Bug 89660 – [GTK] Add support for graphviz debug output for the gstreamer video pipeline

• Component: WebKitGTK
• Status: RESOLVED FIXED

[Allan Xavier]

GStreamer has a useful debugging feature where it can output a given pipeline to a Graphviz dot file. Having this feature enabled in WebKit would be helpful for debugging development/end user problems with the video pipeline.

Some more information on this feature (along with an example) can be found in the GStreamer SDK documentation http://docs.gstreamer.com/display/GstSDK/Basic+tutorial+11%3A+Debugging+tools

The following patch will output a dot file for errors and state changes in the video pipeline when the environment variable GST_DEBUG_DUMP_DOT_DIR is set. This is similar to how gst-launch implements the same functionality.

[Allan Xavier]

Created attachment 148794 [details]
Patch for supporting graphviz debug output

[Philippe Normand]

Let me know if you need the commit-queue to land this patch.

[Martin Robinson]

Comment on attachment 148794 [details]
Patch for supporting graphviz debug output

View in context: https://bugs.webkit.org/attachment.cgi?id=148794&action=review

> Source/WebCore/platform/graphics/gstreamer/MediaPlayerPrivateGStreamer.cpp:799
> +            // Construct a filename for the graphviz dot file output

Nit: You're missing a period at the end of this sentence.

> Source/WebCore/platform/graphics/gstreamer/MediaPlayerPrivateGStreamer.cpp:801
> +            dotFileName = g_strdup_printf("webkit-video.%s_%s", gst_element_state_get_name(oldState), gst_element_state_get_name(newState));

It's probably better to use 

CString dotFileName = String::format("webkit-video.%s_%s", gst_element_state_get_name(oldState), gst_element_state_get_name(newState)).utf8();

> Source/WebCore/platform/graphics/gstreamer/MediaPlayerPrivateGStreamer.cpp:803
> +            GST_DEBUG_BIN_TO_DOT_FILE_WITH_TS(GST_BIN(m_playBin), GST_DEBUG_GRAPH_SHOW_ALL, dotFileName);

This would become:
GST_DEBUG_BIN_TO_DOT_FILE_WITH_TS(GST_BIN(m_playBin), GST_DEBUG_GRAPH_SHOW_ALL, dotFileName.data());

[Allan Xavier]

Created attachment 148844 [details]
Patch for supporting graphviz debug output

This revised patch has the following changes:

* The improvements recommended by Martin in comment #3.
* The string formatting call is now split onto multiple lines for better readability.
* The pendingState variable has been removed (gst_message_parse_state_changed can handle null arguments).

[WebKit Review Bot]

Comment on attachment 148844 [details]
Patch for supporting graphviz debug output

Clearing flags on attachment: 148844

Committed r121169: <http://trac.webkit.org/changeset/121169>

[WebKit Review Bot]

All reviewed patches have been landed.  Closing bug.