View source for GStreamer Debugging

{{#seo:
|title=GStreamer Debugging 
|title_mode=replace
|description={{{description|This Wiki guide from RidgeRun provides a very useful information about the GStreamer Debugging with different debugging approaches.}}}
}}

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== GStreamer debugging approaches ==

Some of these GStreamer debugging approaches are only useful when you are running a pipeline and audio and/or video stops at an unexpected place in the data stream.

=== Use standard GStreamer debug output with filter ===

To see what debug can be enabled, add <tt>--gst-debug-help</tt> to your GStreamer application arguments, such as:

<syntaxhighlight lang="bash">
gst-launch --gst-debug-help
</syntaxhighlight>

Then you can see which debug you are interested in, such as reference counting and buffer movement, and enable all debug output (level output 5).

<syntaxhighlight lang="bash">
gst-launch videotestsrc num-buffers=3 ! fakesink --gst-debug=GST_REFCOUNTING:5,GST_BUFFER:5 --gst-debug-no-color=1  2>&1 | grep "\->0" > log.txt
</syntaxhighlight>

Gets useful data, but typically slows pipeline performance to the point of being not usable.

Another way you can generate the same output is set the <tt>GST_DEBUG</tt> shell variable:

<syntaxhighlight lang="bash">
GST_DEBUG=GST_REFCOUNTING:5 gst-launch videotestsrc num-buffers=3 ! fakesink
</syntaxhighlight>

Here is a simple way to count the number of frames in a (h264/quicktime) video file:

<syntaxhighlight lang="bash">
MOVIE=slomo_1425510055_2.mov
gst-launch -v filesrc location=$MOVIE ! qtdemux ! ffdec_h264 ! fakesink | fgrep chain | wc -l
</syntaxhighlight>

==== The GStreamer debugging levels include: ====
<!-------------------
{| border=2
| 0 || style="text-align:center" | none || No debug information is output.
|-
| 1 || style="text-align:center; background:black; color:red" | 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 || style="text-align:center; background:black; color:yellow" | WARNING || Logs all warnings. Typically these are non-fatal, but user-visible problems are expected to happen.
|-
| 3 || style="text-align:center; background:black; color:green" | 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.
|-
| 4 || style="text-align:center; background:black; color:aqua" | 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, and change of parameters, ...
|-
| 5 || style="text-align:center; background:black; color:gray" | 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.
|-
| 9 || style="text-align:center" | buffer<br>dump || Hex dump of buffer contents.
|}
------------->

{{GStreamer Debugging Levels}}

==== Resolving erroneous pipeline could not link ====

If you get an error like:

 WARNING: erroneous pipeline: could not link capsfilter0 to ffenc_mjpeg0

That means the two elements couldn't exchange GStreamer buffers because they couldn't find a common format they both support. To get an insight on what formats are supported, you can add

  --gst-debug=GST_CAPS:4

=== Create DOT file to see exact pipeline and capabilities used ===

In order to generate a DOT file, set the GST_DEBUG_DUMP_DOT_DIR environment variable to point to the folder where you want the .dot files to be stored.

1) Install "dot" tool on your host machine...to do so simply install graphviz:

<syntaxhighlight lang="bash">
sudo apt-get install graphviz
</syntaxhighlight>

2) On your target board, set the environment dot dump variable:

<syntaxhighlight lang="bash">
export GST_DEBUG_DUMP_DOT_DIR=/root
mkdir -p $GST_DEBUG_DUMP_DOT_DIR
</syntaxhighlight>

3) Run your pipeline, a .dot file will be generated according to each of the state changes that occur showing how the caps are negotiated during the process.

4) Convert the dot files to PNG image files or SVG graphics files

<syntaxhighlight lang="bash">
dot -Tpng input.dot > output.png

dot -Tsvg input.dot > output.svg
</syntaxhighlight>

Using SVG allows you to infinitely zoom to be able to read all the text.  You can use inkscape to view and edit SVG files.

