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88 lines
2.9 KiB
Text
88 lines
2.9 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 different 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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- interlaced - boolean
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- interlacing-method - string - "unknown"/"telecine"
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- Flags - GST_VIDEO_BUFFER_...
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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 interlaced field, or have interlaced=false, then the buffer
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is progressive. Note the possibility for progressive buffers in telecine streams
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as well.
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Plain Interlaced
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................
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If the caps have interlaced=true and either do not contain the
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interlacing-method field or contain interlacing-method=unknown, then the buffer
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is plain interlaced.
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GST_VIDEO_BUFFER_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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(FIXME - is the duration of the buffer the duration of both fields; each field's
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duration is half the buffer duration)
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GST_VIDEO_BUFFER_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_BUFFER_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 interlaced=true and interlacing-method=telecine then the
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buffers are in some form of telecine state.
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The TFF, RFF and ONEFIELD flags have the same semantics as for the plain
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interlaced state, however, for the telecine state require one additional flag to
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be able to identify progressive buffers.
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GST_VIDEO_BUFFER_PROGRESSIVE means that the buffer containing two fields is a
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progressive frame. The implication is that if this flag is not set, the buffer
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is an 'interlaced' or 'mixed' buffer that contains two fields that, when
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combined with fields from adjacent buffers, allow reconstruction of progressive
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frames.
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