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design: document new "alternate" video interlace mode

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Tim-Philipp Müller 2019-01-06 15:45:38 +00:00
parent ba2cddfc17
commit 28e10fef5c
2 changed files with 30 additions and 1 deletions
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21
markdown/design/interlaced-video.md
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@ -100,3 +100,24 @@ For example in the following sequence, the third buffer would be mixed
(yes, it is a strange pattern, but it can happen):
AtAb AtBb BtCb CtDb DtDb
### Alternate fields
Since: 1.16
If the video info interlace mode is **"alternate"**, then each buffer
carries a single field of interlaced video.
`GST_VIDEO_BUFFER_FLAG_TOP_FIELD` and `GST_VIDEO_BUFFER_FLAG_BOTTOM_FIELD`
indicate whether the buffer carries a top or bottom field. The order of
buffers/fields in the stream and the timestamps on the buffers indicate the
temporal order of the fields.
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.
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`).

10
markdown/design/mediatype-video-raw.md
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@ -18,7 +18,8 @@
view. use the frame id to get access to the different views.
- **interlace-mode**, `G_TYPE_STRING`: Default progressive. The interlace
mode. The following values are possible:
mode (also see the [interlaced video design docs](design/interlaced-video.md)).
The following values are possible:
- *"progressive"*: all frames are progressive
@ -37,6 +38,13 @@
must be prepared for this. This mode requires multiple
GstVideoMeta metadata to describe the fields.
- *"alternate"*: one field per buffer, with buffer flags indicating
whether the field is the top field (`GST_VIDEO_BUFFER_FLAG_TOP_FIELD`) or
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)
- **chroma-site**, `G_TYPE_STRING`: Default `GST_VIDEO_CHROMA_SITE_UNKNOWN`.
The chroma siting of the video frames.