hw_base_enc: inject side data to crop output for AV1

Unlike H264/H265, AV1 contains no fields to crop encoded output
to specific sizes.
AMD's hardware cannot handle encoding of unaligned dimensions for
AV1, hence it codes 1920x1080 as 1920x1088.

Add side data to crop the output back to the original dimensions.
There's an AV1-spec extension planned to fix this here:
AOMediaCodec/av1-spec#346

But it seems to have stuck for now.

libavcodec/hw_base_encode.c

@@ -22,6 +22,7 @@
 #include "libavutil/log.h"
 #include "libavutil/mem.h"
 #include "libavutil/pixdesc.h"
+#include "libavutil/intreadwrite.h"
 
 #include "encode.h"
 #include "avcodec.h"
@@ -551,6 +552,30 @@ int ff_hw_base_encode_set_output_property(FFHWBaseEncodeContext *ctx,
                                 (3 * ctx->output_delay + ctx->async_depth)];
     }
 
+    if ((avctx->codec_id == AV_CODEC_ID_AV1) &&
+        ((avctx->coded_width != avctx->width) ||
+         (avctx->coded_height != avctx->height)) {
+        int err;
+        size_t crop_data_size = 4*4;
+
+        uint8_t *crop_data = av_mallocz(crop_data_size);
+        if (!crop_data) {
+            av_buffer_unref(&pkt->buf);
+            return AVERROR(ENOMEM);
+        }
+
+        AV_WL32(&crop_data[2], ctx->surface_width - avctx->width);
+        AV_WL32(&crop_data[3], ctx->surface_height - avctx->height);
+
+        err = av_packet_add_side_data(pkt, AV_PKT_DATA_FRAME_CROPPING,
+                                      crop_data, crop_data_size);
+        if (err < 0) {
+            av_buffer_unref(&pkt->buf);
+            av_free(crop_data);
+            return err;
+        }
+    }
+
     return 0;
 }