mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-12-28 11:10:37 +00:00
101 lines
3.3 KiB
Text
101 lines
3.3 KiB
Text
** outdated **
|
|
|
|
Interlaced Video
|
|
================
|
|
|
|
Video buffers have a number of states identifiable through a combination of caps
|
|
and buffer flags.
|
|
|
|
Possible states:
|
|
- Progressive
|
|
- Interlaced
|
|
- Plain
|
|
- One field
|
|
- Two fields
|
|
- Three fields - this should be a progressive buffer with a repeated 'first'
|
|
field that can be used for telecine pulldown
|
|
- Telecine
|
|
- One field
|
|
- Two fields
|
|
- Progressive
|
|
- Interlaced (a.k.a. 'mixed'; the fields are from different frames)
|
|
- Three fields - this should be a progressive buffer with a repeated 'first'
|
|
field that can be used for telecine pulldown
|
|
|
|
Note: it can be seen that the different between the plain interlaced and
|
|
telecine states is that in the telecine state, buffers containing two fields may
|
|
be progressive.
|
|
|
|
Tools for identification:
|
|
- Caps
|
|
- interlaced - boolean
|
|
- interlacing-method - string - "unknown"/"telecine"
|
|
- Flags - GST_VIDEO_BUFFER_...
|
|
- TFF
|
|
- RFF
|
|
- ONEFIELD
|
|
- PROGRESSIVE
|
|
|
|
|
|
Identification of Buffer States
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Note that flags are not necessarily interpreted in the same way for all
|
|
different states nor are they necessarily required nor make sense in all cases.
|
|
|
|
|
|
Progressive
|
|
...........
|
|
|
|
If the caps have no interlaced field, or have interlaced=false, then the buffer
|
|
is progressive. Note the possibility for progressive buffers in telecine streams
|
|
as well.
|
|
|
|
|
|
Plain Interlaced
|
|
................
|
|
|
|
If the caps have interlaced=true and either do not contain the
|
|
interlacing-method field or contain interlacing-method=unknown, then the buffer
|
|
is plain interlaced.
|
|
|
|
GST_VIDEO_BUFFER_TFF indicates whether the top or bottom field is to be
|
|
displayed first. The timestamp on the buffer corresponds to the first field.
|
|
(FIXME - is the duration of the buffer the duration of both fields; each field's
|
|
duration is half the buffer duration)
|
|
|
|
GST_VIDEO_BUFFER_RFF indicates that the first field (indicated by the TFF flag)
|
|
should be repeated. This is generally only used for telecine purposes but as the
|
|
telecine state was added long after the interlaced state was added and defined,
|
|
this flag remains valid for plain interlaced buffers.
|
|
|
|
GST_VIDEO_BUFFER_ONEFIELD means that only the field indicated through the TFF
|
|
flag is to be used. The other field should be ignored.
|
|
|
|
|
|
Telecine
|
|
........
|
|
|
|
If the caps have interlaced=true and interlacing-method=telecine then the
|
|
buffers are in some form of telecine state.
|
|
|
|
The TFF and ONEFIELD flags have the same semantics as for the plain interlaced
|
|
state.
|
|
|
|
GST_VIDEO_BUFFER_RFF in the telecine state indicates that the buffer contains
|
|
only repeated fields that are present in other buffers and are as such
|
|
unneeded. For example, in a sequence of three telecined frames, we might have:
|
|
|
|
AtAb AtBb BtBb
|
|
|
|
In this situation, we only need the first and third buffers as the second
|
|
buffer contains fields present in the first and third.
|
|
|
|
The telecine state require one additional flag to be able to identify
|
|
progressive buffers.
|
|
|
|
GST_VIDEO_BUFFER_PROGRESSIVE means that the buffer containing two fields is a
|
|
progressive frame. The implication is that if this flag is not set, the buffer
|
|
is an 'interlaced' or 'mixed' buffer that contains two fields that, when
|
|
combined with fields from adjacent buffers, allow reconstruction of progressive
|
|
frames.
|