avcodec: vaapi_decode, do not set initial_pool_size if driver support…

…s frame pool resizing

Two benifites of this commit:
1. Save memory. If we play an 8k hevc, previous code we allocate 50M * 20(1 + 16 + 3) = 1G memory.16 is a waste for most playback cases.
2. Allow downstream cache more frames. A downstream lookahead encoder will cache some frames. 20 may not enough for it.

This commit will fix the following command
ffmpeg -hwaccel vaapi -hwaccel_output_format vaapi -i 100frames.264  -vf reverse -an -f null -

libavcodec/vaapi_decode.c

@@ -572,22 +572,24 @@ static int vaapi_decode_make_config(AVCodecContext *avctx,
         if (err < 0)
             goto fail;
 
-        frames->initial_pool_size = 1;
-        // Add per-codec number of surfaces used for storing reference frames.
-        switch (avctx->codec_id) {
-        case AV_CODEC_ID_H264:
-        case AV_CODEC_ID_HEVC:
-            frames->initial_pool_size += 16;
-            break;
-        case AV_CODEC_ID_VP9:
-        case AV_CODEC_ID_AV1:
-            frames->initial_pool_size += 8;
-            break;
-        case AV_CODEC_ID_VP8:
-            frames->initial_pool_size += 3;
-            break;
-        default:
-            frames->initial_pool_size += 2;
+        if (hwctx->driver_quirks & AV_VAAPI_DRIVER_QUIRK_FRAME_POOL_RESIZING) {
+            frames->initial_pool_size = 1;
+            // Add per-codec number of surfaces used for storing reference frames.
+            switch (avctx->codec_id) {
+            case AV_CODEC_ID_H264:
+            case AV_CODEC_ID_HEVC:
+                frames->initial_pool_size += 16;
+                break;
+            case AV_CODEC_ID_VP9:
+            case AV_CODEC_ID_AV1:
+                frames->initial_pool_size += 8;
+                break;
+            case AV_CODEC_ID_VP8:
+                frames->initial_pool_size += 3;
+                break;
+            default:
+                frames->initial_pool_size += 2;
+            }
         }
     }