Basic tutorial

element -> pad -> caps 包含关系

Basic tutorial 7: Multithreading and Pad Availability

Request pads

To request (or release) pads in the PLAYING or PAUSED states, you need to take additional cautions (Pad blocking) which are not described in this tutorial. It is safe to request (or release) pads in the NULL or READY states, though.

多管道播放

单播放
gst-launch-1.0 filesrc location=/home/xuleilx/Music/123.mp3 ! decodebin ! autoaudiosink
单显示
gst-launch-1.0 filesrc location=/home/xuleilx/Music/123.mp3 ! decodebin ! wavescope ! videoconvert ! autovideosink
播放+显示
gst-launch-1.0 filesrc location=/home/xuleilx/Music/123.mp3 ! decodebin ! tee name=t ! queue ! autoaudiosink t. ! queue ! wavescope ! videoconvert ! autovideosink
修改显示范围，增加个capsfilter
gst-launch-1.0 filesrc location=/home/xuleilx/Music/123.mp3 ! decodebin ! tee name=t ! queue ! autoaudiosink t. ! queue ! wavescope ! capsfilter caps=”video/x-raw, format=BGRx,width=1280, height=720, framerate=30/1” ! videoconvert ! autovideosink

注意：
playbin的flags的vis有类似功能

Basic tutorial 8: Short-cutting the pipeline

主要通过appsrc，appsink实现，截取管道中的数据。

This tutorial expands Basic tutorial 7: Multithreading and Pad Availability in two ways: firstly, the audiotestsrc is replaced by an appsrc that will generate the audio data. Secondly, a new branch is added to the tee so data going into the audio sink and the wave display is also replicated into an appsink. The appsink uploads the information back into the application, which then just notifies the user that data has been received, but it could obviously perform more complex tasks.

Basic tutorial 10: GStreamer tools

三大利器，可以参照其源码实现想要的功能

1
2
3

gst-launch-1.0
gst-inspect-1.0
gst-discoverer-1.0 # id3信息

Basic tutorial 11: Debugging tools

Printing debug information

The debug log

The first category is the Debug Level, which is a number specifying the amount of desired output:

| # | Name    | Description                                                    |
|---|---------|----------------------------------------------------------------|
| 0 | none    | No debug information is output.                                |
| 1 | ERROR   | Logs all fatal errors. These are errors that do not allow the  |
|   |         | core or elements to perform the requested action. The          |
|   |         | application can still recover if programmed to handle the      |
|   |         | conditions that triggered the error.                           |
| 2 | WARNING | Logs all warnings. Typically these are non-fatal, but          |
|   |         | user-visible problems are expected to happen.                  |
| 3 | FIXME   | Logs all "fixme" messages. Those typically that a codepath that|
|   |         | is known to be incomplete has been triggered. It may work in   |
|   |         | most cases, but may cause problems in specific instances.      |
| 4 | INFO    | Logs all informational messages. These are typically used for  |
|   |         | events in the system that only happen once, or are important   |
|   |         | and rare enough to be logged at this level.                    |
| 5 | DEBUG   | Logs all debug messages. These are general debug messages for  |
|   |         | events that happen only a limited number of times during an    |
|   |         | object's lifetime; these include setup, teardown, change of    |
|   |         | parameters, etc.                                               |
| 6 | LOG     | Logs all log messages. These are messages for events that      |
|   |         | happen repeatedly during an object's lifetime; these include   |
|   |         | streaming and steady-state conditions. This is used for log    |
|   |         | messages that happen on every buffer in an element for example.|
| 7 | TRACE   | Logs all trace messages. Those are message that happen very    |
|   |         | very often. This is for example is each time the reference     |
|   |         | count of a GstMiniObject, such as a GstBuffer or GstEvent, is  |
|   |         | modified.                                                      |
| 9 | MEMDUMP | Logs all memory dump messages. This is the heaviest logging and|
|   |         | may include dumping the content of blocks of memory.           |
+------------------------------------------------------------------------------+

设置插件的日志等级

GST_DEBUG=2,audiotestsrc:6

支持正则表达式

GST_DEBUG=2,audio*:6

显示所有插件的日志等级：

gst-launch-1.0 --gst-debug-help

Gstreamer日志输出文件，默认输出到终端

export GST_DEBUG_FILE=/tmp/gst.log

Adding your own debug information

Use the GST_ERROR(), GST_WARNING(), GST_INFO(), GST_LOG() and GST_DEBUG() macros. They accept the same parameters as printf, and they use the default category (default will be shown as the Debug category in the output log).

Getting pipeline graphs

环境变量

export GST_DEBUG_DUMP_DOT_DIR=/tmp/

代码中

GST_DEBUG_BIN_TO_DOT_FILE(GST_BIN(mypipeline), GST_DEBUG_GRAPH_SHOW_ALL, "test");
生成/tmp/test.dot文件，用vscode安装Graphviz Preview可查看

Basic tutorial 12: Streaming

对于流媒体来说，buffer是通用解决方案。gstreamer提供了queue、queue2和multiqueue

1 2	gst_bus_add_signal_watch (bus); g_signal_connect (bus, "message", G_CALLBACK (cb_message), &data);

Live streams cannot be paused, so they behave in PAUSED state as if they were in the PLAYING state. Setting live streams to PAUSED succeeds, but returns GST_STATE_CHANGE_NO_PREROLL, instead of GST_STATE_CHANGE_SUCCESS to indicate that this is a live stream. We are receiving the NO_PREROLL return code even though we are trying to set the pipeline to PLAYING, because state changes happen progressively (from NULL to READY, to PAUSED and then to PLAYING).

For the second network issue, the loss of clock, we simply set the pipeline to PAUSED and back to PLAYING, so a new clock is selected, waiting for new media chunks to be received if necessary.

Basic tutorial 14: Handy elements

Bins

playbin
uridecodebin
decodebin

File input/output

filesrc
filesink

Network

souphttpsrc

Test media generation

videotestsrc
audiotestsrc

Video adapters

videoconvert
videorate
videoscale

Audio adapters

audioconvert
audioresample
audiorate

Multithreading

queue
queue2
multiqueue
tee

Capabilities

capsfilter
typefind

Debugging

fakesink
identity