On behalf of Gopise Yuan.
A collection of several GST debugging tips and known-how.
When you need to play onto a DRM layer/plane directly without going through compositor, kmssink should be a good choice:
// kmssink, with scale and adjust alpha property (opaque) and zpos (this requires kmssink>=1.16):
gst-launch-1.0 filesrc location=/media/AVC-AAC-720P-3M_Alan.mov ! decodebin ! imxvideoconvert_g2d ! kmssink plane-id=37 render-rectangle="<100,100,720,480>" can-scale=false plane-properties=s,alpha=65535,zpos=2
When using playbin, you can still customize the pipeline besides the sink plugin, e.g. add a converter plugin:
// Playbin with additional customization on converter before sink:
gst-launch-1.0 playbin uri=file:///mnt/MP4_H264_AAC_1920x1080.mp4 video-sink="imxvideoconvert_g2d ! video/x-raw,format=BGRA,width=1920,height=1080 ! kmssink plane-id=44"
GST can generate a pipeline graph for analyzing the pipeline in a intuitive manner:
// Generate pipeline graph:
1. Export GST_DEBUG_DUMP_DOT_DIR=<dump-folder>, GST_DEBUG=4
2. Run pipeline with gst-launch or others.
3. Copy all dump files (.dot) from <dump-folder>. Note: one dump file will be created for each state transaction.
Normally, what we need will be PAUSE_READY or READY_PAUSE, after which pipeline has been setup.
4. Convert the .dot file to PDF with Graphviz:
dot -Tpdf 0.00.03.685443250-gst-launch.PAUSED_READY.dot > pipeline_PAUSED_READY.pdf
