obs-ffmpeg: Set framerate for AVCodecContext outputs

In avcodec.h, the docs for AVCodecContext->framerate say:
encoding: May be used to signal the framerate of CFR content to an
          encoder.

OBS is designed to always output Constant Frame Rate (CFR) content.
Instead of letting this be implied, let's explicitly set the framerate
per the docs.

plugins/obs-ffmpeg/obs-ffmpeg-output.c

@@ -256,6 +256,7 @@ static bool create_video_stream(struct ffmpeg_data *data)
 	context->width = data->config.scale_width;
 	context->height = data->config.scale_height;
 	context->time_base = (AVRational){ovi.fps_den, ovi.fps_num};
+	context->framerate = (AVRational){ovi.fps_num, ovi.fps_den};
 	context->gop_size = data->config.gop_size;
 	context->pix_fmt = closest_format;
 	context->color_range = data->config.color_range;

plugins/obs-ffmpeg/obs-ffmpeg-video-encoders.c

@@ -75,6 +75,7 @@ void ffmpeg_video_encoder_update(struct ffmpeg_video_encoder *enc, int bitrate,
 	enc->context->width = obs_encoder_get_width(enc->encoder);
 	enc->context->height = obs_encoder_get_height(enc->encoder);
 	enc->context->time_base = (AVRational){voi->fps_den, voi->fps_num};
+	enc->context->framerate = (AVRational){voi->fps_num, voi->fps_den};
 	enc->context->pix_fmt = pix_fmt;
 	enc->context->color_range = info->range == VIDEO_RANGE_FULL
 					    ? AVCOL_RANGE_JPEG