docs.gstreamer.com/media/sintel_trailer-480p.webm", NULL);
- /* Add a keyboard watch so we get notified of keystrokes */
- #ifdef _WIN32
- io_stdin = g_io_channel_win32_new_fd (fileno (stdin));
- #else
- io_stdin = g_io_channel_unix_new (fileno (stdin));
- #endif
- g_io_add_watch (io_stdin, G_IO_IN, (GIOFunc)handle_keyboard, &data);
- /* Start playing */
- 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;
- }
- print_current_values (data.pipeline);
- /* Create a GLib Main Loop and set it to run */
- data.loop = g_main_loop_new (NULL, FALSE);
- g_main_loop_run (data.loop);
- /* Free resources */
- g_main_loop_unref (data.loop);
- g_io_channel_unref (io_stdin);
- gst_element_set_state (data.pipeline, GST_STATE_NULL);
- gst_object_unref (data.pipeline);
- return 0;
- }
工作流程
main()函数非常的简单。用一个playbin2的建立pipeline,注册一个键盘处理函数来监控按键。
- /* Output the current values of all Color Balance channels */
- static void print_current_values (GstElement *pipeline) {
- const GList *channels, *l;
- /* Output Color Balance values */
- channels = gst_color_balance_list_channels (GST_COLOR_BALANCE (pipeline));
- for (l = channels; l != NULL; l = l->next) {
- GstColorBalanceChannel *channel = (GstColorBalanceChannel *)l->data;
- gint value = gst_color_balance_get_value (GST_COLOR_BALANCE (pipeline), channel);
- g_print ("%s: %3d%% ", channel->label,
- 1100 * (value - channel->min_value) / (channel->max_value - channel->min_value));
- }
- g_print ("\n");
- }
这个方法展示了如何获得通道的列表并打印所有通道当前的值。这是通过gst_color_balance_list_channels()方法来实现的,它会返回一个GList结构,我们遍历这个结构即可。
在这个列表里面的每一个element都是GstColorBalanceChannel结构,包括通道名,最小值和最大值。然后就可以在每个通道调用gst_color_balance_get_value()方法来获得当前值。
在这个例子中,当前值常常用占最大值的百分比来显示。
- /* Process a color balance command */
- static void update_color_channel (const gchar *channel_name, gboolean increase, GstColorBalance *cb) {
- gdouble step;
- gint value;
- GstColorBalanceChannel *channel = NULL;
- const GList *channels, *l;
- /* Retrieve the list of channels and locate the requested one */
- channels = gst_color_balance_list_channels (cb);
- for (l = channels; l != NULL; l = l->next) {
- GstColorBalanceChannel *tmp = (GstColorBalanceChannel *)l->data;
- if (g_strrstr (tmp->label, channel_name)) {
- channel = tmp;
- break;
- }
- }
- if (!channel)
- return;
这个方法通过指定通道名来确定通道,然后根据操作增加或者减少值。另外,通道列表的获得后是根据指定的名字来解析获得通道的。很显然,这个列表只应该解析一次,指向通道的指针需要保持在比一个字符串更高效的数据结构中。
- /* Change the channel's value */
- step = 0.1 * (channel->max_value - channel->min_value);
- value = gst_color_balance_get_value (cb, channel);
- if (increase) {
- value = (gint)(value + step);
- if (value > channel->max_value)
- value = channel->max_value;
- } else {
- value = (gint)(value - step);
- if (value < channel->min_value)
- value = channel->min_value;
- }
- gst_color_balance_set_value (cb, channel, value);
然后就获得当前通道的值,修改它但确保它的值有效,使用gst_color_balance_set_value()来设置。
其它没有什么了。运行一下这个程序实际看一下效果。