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>
Signed-off-by: Josh de Kock <josh@itanimul.li>

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);
     }