nvenc: implement flush to help allow an encoder to be re-used

It can be useful to re-use an encoder instance when doing segmented
encodings, and this requires flushing the encoder at the start of
each segment.

libavcodec/nvenc.c

@@ -2262,3 +2262,8 @@ int ff_nvenc_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
 
     return 0;
 }
+
+av_cold void ff_nvenc_encode_flush(AVCodecContext *avctx)
+{
+    ff_nvenc_send_frame(avctx, NULL);
+}

libavcodec/nvenc.h

@@ -214,6 +214,8 @@ int ff_nvenc_receive_packet(AVCodecContext *avctx, AVPacket *pkt);
 int ff_nvenc_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
                           const AVFrame *frame, int *got_packet);
 
+void ff_nvenc_encode_flush(AVCodecContext *avctx);
+
 extern const enum AVPixelFormat ff_nvenc_pix_fmts[];
 
 #endif /* AVCODEC_NVENC_H */

libavcodec/nvenc_h264.c

@@ -240,6 +240,7 @@ AVCodec ff_h264_nvenc_encoder = {
     .receive_packet = ff_nvenc_receive_packet,
     .encode2        = ff_nvenc_encode_frame,
     .close          = ff_nvenc_encode_close,
+    .flush          = ff_nvenc_encode_flush,
     .priv_data_size = sizeof(NvencContext),
     .priv_class     = &h264_nvenc_class,
     .defaults       = defaults,

libavcodec/nvenc_hevc.c

@@ -198,6 +198,7 @@ AVCodec ff_hevc_nvenc_encoder = {
     .receive_packet = ff_nvenc_receive_packet,
     .encode2        = ff_nvenc_encode_frame,
     .close          = ff_nvenc_encode_close,
+    .flush          = ff_nvenc_encode_flush,
     .priv_data_size = sizeof(NvencContext),
     .priv_class     = &hevc_nvenc_class,
     .defaults       = defaults,

libavcodec/version.h

@@ -29,7 +29,7 @@
 
 #define LIBAVCODEC_VERSION_MAJOR  58
 #define LIBAVCODEC_VERSION_MINOR  65
-#define LIBAVCODEC_VERSION_MICRO 102
+#define LIBAVCODEC_VERSION_MICRO 103
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
                                                LIBAVCODEC_VERSION_MINOR, \