=== Use gst-tracelib library to log key pipeline behavior ===

The gst-tracelib library hooks into GStreamer key functions and logs the function usage behavior.  When the application exits it displays some general statistics. Further analysis can be done based on the data written to the log file. Detailed usage description in the source code [http://cgit.freedesktop.org/~ensonic/gst-tracelib/tree/README README] file.

gst-tracelib logs
* dataflow, messages, queries, and events
* caps set and get activity
* pipeline topology changes
* resource usage

Example usage:

<syntaxhighlight lang="bash">
export GSTTL_HIDE="caps;chk;topo"
export GSTTL_LOG_SIZE=1048576
AV_FILE=/SD/content/MoMen-dm365.mov

LD_PRELOAD=/usr/lib/gst-tracelib/libgsttracelib.so gst-launch filesrc location = $AV_FILE ! qtdemux name=demux ! queue ! dmaidec_h264 numOutputBufs=12 ! \
priority nice=-10 ! queue ! priority nice=-10 ! dmaiperf ! TIDmaiVideoSink accelFrameCopy=true \
videoOutput=DVI videoStd=720P_60 demux.audio_00 ! queue ! priority nice=-5 ! dmaidec_aac ! alsasink
</syntaxhighlight>

By default, the log file is named <tt>/tmp/gsttl.log</tt>. Copy the log file somewhere on your host PC where the scripts gsttl_splitlog.py and gsttl_plt.sh are available (or include the path where the scripts are on $PATH).  You can use the following command to create a png file with the information gathered by gst-tracelib:

 rm -rf gsttl gsttl.png; gsttl_splitlog.py; gsttl_plot.sh | gnuplot; evince gsttl.png

=== Watch system interrupts ===

Run the telnet daemon on the target - likely:

<syntaxhighlight lang="bash">
/etc/init.d/inetd start

# or

inetd
</syntaxhighlight>

telnet into the target hardware and watch the interrupt count

<syntaxhighlight lang="bash">
while sleep 1 ; do cat /proc/interrupts ; done
</syntaxhighlight>

If the pipeline is supposed to be running, the changes in the interrupt count may provide clues as to what is going on.

=== Capturing a core dump ===

If your GStreamer application is crashing with a segfault or similar condition, enable saving a core dump before running the application.

<syntaxhighlight lang="bash">
ulimit -c 100000
mkdir -m 777 /root/dumps
echo "/root/dumps/%e.core" > /proc/sys/kernel/core_pattern
</syntaxhighlight>

Once you have a <tt>/root/dumps/*.core</tt> file, copy it to your workstation and and inspect it with

<syntaxhighlight lang="bash">
ddd  -debugger arm-linux-gnueabi-gdb $GSTREAMER_APPLICATION
</syntaxhighlight>

Then in gdb,

<syntaxhighlight lang="bash">
target core <core file>
bt
</syntaxhighlight>

and see what function caused the core dump.

=== Building application and GStreamer libraries with debug enabled ===

Before using gdb, you need to build your application and the GStreamer libraries with debug enabled.

* Make sure you optimization level is not set to <tt>-O3</tt>
* Add <tt>-ggdb</tt> to your <tt>CFLAGS</tt>
* Remove <tt>-fomit-frame-pointer</tt> flag from <tt>CFLAGS</tt>

For TI DMAI plugin and other gstreamer components in the RidgeRun SDK, the can be done via:

<syntaxhighlight lang="bash">
cd $DEVDIR/proprietary/gst-dmai-plugins
make clean
make APPS_CFLAGS=-ggdb build install
</syntaxhighlight>

=== Use gdb to attach to GStreamer application and examine all the threads ===

The [[Debug and Profiling Guide#Software debugging with GDB | SDK Debugging Guide]] provides detailed instructions.

Built your application with symbols (-g) and no optimization (-O0).  Use GStreamer libraries that are built with symbols.

Attach to your running GStreamer application using gdbserver

<syntaxhighlight lang="bash">
ps
PID=4512 # set the right value based on your application's PID
gdbserver :2345 --attach $PID
</syntaxhighlight>

Then start the cross-compile version of the GNU debugger, like

<syntaxhighlight lang="bash">
arm-linux-gnueabi-gdb -tui $GSTREAMER_APP
</syntaxhighlight>

and get the gdb debugger connected to gdb server on the target

<syntaxhighlight lang="bash">
set solib-absolute-prefix <path to devdir>/fs/fs
file <path to file>
target remote <ip address>:2345
</syntaxhighlight>

List the threads and do a backtrace on each one

<syntaxhighlight lang="bash">
info threads
bt
thread 2
bt
</syntaxhighlight>

=== Use gdbserver in multi-process mode to attach to GStreamer application and examine all the threads ===

If the <tt>info threads</tt> command only shows one thread running, you can see if using gstserver in multi-process mode will work better.

