Bi-directional Predicted Frames/slices (B-frames/slices)
- Require the prior decoding of other frame(s) to be decoded.
- May contain both image data and motion vector displacements or combinations of the two.
- Include some prediction modes that form a prediction of a motion region (e.g., a macroblock or a smaller area) by averaging the predictions obtained using two different previously decoded reference regions.
- In older standard designs (such as MPEG-2), B-frames are never used as references for the prediction of other pictures. As a result, a lower quality encoding (resulting in the use of fewer bits than would otherwise be the case) can be used for such B-frames because the loss of detail will not harm the prediction quality for subsequent pictures.
- In H.264, may or may not be used as references for the decoding of other pictures (at the discretion of the encoder).
- In older standard designs (such as MPEG-2), use exactly two previously decoded pictures as references during decoding, and require one of those pictures to precede the B-frame in display order and the other one to follow it.
- In H.264, can use one, two, or more than two previously decoded pictures as references during decoding, and can have any arbitrary display-order relationship relative to the picture(s) used for its prediction.
- Typically require fewer bits for encoding than either I or P-frames.
Read more about this topic: Video Compression Picture Types
Famous quotes containing the words predicted, frames and/or slices:
“School success is not predicted by a child’s fund of facts or a precocious ability to read as much as by emotional and social measures; being self-assured and interested: knowing what kind of behavior is expected and how to rein in the impulse to misbehave; being able to wait, to follow directions, and to turn to teachers for help; and expressing needs while getting along with other children.”
—Daniel Goleman (20th century)
“In frames as large as rooms that face all ways
And block the ends of streets with giant loaves,
Screen graves with custard, cover slums with praise
Of motor-oil and cuts of salmon, shine
Perpetually these sharply-pictured groves
Of how life should be.”
—Philip Larkin (1922–1986)
“the future is simply nothing at all. Nothing has happened to the present by becoming past except that fresh slices of existence have been added to the total history of the world. The past is thus as real as the present.”
—Charlie Dunbar Broad (1887–1971)