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97 lines
3.2 KiB
Text
97 lines
3.2 KiB
Text
Interlaced Video
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================
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Video buffers have a number of states identifiable through a combination of caps
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and buffer flags.
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Possible states:
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- Progressive
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- Interlaced
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- Plain
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- One field
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- Two fields
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- Three fields - this should be a progressive buffer with a repeated 'first'
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field that can be used for telecine pulldown
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- Telecine
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- One field
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- Two fields
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- Progressive
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- Interlaced (a.k.a. 'mixed'; the fields are from different frames)
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- Three fields - this should be a progressive buffer with a repeated 'first'
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field that can be used for telecine pulldown
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Note: It can be seen that the difference between the plain interlaced and
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telecine states is that in the telecine state, buffers containing two fields may
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be progressive.
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Tools for identification:
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- Caps
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- interlace-mode - string - "progressive"/"interleaved"/"mixed"
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- Flags - GST_VIDEO_FLAG_...
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- TFF
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- RFF
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- ONEFIELD
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- PROGRESSIVE
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Identification of Buffer States
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Note that flags are not necessarily interpreted in the same way for all
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different states nor are they necessarily required nor make sense in all cases.
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Progressive
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...........
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If the caps have no interlace-mode field on a source pad, or have
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interlace-mode="progressive", then the buffer is progressive. The lack of the
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interlace-mode field on a sink pad means that the element is not concerned
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about the mode and can handle all. Note the possibility for progressive buffers
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in telecine streams as well.
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Plain Interlaced
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................
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If the caps have interlace-mode="interleaved" or "fields", then the buffer is
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plain interlaced.
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GST_VIDEO_FLAG_TFF indicates whether the top or bottom field is to be
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displayed first. The timestamp on the buffer corresponds to the first field.
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GST_VIDEO_FLAG_RFF indicates that the first field (indicated by the TFF flag)
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should be repeated. This is generally only used for telecine purposes but as the
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telecine state was added long after the interlaced state was added and defined,
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this flag remains valid for plain interlaced buffers.
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GST_VIDEO_FLAG_ONEFIELD means that only the field indicated through the TFF
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flag is to be used. The other field should be ignored.
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Telecine
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........
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If the caps have interlace-mode=mixed then the buffers are in some form of
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telecine state.
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The TFF and ONEFIELD flags have the same semantics as for the plain interlaced
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state.
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GST_VIDEO_FLAG_RFF in the telecine state indicates that the buffer contains
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only repeated fields that are present in other buffers and are as such
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unneeded. For example, in a sequence of three telecined frames, we might have:
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AtAb AtBb BtBb
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In this situation, we only need the first and third buffers as the second
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buffer contains fields present in the first and third.
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The telecine state requires one additional flag to be able to identify
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progressive buffers.
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The presence of the GST_VIDEO_FLAG_INTERLACED means that the buffer is an
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'interlaced' or 'mixed' buffer that contains two fields that, when combined
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with fields from adjacent buffers, allow reconstruction of progressive frames.
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The absence of the flag implies the buffer containing two fields is a
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progressive frame.
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