On the target (assuming your program's name is <tt>gstd</tt>), first list the PIDs for all the threads in your application:

<syntaxhighlight lang="bash">
PROG=gstd
ls /proc/`pidof $PROG`/task
</syntaxhighlight>

Then start gdbserver in multi-process mode:

<syntaxhighlight lang="bash">
gdbserver --multi :2345
</syntaxhighlight>

Then on the host start the cross-compile version of the GNU debugger, like

<syntaxhighlight lang="bash">
arm-linux-gnueabi-gdb -tui $GSTREAMER_APP
</syntaxhighlight>

and get the gdb debugger connected to gdb server on the target

<syntaxhighlight lang="bash">
set solib-absolute-prefix <path to devdir>/fs/fs
file <path to file>
target extended-remote <ip address>:2345
</syntaxhighlight>

Now you can attach to a specific PID, do a backtrack, snoop around, and detach from that PID.  Once detached, you can do the same thing again using a different PID from the output of the <tt>ls</tt> command above.

<syntaxhighlight lang="bash">
attach <pid>
bt
detach
</syntaxhighlight>

Once you detach, the PID will run normally.

=== Exit locked GStreamer application and see what works stand-alone ===

If you have a GStreamer application that locks up and doesn't run correctly
even after you exit the program (possibly with Ctrl-C) and restart, then
it is possible some kernel provided resource is the culprit.  For example,
if you are using a defective ALSA audio out driver, you might find the 
GStreamer pipeline locks up in the middle.  If you exit the  GStreamer application
and try a simple audio application, like <tt>aplay</tt>, you might be able 
to identify the source of your problem.

=== Examine history of what transpired just prior to lockup ===

If you have a GStreamer application that locks up and can change the pipeline
to include a (at this point mythical) recent activity history logger, such a
logger element could be put anywhere in the pipeline.  The logger would have 
circular buffers to keep track of all potentially interesting recent history, 
such as pad activity, bus activity, and any other relevant information.  The
circular buffer entries would all be timestamped.  When some event occurs 
(a file exists, a message/signal is received, etc), the element would dump the
history, and continue capturing new data.

This idea is after the pipeline locks up, you could cause the history logger 
to dump its data, and then get an idea of what is supposed to be happening that
isn't occurring.

=== Activate verbose from application ===

Some elements (like fakesink and identity) print out information when you enable the verbose output (running the pipeline through gst-launch with the option -v), in order to activate this output  manually from a C application you can use:

 g_signal_connect( pipeline, "deep-notify", G_CALLBACK( gst_object_default_deep_notify ), NULL );

=== Enable DMAI Davinci Multimedia Application Interface debug output ===

If you are using the TI DMAI GStreamer plug-in for the TI Davinci and OMAP SoCs, then you can enable DMAI debug to get more information if a hardware-accelerated encoder or decoder is throwing an error.

<syntaxhighlight lang="bash">
DMAI_DEBUG=2 gst-launch -e alsasrc num-buffers=50 ! 'audio/x-raw-int,rate=(int)44100,channels=(int)2' ! queue ! dmaienc_aac bitrate=128000 ! qtmux ! filesink location=gstaudio_aac_2ch_128k.mp4
</syntaxhighlight>

=== Enable CE Codec Engine debug output ===

If you are using the TI DMAI GStreamer plug-in for the TI Davinci and OMAP SoCs, then you can enable CE debug to get more information if a hardware-accelerated encoder or decoder is throwing an error.  Note that the stack is GStreamer DMAI plug-in which uses DMAI which uses CE which uses codecs that take advantage of the hardware accelerators.

