libavcodec/qsvenc: Add dynamic setting support of low_delay_brc to av1_qsv

Signed-off-by: Wenbin Chen <wenbin.chen@intel.com>

doc/encoders.texi

@@ -3344,7 +3344,7 @@ Supported in h264_qsv.
 Change these value to reset qsv codec's max/min qp configuration.
 
 @item @var{low_delay_brc}
-Supported in h264_qsv and hevc_qsv.
+Supported in h264_qsv, hevc_qsv and av1_qsv.
 Change this value to reset qsv codec's low_delay_brc configuration.
 
 @item @var{framerate}

libavcodec/qsvenc.c

@@ -1127,6 +1127,7 @@ static int init_video_param(AVCodecContext *avctx, QSVEncContext *q)
         } else if (avctx->codec_id == AV_CODEC_ID_AV1) {
             if (q->low_delay_brc >= 0)
                 q->extco3.LowDelayBRC = q->low_delay_brc ? MFX_CODINGOPTION_ON : MFX_CODINGOPTION_OFF;
+            q->old_low_delay_brc = q->low_delay_brc;
         }
 
         if (avctx->codec_id == AV_CODEC_ID_HEVC) {
@@ -2213,7 +2214,9 @@ static int update_low_delay_brc(AVCodecContext *avctx, QSVEncContext *q)
 {
     int updated = 0;
 
-    if (avctx->codec_id != AV_CODEC_ID_H264 && avctx->codec_id != AV_CODEC_ID_HEVC)
+    if (avctx->codec_id != AV_CODEC_ID_H264 &&
+        avctx->codec_id != AV_CODEC_ID_HEVC &&
+        avctx->codec_id != AV_CODEC_ID_AV1)
         return 0;
 
     UPDATE_PARAM(q->old_low_delay_brc, q->low_delay_brc);