Game Development Reference
In-Depth Information
as one in decoding, but it can be different from display order, which is related with
the picture coding type. In AVS2, four types of pictures are defined:
•
Intra picture (I-picture): only intra prediction is used in the picture.
•
Forward inter picture (P-picture): both intra prediction and inter prediction can be
used, but only forward prediction is used in inter prediction.
•
Bidirectional decoded picture (B-picture): both intra and inter prediction can be
used, and both forward and backward prediction can be used in inter prediction.
•
Biprediction picture (F-picture): both intra prediction and inter prediction can be
used, but two forward prediction can be used in inter prediction.
•
Intra decoded output background picture (G-picture): only intra prediction is used
in the picture, and it can be used as a long-term reference.
•
Intra decoded non-output background picture (GB-picture): similar to G picture,
but it is only used as a long-term reference and not output for display.
•
Background predictive forward inter decoded picture (S-picture): a picture using
forward prediction from a G picture.
In the sequence, the first picture after a sequence header should be I-picture, and
the first P-picture after a sequence header should use pictures after the sequence
header for forward prediction. When the bitstream does not contain coded B-picture,
the decoding order of pictures is the same as the display order. When B-picture is
present, the decoding order is different from the display order. The decoded pictures
should be reordered according to the following rules:
•
If the current decoded picture is a B-picture, output the current decoded picture
directly.
•
If the current decoded picture is I, G, S or P picture, output the previous decoded
I, S or P picture if it existed; output the previous decoded G-picture if it existed
and it should be output; no picture is outputted if it did not.
Table 3.2
Types and values of start codes
Start code type
Start code value (Hexadecimal)
00 8F blocks
slice_start_code
video_sequence_start_code
B0
video_sequence_end_code
B1
user_data_start_code
B2
i_picture_start_code
B3
reserved
B4
extension_start_code
B5
pbf_picture_start_code
B6
video_edit_code
B7
reserved
90
∼
AF
System start code
B9
∼
FF