<syntaxhighlight lang="bash">
CE_DEBUG=3 gst-launch -e alsasrc num-buffers=50 ! 'audio/x-raw-int,rate=(int)44100,channels=(int)2' ! queue ! dmaienc_aac bitrate=128000 ! qtmux ! filesink location=gstaudio_aac_2ch_128k.mp4
</syntaxhighlight>

And you can combine DMAI and CE debug

<syntaxhighlight lang="bash">
CE_DEBUG=3 DMAI_DEBUG=2 gst-launch -e alsasrc num-buffers=50 ! 'audio/x-raw-int,rate=(int)44100,channels=(int)2' ! queue ! dmaienc_aac bitrate=128000 ! qtmux ! filesink location=gstaudio_aac_2ch_128k.mp4
</syntaxhighlight>

To write the debug to a file on tmpfs, which should reduce the performance impact of enabling debug, add 

<syntaxhighlight lang="bash">
2>&1 | cat - > /tmp/gst-debug.txt
</syntaxhighlight>

to the end of the gst-launch command.

=== Use NFS mount to make it easy to transfer files ===

If you are creating files on a network-connected embedded device, you can use NFS mount (which is different than NFS root mount) so that once you generate a file, it is easy to get it on your desktop machine.  For any real-time debugging, don't use NFS root mount as the network activity will affect the timing of your pipelines.  See [[Setting Up A NFS Service]] for instructions on configuring your desktop machine.

<syntaxhighlight lang="bash">
HOST_IP=10.0.1.1
HOST_NFS_SHARE_DIR=/local/home/tfischer/work/sdk/fs/fs

mkdir /tmp/nfs
mount -t nfs -n -o nolock,rsize=1024,wsize=1024 $HOST_IP:$HOST_NFS_SHARE_DIR /tmp/nfs
</syntaxhighlight>

Now you can copy files between host and target over the network.  If you have a file like <tt>/tmp/debug-out.txt</tt> on the target, you can copy it to the $HOST_NFS_SHARE_DIR on the host using

 cp /tmp/debug-out.txt /tmp/nfs

=== Look for memory leaks ===

Looking for memory leaks in programs is a very challenging problem. This is even more true for embedded systems, since some of the best memory analysis tools aren't always available, or are difficult to use in this environment.

An easy way to debug the memory leak of a GStreamer program that is running is by looking at the reference counters.  Memory leaks on GStreamer happened because reference counters on one or more objects never go back to zero.

References:

* [http://www.linuxjournal.com/article/6059 Linux Journal article - Memory Leak Detection in Embedded Systems]

==== GStreamer <tt>GST_REFCOUNTING</tt> Debug Variable ====

One of the debug variables is <tt>GST_REFCOUNTING</tt>.  With that, you can get a log of all the refcount changes that happened inside a gst application.

==== Setting <tt>GST_REFCOUNTING</tt>  ====

Add the following to your application's command line parameters:

<syntaxhighlight lang="bash">
--gst-debug=GST_REFCOUNTING:5
</syntaxhighlight>

Another option is to set the GStreamer debugging shell variable, then run your program:

<syntaxhighlight lang="bash">
export GST_DEBUG=GST_REFCOUNTING:5
</syntaxhighlight>

==== Filtering debug output ====

Here are several examples of how to filter the debug output.

You can see which objects disappear, meaning their reference count reaches zero:

<syntaxhighlight lang="bash">
gst-launch --gst-debug=GST_REFCOUNTING:5 videotestsrc num-buffers=3 ! fakesink 2>&1 | grep "\->0" | cut -d' ' -f 19
</syntaxhighlight>

In useful applications, there are always some objects that aren't freed until the program exists.  With a simple gst-hello example all the objects are always freed.  If you set the pipe to run, let's say 13 times, and in the log, you see one object that wasn't freed and the count reached 13 or more, then you have a suspicious object or if you see that the number of non-freed objects increases as you increase the number of runs, then you have an indication of a problem.

=== Use remote syslog ===

If your application logs warnings and errors, use [[How to Configure Remote Syslog Logging | remote syslog]] to make the information more easily available.

