GStreamer 中的 fdsink 元素不能用于 output 正确的字节流到管道

Question

Because I need to output the RTSP stream pulled from the GStreamer command line to my Python program, I use the fdsink element to output the byte-stream from the pipeline. The video can be displayed correctly by using the xvimagesink element. The command line is as follows.

gst-launch-1.0 rtspsrc location=rtsp://wowzaec2demo.streamlock.net/vod/mp4:BigBuckBunny_115k.mp4 ! queue2 ! rtph264depay ! capsfilter caps="video/x-h264, width=240, height=160" ! avdec_h264 ! videoconvert ! xvimagesink

Correct video:

Then I use fdsink instead of the xvimagesink element to output the byte stream from the pipeline and play it with ffplay. It can't display correct video. The command line is as follows.

gst-launch-1.0 rtspsrc location=rtsp://wowzaec2demo.streamlock.net/vod/mp4:BigBuckBunny_115k.mp4 ! queue2 ! rtph264depay ! capsfilter caps="video/x-h264, width=240, height=160" ! avdec_h264 ! videoconvert ! fdsink | ffplay -f rawvideo -pixel_format rgb24 -video_size 240*160 -i -

Wrong video:

So is fdsink element wrong or other elements wrong? Thank you for taking the time to help me solve the problem

Answer 1

There are two issues:

• GStreamer writes text messages to stdout , and FFplay interprets the text as raw pixels.
  Add --quiet to prevent GStreamer from writing text to stdout .

• Default GStreamer raw video format is "planar RGB" - red plain then green plane then blue plane.
  We may convert pixel format to data ordered BGR (b,g,r,b,g,r...) by adding:
  capsfilter caps="video/x-raw, format=BGR"

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The following command plays well in my machine:

gst-launch-1.0 --quiet rtspsrc location=rtsp://wowzaec2demo.streamlock.net/vod/mp4:BigBuckBunny_115k.mp4, queue2, rtph264depay, capsfilter caps="video/x-h264, width=240, height=160" ! avdec_h264 ! videoconvert ! capsfilter caps="video/x-raw, format=BGR" ! fdsink | ffplay -f rawvideo -pixel_format rgb24 -video_size 240x160 -i -

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It also works without capsfilter caps="video/x-h264, width=240, height=160" :

gst-launch-1.0 --quiet rtspsrc location=rtsp://wowzaec2demo.streamlock.net/vod/mp4:BigBuckBunny_115k.mp4, queue2 ! rtph264depay ! avdec_h264 ! videoconvert ! capsfilter caps="video/x-raw, format=BGR" ! fdsink | ffplay -f rawvideo -pixel_format rgb24 -video_size 240x160 -i -