Connecting to a tee that's playing - linux

Question

I'm using gstreamer to stream video from a camera to an HLS sink and to also record that video to the filesystem as an MP4. I use a tee to split the video into the two paths. I wrote some code and got it working if I connect it all up and switch state to "play". But when I start the streaming and try to connect the splitmuxsink dynamically to the tee, the video files I record aren't valid (at least VLC won't play them). (The web stream continues to work just fine)
I've reduced my code to a simple version (below) where I start with one splimuxsink, sleep a while and then add a second one. Although the first splitmuxsink works great, the new one never generates usable video. To make the transitions, I switch the playing pipeline to pause, add the new elements (all in the paused state) and switch everything to play.
Following the gstream manual, I've tried more complicated switching procedures; adding a probe to block the new branch of the tee, etc. but the results are the same.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <ctype.h>
#include <gst/gst.h>
#include <assert.h>
using namespace std;
int main()
{
// Create a pipeline to write a file
printf("starting\n");
gst_init(NULL, NULL);
// Create the pipeline to host the elements
GstElement* pipeline = gst_pipeline_new("pipeline");
assert(pipeline != nullptr);
GstElement* camera = gst_element_factory_make("v4l2src", "v4l2src");
assert(camera != nullptr);
g_object_set(G_OBJECT(camera),
"device", "/dev/video2",
NULL);
GstElement* caps = gst_element_factory_make("capsfilter", "capsfilter");
assert(caps != nullptr);
g_object_set(G_OBJECT(caps),
"caps", gst_caps_from_string("video/x-h264,width=640,height=480,framerate=30/1"),
NULL);
GstElement* tee = gst_element_factory_make("tee", "tee");
GstElement* queue1 = gst_element_factory_make("queue", "queue1");
GstElement* h264parse1 = gst_element_factory_make("h264parse", "h264parse1");
GstElement* splitmux1 = gst_element_factory_make("splitmuxsink", "splitmux1");
g_object_set(G_OBJECT(splitmux1),
"location", "file%03d.mp4",
"max-size-time", 10000000000,
NULL);
assert(tee != nullptr && queue1 != nullptr && h264parse1 != nullptr && splitmux1 != nullptr);
// Attach them all to the pipeline
gst_bin_add_many(GST_BIN (pipeline), camera, caps, tee, queue1, h264parse1, splitmux1, NULL);
// Link the pieces
assert(true == gst_element_link_many(camera, caps, tee, NULL));
GstPad* srcpad = gst_element_get_request_pad(tee, "src_%u");
assert(srcpad != nullptr);
GstPad* dstpad = gst_element_get_static_pad (queue1, "sink");
assert(dstpad != nullptr);
assert(GST_PAD_LINK_OK == gst_pad_link(srcpad, dstpad));
assert(true == gst_element_link_many (queue1, h264parse1, splitmux1, NULL));
assert(GST_STATE_CHANGE_ASYNC == gst_element_set_state (pipeline, GST_STATE_PLAYING));
sleep(35);
printf("Attach the splitmuxsink\n");
// Now attach another sink
GstElement* queue2 = gst_element_factory_make("queue", "queue2");
assert(nullptr != queue2);
GstElement* h264parse2 = gst_element_factory_make("h264parse", "h264parse2");
assert(nullptr != h264parse2);
GstElement* splitmux2 = gst_element_factory_make("splitmuxsink", "splitmux2");
assert(nullptr != splitmux2);
g_object_set(G_OBJECT(splitmux2),
"location", "alt%03d.mp4",
"max-size-time", 10000000000,
NULL);
// Set all the states to paused before attaching
assert(GST_STATE_CHANGE_ASYNC == gst_element_set_state (splitmux2, GST_STATE_PAUSED));
assert(GST_STATE_CHANGE_SUCCESS == gst_element_set_state (h264parse2, GST_STATE_PAUSED));
assert(GST_STATE_CHANGE_SUCCESS == gst_element_set_state (queue2, GST_STATE_PAUSED));
assert(GST_STATE_CHANGE_NO_PREROLL == gst_element_set_state (pipeline, GST_STATE_PAUSED));
gst_bin_add_many (GST_BIN (pipeline), queue2, h264parse2, splitmux2, NULL);
assert(true == gst_element_link_many (queue2, h264parse2, splitmux2, NULL));
GstPad* srcpad2 = gst_element_get_request_pad(tee, "src_%u");
assert(nullptr != srcpad2);
GstPad* dstpad2 = gst_element_get_static_pad (queue2, "sink");
assert(nullptr != dstpad2);
assert(GST_PAD_LINK_OK == gst_pad_link(srcpad2, dstpad2));
assert(GST_STATE_CHANGE_ASYNC == gst_element_set_state (pipeline, GST_STATE_PLAYING));
sleep(65);
printf("all done\n");
}