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[FFmpeg-devel,v2] libavcodec/libx264: fix reference frame computation based on level

Message ID ecWnJA0TquhqD5UyF3JZqthZk6AAKBLvqFl48XeqKEq3dqqw_ZdnOe5leNmjkecTCUlXMR5AjFEDuwdgDbieP5-vNP60NncosmV8LDjEhRQ=@protonmail.com
State Superseded
Headers show
Series [FFmpeg-devel,v2] libavcodec/libx264: fix reference frame computation based on level | expand

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Commit Message

Josh Brewster April 17, 2020, 10:41 a.m. UTC 
> Hi,
>
> > From: ffmpeg-devel ffmpeg-devel-bounces@ffmpeg.org On Behalf Of
> > josh.brewster@protonmail.com
> > Sent: Friday, April 17, 2020 07:05
> > To: ffmpeg-devel@ffmpeg.org
> > Subject: [FFmpeg-devel] [PATCH] libavcodec/libx264: fix reference frame
> > computation based on level
> > Hell, can someone please review this patch? It fixes a wrong reference frame
> > computation problem when using parameters such as "-level 31" instead of
> > "-level 3.1".
> > diff --git a/libavcodec/libx264.c b/libavcodec/libx264.c
> > index a08fe0ce76..1149f2d668 100644
> > --- a/libavcodec/libx264.c
> > +++ b/libavcodec/libx264.c
> > @@ -701,11 +701,14 @@ FF_ENABLE_DEPRECATION_WARNINGS
> >
> >          if (!strcmp(x4->level, "1b")) {
> >              level_id = 9;
> >
> >
> > -          } else if (strlen(x4->level) <= 3){
> >
> >
> >
> > -          } else if (av_strtod(x4->level, NULL) < 7){
> >                level_id = av_strtod(x4->level, &tail) * 10 + 0.5;
> >                if (*tail)
> >                    level_id = -1;
> >            }
> >
> >
> > -          else {
> >
> >
>
> Wrong coding style for "else", should be "} else {"
>
> > -              level_id = av_strtod(x4->level, NULL);
> >
> >
> > -          }
> >            if (level_id <= 0)
> >                av_log(avctx, AV_LOG_WARNING, "Failed to parse level\\n");
> >
> >
>
> This part of code of parsing level_id seems redundant, since PARSE_X264_OPT("level", level) has
> been called and did the same thing inside libx264, which converts x4->level to x4->params.i_level_idc
> correctly (equals 31), regardless of "-level 3.1 or level 31".
>
> Hence it would be better to use x4->params.i_level_idc directly.
>
> -   Linjie
>
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> ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".

Hi Linjie, thanks for the feedback. I have changed the patch to use the right parameter. I only made sure that the level was positive because its initial value was -1.
> else if (x4->params.i_level_idc >= 0) {
Let me know if I need to reject 0 too. It seemed like premature optimization as the level simply wouldn't be present in x264_levels.

Comments

Fu, Linjie April 18, 2020, 2:55 a.m. UTC | #1 
> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of
> Josh Brewster
> Hi Linjie, thanks for the feedback. I have changed the patch to use the right
> parameter. I only made sure that the level was positive because its initial
> value was -1.
> > else if (x4->params.i_level_idc >= 0) {
> Let me know if I need to reject 0 too. It seemed like premature optimization
> as the level simply wouldn't be present in x264_levels.
I'd say yes, level_idc = 0 is possible but invalid by PARSE_X264_OPT(), which  seems
make no sense to calculate refs from x264_levels[] table.

- Linjie
diff mbox series

Patch

From 98344809c22d574959eb4351a1cc03f431b4617c Mon Sep 17 00:00:00 2001
From: Josh Brewster <josh.brewster@protonmail.com>
Date: Thu, 16 Apr 2020 22:50:29 +0200
Subject: [PATCH] libavcodec/libx264: fix reference frame computation based on
 level

The current implementation allows passing levels to libavcodec as
integers (such as "31" instead of "3.1").

However, in this case, the maximum reference frame value per level was
ignored because libavcodec converted the string to 310 instead of 31.

Since libx264 has correctly parsed the level to int
(x4->params.i_level_idc), we should rely on this value instead of
attempting to parse the level string on our own.

Signed-off-by: Josh Brewster <josh.brewster@protonmail.com>
---
 libavcodec/libx264.c | 16 ++--------------
 1 file changed, 2 insertions(+), 14 deletions(-)

diff --git a/libavcodec/libx264.c b/libavcodec/libx264.c
index a08fe0ce76..a4caa5b5db 100644
--- a/libavcodec/libx264.c
+++ b/libavcodec/libx264.c
@@ -692,25 +692,13 @@  FF_ENABLE_DEPRECATION_WARNINGS
         x4->params.rc.f_qcompress       = avctx->qcompress; /* 0.0 => cbr, 1.0 => constant qp */
     if (avctx->refs >= 0)
         x4->params.i_frame_reference    = avctx->refs;
-    else if (x4->level) {
+    else if (x4->params.i_level_idc >= 0) {
         int i;
         int mbn = AV_CEIL_RSHIFT(avctx->width, 4) * AV_CEIL_RSHIFT(avctx->height, 4);
-        int level_id = -1;
-        char *tail;
         int scale = X264_BUILD < 129 ? 384 : 1;
 
-        if (!strcmp(x4->level, "1b")) {
-            level_id = 9;
-        } else if (strlen(x4->level) <= 3){
-            level_id = av_strtod(x4->level, &tail) * 10 + 0.5;
-            if (*tail)
-                level_id = -1;
-        }
-        if (level_id <= 0)
-            av_log(avctx, AV_LOG_WARNING, "Failed to parse level\n");
-
         for (i = 0; i<x264_levels[i].level_idc; i++)
-            if (x264_levels[i].level_idc == level_id)
+            if (x264_levels[i].level_idc == x4->params.i_level_idc)
                 x4->params.i_frame_reference = av_clip(x264_levels[i].dpb / mbn / scale, 1, x4->params.i_frame_reference);
     }
 
-- 
2.26.0