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raw [2020/03/29 17:14] – [strides and offsets] yairraw [2024/06/30 17:30] (current) – yair
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 ====GRAY8 vs RTP==== ====GRAY8 vs RTP====
 **problem**: \\ **problem**: \\
-single plane raw formats are not part of [[https://tools.ietf.org/html/rfc4175|rfc4175]], and as such 2nd class citizens to gstreamer, RTSP and [[https://linuxtv.org/downloads/v4l-dvb-apis/uapi/v4l/pixfmt-grey.html|anywhere]]. +single plane raw formats are not part of [[https://tools.ietf.org/html/rfc4175|rfc4175]], and as such 2nd class citizens to gstreamer, RTSP or [[https://www.kernel.org/doc/html/v4.10/media/uapi/v4l/pixfmt-grey.html|anywhere]] else. 
  
 **solution**: \\ **solution**: \\
-map the GRAY8 **one plane** source into a quarter width **four plane** RGBA output image\\ +an image format is **just a convention**, internally they are byte(octet) streams. we can re-package a datastream to another format, as long as we mind our strides.  
-we will then remap it to Y8 on the receiving side. \\ + 
-the trick is to use gstreamer built in forma spec and let it optimize the remapping. +view the image format as just a stream of octets. here is our stream in Y8 format 
 +       +--+--+--+--+ +--+--+--+--+ 
 +       |Y1|xx|xx|xx| |Y1|xx|xx|xx| ... 
 +       +--+--+--+--+ +--+--+--+--+ 
 +and again, data quartered and represented in 8 bit depth and with stride of 4 
 +       +--+--+--+--+ +--+--+--+--+ 
 +       |R0|G0|B0|A0| |R1|G1|B1|A1| ... 
 +       +--+--+--+--+ +--+--+--+--+ 
 + 
 +note the above represents two sequential pixels.  
 + 
 +the trick is to use gstreamer built in [[https://gstreamer.freedesktop.org/documentation/additional/design/mediatype-video-raw.html?gi-language=c#formats|format spec]] and let that handle the conventions. 
  
 the [[https://www.collabora.com/news-and-blog/blog/2016/02/16/a-programmers-view-on-digital-images-the-essentials/|hammer]] the [[https://www.collabora.com/news-and-blog/blog/2016/02/16/a-programmers-view-on-digital-images-the-essentials/|hammer]]
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 00000000 (0x7f369c00a8c0): eb eb eb eb eb eb eb eb eb eb eb eb eb eb eb eb  ................ 00000000 (0x7f369c00a8c0): eb eb eb eb eb eb eb eb eb eb eb eb eb eb eb eb  ................
 00000000 (0x556228700560): eb eb eb eb eb eb eb eb eb eb eb eb eb eb eb eb  ................ 00000000 (0x556228700560): eb eb eb eb eb eb eb eb eb eb eb eb eb eb eb eb  ................
-┌────────┬─────────────────────────┬─────────────────────────┬────────┬────────┐ 
-│00000000│ eb eb eb eb eb eb eb eb ┊ eb eb eb eb eb eb eb eb │××××××××┊××××××××│ 
-└────────┴─────────────────────────┴─────────────────────────┴────────┴────────┘ 
 </code> </code>
 **note**: why white pixel is not FF=(255)?\\ **note**: why white pixel is not FF=(255)?\\
-gstreamer uses YUV colorimetry when generating a GRAY8 test image and YUV doesnt use the entire 0-255 space. [[https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/issues/738|issue]]+gstreamer uses YUV colorimetry when generating a GRAY8 test image \\ 
 +and YUV doesnt use the entire 0-255 space. [[https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/issues/738|issue]]
  
 +**note2**: this example is running on linux/debian, \\
 +to adapt to windows using powershell replace ''\'' with ''`'' and \\
 +place quotes around  ''video/x-raw, format=GRAY8, width=4, height=4''
  
  
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 </code> </code>
      
- 
-====raw parsing==== 
-<code c> 
-gst-launch-1.0 videotestsrc pattern=white num-buffers=1 \ 
-! video/x-raw, format=GRAY8, width=4, height=4 \ 
-! identity dump=1 \ 
-! filesink location=white.gray8 -q 
- 
-gst-launch-1.0  multifilesrc location=white.gray8 num_buffers=1 \ 
-! rawvideoparse format=rgba width=1 height=4 \ 
-! identity dump=1 \ 
-! filesink location=white.rgba -q 
-</code> 
  
  
 ====strides and offsets==== ====strides and offsets====
  
-we dont need to dig into the following as we use the capabilities as listed in [[https://gstreamer.freedesktop.org/documentation/additional/design/mediatype-video-raw.html?gi-language=c#formats|design document]]. \\ +there are caveats to this approach (yuv). get the hammer and study the [[https://gstreamer.freedesktop.org/documentation/additional/design/mediatype-video-raw.html?gi-language=c#formats|design document]]. 
-but hopefully this section will advance your understanding.+
  
  
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 </hidden> </hidden>
  
-[[https://github.com/torvalds/linux/blob/master/include/uapi/drm/drm_fourcc.h#L174|fourcc]] on linux +[[https://github.com/torvalds/linux/blob/master/include/uapi/drm/drm_fourcc.h#L174|fourcc]] on linux\\ 
 +[[https://docs.microsoft.com/en-us/windows/win32/medfound/image-stride?redirectedfrom=MSDN|MSDN on stride]]