libvpxenc: Support forcing keyframes

Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/libvpxenc.c

@@ -495,6 +495,7 @@ static int vp8_encode(AVCodecContext *avctx, AVPacket *pkt,
     struct vpx_image *rawimg = NULL;
     int64_t timestamp = 0;
     int res, coded_size;
+    vpx_enc_frame_flags_t flags = 0;
 
     if (frame) {
         rawimg                      = &ctx->rawimg;
@@ -505,10 +506,12 @@ static int vp8_encode(AVCodecContext *avctx, AVPacket *pkt,
         rawimg->stride[VPX_PLANE_U] = frame->linesize[1];
         rawimg->stride[VPX_PLANE_V] = frame->linesize[2];
         timestamp                   = frame->pts;
+        if (frame->pict_type == AV_PICTURE_TYPE_I)
+            flags |= VPX_EFLAG_FORCE_KF;
     }
 
     res = vpx_codec_encode(&ctx->encoder, rawimg, timestamp,
-                           avctx->ticks_per_frame, 0, ctx->deadline);
+                           avctx->ticks_per_frame, flags, ctx->deadline);
     if (res != VPX_CODEC_OK) {
         log_encoder_error(avctx, "Error encoding frame");
         return AVERROR_INVALIDDATA;