Fix a few TODOs in the encoder guide.
Added a figure and changed some logics that recently changed.
Removed a few refs that are not necessary.
Change-Id: I234107188a2ceb069e625bad6e3316000d3cd347
diff --git a/doc/dev_guide/av1_encoder.dox b/doc/dev_guide/av1_encoder.dox
index e18c73f..81ebadc 100644
--- a/doc/dev_guide/av1_encoder.dox
+++ b/doc/dev_guide/av1_encoder.dox
@@ -806,9 +806,9 @@
</ul>
Except for the first trivial case where there is no prior knowledge of the
-following frames, the function \ref calculate_gf_length() tries to
-determine the GF group length based on the first pass statistics. As shown
-in figure [TODO BohalLi@], the determination is divided into two parts:
+following frames, the function \ref calculate_gf_length() tries to determine the
+GF group length based on the first pass statistics. The determination is divided
+into two parts:
<ol>
<li>Baseline decision based on accumulated statistics: this part of the function
@@ -820,11 +820,10 @@
first-pass statistics, the baseline decision is set at the current point.</li>
<li>If we are not at the end of the first-pass statistics, the next part will
- try to refine the baseline decision. The algorithm is based on
- \ref FIRSTPASS_STATS.coded_error. It tries to label the frames in the
- baseline group into two classes: high-error and low-error, and cuts the GF
- group at the furthest location that is also of the low-error class.
- Detailed algorithm description is introduced here [TODO].</li>
+ try to refine the baseline decision. This algorithm is based on the analysis
+ of firstpass stats. It tries to cut the groups in stable regions or
+ relatively stable points. Also it tries to avoid cutting in a blending
+ region.</li>
</ol>
As mentioned, for two-pass encoding, the function \ref
@@ -846,7 +845,9 @@
\ref calculate_gf_length() is called again with the updated maximum
length, and it only sets the length for a single GF group
(\ref RATE_CONTROL.intervals_till_gf_calculate_due is set to 1). This process
-is shown in [TODO BohalLi@].
+is shown below.
+
+\image html tplgfgroupdiagram.png "" width=40%
Before encoding each frame, the encoder checks
\ref RATE_CONTROL.frames_till_gf_update_due. If it is zero, indicating
@@ -863,40 +864,39 @@
as other GF group level parameters (e.g. bit allocation) once the length of
the current GF group is determined.
-The function first iterates through the first pass statistics in the GF group
-to accumulate various stats, using (TODO REF) accumulate_this_frame_stats()
-and (TODO REF)accumulate_next_frame_stats(). The accumulated statistics are
-then used to determine the use of the use of ALTREF frame along with other
-properties of the GF group. The values of \ref RATE_CONTROL.cur_gf_index,
-\ref RATE_CONTROL.intervals_till_gf_calculate_due and
-\ref RATE_CONTROL.frames_till_gf_update_due are also updated accordingly.
+The function first iterates through the first pass statistics in the GF group to
+accumulate various stats, using accumulate_this_frame_stats() and
+accumulate_next_frame_stats(). The accumulated statistics are then used to
+determine the use of the use of ALTREF frame along with other properties of the
+GF group. The values of \ref RATE_CONTROL.cur_gf_index, \ref
+RATE_CONTROL.intervals_till_gf_calculate_due and \ref
+RATE_CONTROL.frames_till_gf_update_due are also updated accordingly.
-The function \ref av1_gop_setup_structure() is called at the end to
-determine the frame layers and reference maps in the GF group, as shown in
-[TODO BohalLi@]. The (TODO REF) construct_multi_layer_gf_structure()
-function sets the frame update types for each frame and the group structure.
+The function \ref av1_gop_setup_structure() is called at the end to determine
+the frame layers and reference maps in the GF group, where the
+construct_multi_layer_gf_structure() function sets the frame update types for
+each frame and the group structure.
- If ALTREF frames are allowed for the GF group: the first frame is set to
- KF_UPDATE, OVERLAY_UPDATE or GF_UPDATE based on the previous GF group
- (if it exists). The last frame of the GF group is set to ARF_UPDATE.
- Then in (TODO REF) set_multi_layer_params(), frame update types are
- determined recursively in a binary tree fashion, and assigned to give
- the final IBBB structure for the group.
- - If the current branch has more than 2 frames and we have not reached
- maximum layer depth, then the middle frame is set as INTNL_ARF_UPDATE,
- and the left and right branches are processed recursively.
- - If the current branch has less than 3 frames, or we have reached maximum
- layer depth, then every frame in the branch is set to LF_UPDATE.
-- If ALTREF frame is not allowed for the GF group: the first frame is set to
- KF_UPDATE, OVERLAY_UPDATE or GF_UPDATE, and the rest of them are set as
- LF_UPDATE. This basically forms an IPPP GF group structure.
+ KF_UPDATE, GF_UPDATE or ARF_UPDATE. The last frames of the GF group is set to
+ OVERLAY_UPDATE. Then in set_multi_layer_params(), frame update
+ types are determined recursively in a binary tree fashion, and assigned to
+ give the final IBBB structure for the group. - If the current branch has more
+ than 2 frames and we have not reached maximum layer depth, then the middle
+ frame is set as INTNL_ARF_UPDATE, and the left and right branches are
+ processed recursively. - If the current branch has less than 3 frames, or we
+ have reached maximum layer depth, then every frame in the branch is set to
+ LF_UPDATE.
-The encoder may use Temporal dependancy modelling (TPL - see
-\ref architecture_enc_tpl) to determine whether we should use a maximum length
-of 32 or 16 for the current GF group. This requires calls to
-\ref define_gf_group() but should not change other settings (since it is in
-essence a trial). This special case is indicated by the setting parameter
-<b>is_final_pass</b> for to zero.
+- If ALTREF frame is not allowed for the GF group: the frames are set
+ as LF_UPDATE. This basically forms an IPPP GF group structure.
+
+As mentioned, the encoder may use Temporal dependancy modelling (TPL - see \ref
+architecture_enc_tpl) to determine whether we should use a maximum length of 32
+or 16 for the current GF group. This requires calls to \ref define_gf_group()
+but should not change other settings (since it is in essence a trial). This
+special case is indicated by the setting parameter <b>is_final_pass</b> for to
+zero.
For single pass encodes where look-ahead processing is disabled
(\ref AV1_COMP.lap_enabled = 0), \ref define_gf_group_pass0() is used
diff --git a/doc/dev_guide/tplgfgroupdiagram.png b/doc/dev_guide/tplgfgroupdiagram.png
new file mode 100644
index 0000000..582049a
--- /dev/null
+++ b/doc/dev_guide/tplgfgroupdiagram.png
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