If your application generates output, you can redirect it to Syslog as follows:

<syntaxhighlight lang="bash">
MY_APP=gst-render

$MY_APP | logger -t "$MY_APP:" 
</syntaxhighlight>

=== Generated files debug ===

There are some tools that can be used for getting information from generated files by GStreamer:

*libmp4v2

*MP4BOX

*mediainfo

With MP4Box you can use the -info in order to get more info from a generated mp4 file:
<syntaxhighlight lang="bash">
MP4Box -info test.mp4
</syntaxhighlight>

== GStreamer Element Debugging ==

If you are creating an element you plan to use in an embedded device, you might find it helpful to build and test the element on your development machine first.

<syntaxhighlight lang="bash">
./autogen.sh
CFLAGS=-ggdb ./configure
make
objdump -x src/.libs/*.so | fgrep DEBUG # verify library is built with debugging symbols enabled
</syntaxhighlight>

Use GST_PLUGIN_PATH to enable GStreamer to find your element library:

<syntaxhighlight lang="bash">
export GST_PLUGIN_PATH=$HOME/projects/gst-emboverlay/src/.libs 
gst-inspect emboverlay
</syntaxhighlight>

Test out your element.  Better to use GStreamer daemon than gst-launch.

<syntaxhighlight lang="bash">
TEXT_OVERLAY="text=Hello\ There text-offseth=50 text-offsetv=100 text-font-height=50 text-color=0x800040 text-enable=true"
TEXT2_OVERLAY="text2=World text2-offseth=50 text2-offsetv=150 text2-font-height=50 text2-color=0x800040 text2-enable"
TIME_OVERLAY="time-param=%b\ %d\ %Y\ %H:%M:%S time-offseth=50 time-offsetv=200 time-font-height=50 time-color=0x800040 time-enable=true"
LOGO_OVERLAY="logo=$HOME/projects/gst-emboverlay/RidgeRunLogo312x84-with-alpha-channel.png logo-offseth=-1 logo-offsetv=-1 logo-transp=1 logo-scale=1.0 logo-autofit=true time-enable=true"
FRAME_OVERLAY="frame-number=-20 frame-offseth=50 frame-offsetv=250 frame-font-height=50 frame-color=0x800040 frame-enable=true" 

CAPS="video/x-raw-yuv, format=(fourcc)YV12, width=(int)1280, height=(int)720, interlaced=(boolean)false, pixel-aspect-ratio=(fraction)1/1, framerate=(fraction)10/1"

gst-launch --gst-debug=emboverlay:4 -v v4l2src num-buffers=60 ! capsfilter caps="$CAPS" ! emboverlay $TIME_OVERLAY $TEXT_OVERLAY $TEXT2_OVERLAY $LOGO_OVERLAY $FRAME_OVERLAY ! xvimagesink
</syntaxhighlight>

== GStreamer Performance Tuning ==

This is worthy of its own [[Embedded GStreamer Performance Tuning]] topic.

== GStreamer Application Development ==

=== GStreamer Daemon ===

If you can use [https://github.com/RidgeRun/gstd/wiki GStreamer Daemon] as your streaming media server, then avoid writing a custom application in the first place!

=== Developing on host computer ===

If you have a pipeline where source pads and sink pads are getting connected and disconnected, then you will likely need to write a custom streaming media server.  Most people find it easier to build and debug by running the application on the host before trying it on the target hardware.  

== See also ==
* '''GStreamer Basic tutorial 11: Debugging Tools''' gstreamer.freedesktop.org tutorial documentation.URL: https://gstreamer.freedesktop.org/documentation/tutorials/basic/debugging-tools.html  
* '''Running GStreamer Applications — How to run and debug your GStreamer application''' gstreamer.freedesktop.org documentation. URL: http://www.gstreamer.net/data/doc/gstreamer/head/gstreamer/html/gst-running.html 
* '''Things to check when writing an element''' gstreamer.freedesktop.org plugin development documentation.URL: https://gstreamer.freedesktop.org/documentation/plugin-development/appendix/checklist-element.html 
* '''GstInfo - Debugging and logging facilities''' gstreamer.freedesktop.org GStreamer 1.0 Core Reference Manual.URL: http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/gstreamer-GstInfo.html 
* '''gst-tracelib - Performance tracing library for GStreamer''' GStreamer tracing library.URL: http://cgit.freedesktop.org/~ensonic/gst-tracelib/tree/README
* [[GStreamer_Debugging_Using_GDB |'''GStreamer Debugging Using GDB''']]

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