Editing Advanced Video Coding (section)

=== Decoded picture buffering ===
Previously encoded pictures are used by H.264/AVC encoders to provide predictions of the values of samples in other pictures. This allows the encoder to make efficient decisions on the best way to encode a given picture. At the decoder, such pictures are stored in a virtual ''decoded picture buffer'' (DPB). The maximum capacity of the DPB, in units of frames (or pairs of fields), as shown in parentheses in the right column of the table above, can be computed as follows:

: {{mono|''DpbCapacity'' {{=}} min(floor(''MaxDpbMbs'' / (''PicWidthInMbs'' * ''FrameHeightInMbs'')), 16)}}

Where {{mono|''MaxDpbMbs''}} is a constant value provided in the table below as a function of level number, and {{mono|''PicWidthInMbs''}} and {{mono|''FrameHeightInMbs''}} are the picture width and frame height for the coded video data, expressed in units of macroblocks (rounded up to integer values and accounting for cropping and macroblock pairing when applicable). This formula is specified in sections A.3.1.h and A.3.2.f of the 2017 edition of the standard.<ref name=AVC13April2017ITURecommendations/>

<div style="overflow-x:auto">
{| class="wikitable" style="text-align:center;width:800px;"
|-
! Level
| '''1'''
| '''1b'''
| '''1.1'''
| '''1.2'''
| '''1.3'''
| '''2'''
| '''2.1'''
| '''2.2'''
| '''3'''
| '''3.1'''
| '''3.2'''
| '''4'''
| '''4.1'''
| '''4.2'''
| '''5'''
| '''5.1'''
| '''5.2'''
| '''6'''
| '''6.1'''
| '''6.2'''
|-
! {{mono|MaxDpbMbs}}
| 396
| 396
| 900
| 2,376
| 2,376
| 2,376
| 4,752
| 8,100
| 8,100
| 18,000
| 20,480
| 32,768
| 32,768
| 34,816
| 110,400
| 184,320
| 184,320
| 696,320
| 696,320
| 696,320
|}</div>

For example, for an HDTV picture that is 1,920 samples wide ({{samp|1=PicWidthInMbs = 120}}) and 1,080 samples high ({{samp|1=FrameHeightInMbs = 68}}), a Level 4 decoder has a maximum DPB storage capacity of {{samp|floor(32768/(120*68))}} = 4 frames (or 8 fields). Thus, the value 4 is shown in parentheses in the table above in the right column of the row for Level 4 with the frame size 1920×1080.

The current picture being decoded is ''not included'' in the computation of DPB fullness (unless the encoder has indicated for it to be stored for use as a reference for decoding other pictures or for delayed output timing). Thus, a decoder needs to actually have sufficient memory to handle (at least) one frame ''more'' than the maximum capacity of the DPB as calculated above.