Best way to save jpeg from Gstreamer appsinnk - c

Question

I have a USB camera generating MJPEG stream which I am reading by my app. I would like to save the images (a JPEG). I have tried to do so by creating a second pipeline from the app to the image, but I am the first one to admit that I have no idea how to correctly terminate such a pipeline. The implementation crashes the app after average of 3 images taken.
I do not wish to encode a re-decode the image if possible. Is there a different way to save the image than creating the second pipeline/decoding the image?
My current implemenation is:
static GstFlowReturn new_sample_jpeg(GstElement * elt, MyStruct *data){
GstSample *sample;
GstBuffer *buffer;
GstMemory *memory;
GstMapInfo info;
GstFlowReturn ret = GST_FLOW_OK;
// get the sample from appsink
sample = gst_app_sink_pull_sample (GST_APP_SINK (elt));
//if recording, send the sample to recording sink
if (data->saveVideo) addSampleFromAppsinkVideo(gst_sample_copy(sample));
buffer = gst_sample_get_buffer (sample);
if (buffer != NULL){
memory = gst_buffer_get_memory (buffer, 0);
if (memory != NULL) {
//now all data are image data. If image wanted->image save!
if (data->saveImage) saveSampleFromAppsinkJpeg(gst_sample_copy(sample));
...
gst_memory_unref(memory);
} else {
std::cerr << "sample_from_sink(): ERROR memory" << std::endl;
}
} else {
std::cerr << "sample_from_sink(): ERROR buffer " << gst_buffer_get_size(buffer) << std::endl;
}
gst_sample_unref (sample);
return ret;
}
int saveSampleFromAppsinkJpeg( GstSample *sample){
//create the pipeline
GstStateChangeReturn ret;
GstElemenent *source = gst_element_factory_make ("appsrc", "appsrc_capture");
GstElemenent *sink = gst_element_factory_make ("multifilesink", "sink_capture");
g_object_set (sink, "location", "some/path.jpg", NULL);
GstElemenent *pipeline = gst_pipeline_new ("pipeline_img");
if (!pipeline || !source || !sink) {
g_printerr ("Not all elements could be created.\n");
return false;
}
GstCaps *caps;
caps = gst_sample_get_caps(sample);
gst_app_src_set_caps(GST_APP_SRC(source), caps);
gst_app_src_set_duration(GST_APP_SRC(source), GST_TIME_AS_MSECONDS(80));
gst_app_src_set_stream_type(GST_APP_SRC(source), GST_APP_STREAM_TYPE_STREAM);
gst_app_src_set_latency(GST_APP_SRC(source), -1, 0);
gst_bin_add_many (GST_BIN (pipeline), source, sink, NULL);
gst_caps_unref (caps);
if (gst_element_link_many(source, sink, NULL) != TRUE) {
g_printerr ("Elements could not be linked.\n");
gst_object_unref (pipeline);
return -1;
}
ret = gst_element_set_state (pipeline, GST_STATE_PLAYING);
if (ret == GST_STATE_CHANGE_FAILURE) {
g_printerr ("Unable to set the pipeline to the playing state.\n");
gst_object_unref (pipeline);
return -1;
}
//push the image in the pipeline
GstFlowReturn status = GstFlowReturn::GST_FLOW_OK;
status = gst_app_src_push_sample(GST_APP_SRC(source),sample);
if (status != GstFlowReturn::GST_FLOW_OK) g_printerr ("Sample for saving image not pushed: code %d.\n", status);
usleep(500000); // not clean. But how to do this better?
status = gst_app_src_end_of_stream(GST_APP_SRC(source));
if (status != GstFlowReturn::GST_FLOW_OK) g_printerr ("EOS for saving image not pushed %d \n", status);
usleep(500000); // not clean. But how to do this better?
//end the pipeline
GstMessage *EndMessage = gst_message_new_eos(&pipeline->object);
gst_bus_post(pipeline->bus, EndMessage);
gst_element_send_event(pipeline, gst_event_new_eos());
/* Free resources */
if (EndMessage != NULL) gst_message_unref (EndMessage);
status = gst_app_src_end_of_stream(GST_APP_SRC(source));
//end the pipeline
usleep(500000); // not clean. But how to do this better?
gst_element_set_state (pipeline, GST_STATE_NULL);
GstState currentState = GST_STATE_READY;
GstClockTime timeout = 50;
uint8_t safetyCounter = 255;
do{
gst_element_get_state(pipeline, &currentState, NULL,timeout );
if (safetyCounter-- == 0){ //ok, something is seqiously broken here
break;
}
usleep(10000);
} while (currentState != GST_STATE_NULL);
gst_object_unref (pipeline);
gst_sample_unref(sample);
return 1;
}

Answer 1

So in the end I am just using the uvc library (https://github.com/libuvc/libuvc) to decode the mjpeg into rgb, and then I encode it as jpeg with jpeglib. Pretty wastefull, but working.