docs: interlaced video: small additions for alternate interlacing

Clarify that width/height in caps is still the frame height/width,
not field height width, just like framerate is frame rate not
field rate.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1465>

diff --git a/subprojects/gst-docs/markdown/additional/design/interlaced-video.md b/subprojects/gst-docs/markdown/additional/design/interlaced-video.md
index bc0886d..5125804 100644 (file)
--- a/subprojects/gst-docs/markdown/additional/design/interlaced-video.md
+++ b/subprojects/gst-docs/markdown/additional/design/interlaced-video.md
@@ -119,5 +119,9 @@ Caps for this interlace mode must also carry a `format:Interlaced` caps feature
 (`GST_CAPS_FEATURE_FORMAT_INTERLACED`) to ensure backwards compatibility for
 the new mode.
 
-The frame rate in the caps still signals the frame rate, so the notional field
+The frame rate in the caps still signals the *frame* rate, so the notional *field*
 rate will be twice the frame rate from the caps (see `GST_VIDEO_INFO_FIELD_RATE_N`).
+
+In the same vein the width and height in the caps will indicate *frame*
+dimensions not field dimensions, meaning the height of the video data inside
+the buffers (1 field) will be half of the height in the caps.

diff --git a/subprojects/gst-docs/markdown/additional/design/mediatype-video-raw.md b/subprojects/gst-docs/markdown/additional/design/mediatype-video-raw.md
index f638ad6..b5347a0 100644 (file)
--- a/subprojects/gst-docs/markdown/additional/design/mediatype-video-raw.md
+++ b/subprojects/gst-docs/markdown/additional/design/mediatype-video-raw.md
@@ -43,7 +43,10 @@
      bottom field (`GST_VIDEO_BUFFER_FLAG_BOTTOM_FIELD`). Top and bottom fields
      are expected to alternate in this mode. Caps for this interlace mode must
      also carry a `format:Interlaced` caps feature (`GST_CAPS_FEATURE_FORMAT_INTERLACED`)
-     to ensure backwards compatibility for the new mode (Since: 1.16)
+     to ensure backwards compatibility for the new mode. `width` and `height`
+     fields in caps indicate **frame** dimensions not field dimensions, meaning
+     the height of the video data inside the buffers will be half of the height
+     in the caps. (Since: 1.16)
 
  - **chroma-site**, `G_TYPE_STRING`: Default `GST_VIDEO_CHROMA_SITE_UNKNOWN`.
    The chroma siting of the video frames.