Understanding my pipeline - unknown avdec_h264 output format

andis andreas.schimpe at gmail.com
Wed Dec 18 16:40:24 UTC 2019

Hi all, 
I have set up a GStreamer Pipeline in ROS, C++ as follows: 
Sending side: 
- appsrc (is a PTGrey Camera that emits YUV422packed raw images that I push
to the pipeline)
- capsfilter
- videoconvert
- x264enc
- rtph264pay
- udpsink

Receiving side: 
- udpsrc
- rtph264depay
- avdec_h264
- videoconvert
- xvimagesink

This pipeline works well, and I can have my video feed being displayed by
the xvimagesink. 

However, I actually want have the raw/decoded image frames at the end of the
receiving side again. My camera is publishing at a resolution of 1936x1464
px. In the YUV422packed color space (that is the GStreamer UYVY video
format) I have 2 Byte/px. Thus, I am pushing a buffer of size 5,668,608
Bytes into the pipeline. 

Now I attached identity modules to my receiving side, and I get buffers of
size 6,172,672 Bytes (larger than the raw image) after the avdec_h264 and of
size 4,251,456 Bytes (smaller than the raw image) after the videoconvert
before the xvimagesink. I assume there is some metadata in the buffers. How
can i receive the raw, decoded image frames (of size 5,668,608 in the UYVY
video format) from these buffers again? 


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