How to access data from GMemoryOutputStream - c++

Question

I want to decode an audio file and store the PCM/int values into an array. For that I use gstreamer and the giostreamsink, which gives me a GMemoryOutputStream. So far so good, but how can I now access or loop through the GMemoryOutputStream?
What I did to get the gpointer:
gpointer out_data = g_memory_output_stream_get_data(G_MEMORY_OUTPUT_STREAM(stream));
but what can I do now with that gpointer? How can I access the stream data?
The full code that I have so far:
#include <string>
#include <stdio.h>
#include <gst/gst.h>
#include <gio/gio.h>
#include <boost/thread.hpp>
static void on_pad_added(GstElement *decodebin,
GstPad *pad,
gpointer data) {
GstElement *convert = (GstElement *) data;
GstCaps *caps;
GstStructure *str;
GstPad *audiopad;
audiopad = gst_element_get_static_pad(convert, "sink");
if (GST_PAD_IS_LINKED(audiopad)) {
g_object_unref(audiopad);
return;
}
caps = gst_pad_get_caps(pad);
str = gst_caps_get_structure(caps, 0);
printf("here %s\n",gst_structure_get_name(str));
if (!g_strrstr(gst_structure_get_name(str), "audio")) {
gst_caps_unref(caps);
gst_object_unref(audiopad);
return;
}
gst_caps_unref(caps);
gst_pad_link(pad, audiopad);
g_object_unref(audiopad);
}
static gboolean bus_call(GstBus *bus,
GstMessage *msg,
gpointer data) {
GMainLoop *loop = (GMainLoop*)data;
switch (GST_MESSAGE_TYPE(msg)) {
case GST_MESSAGE_EOS:
g_print ("End of stream\n");
g_main_loop_quit(loop);
break;
case GST_MESSAGE_ERROR: {
gchar *debug;
GError *error;
gst_message_parse_error(msg, &error, &debug);
g_free (debug);
g_printerr("Error: %s\n", error->message);
g_error_free(error);
g_main_loop_quit(loop);
break;
}
default:
break;
}
return true;
}
int main (int argc, char **argv) {
gst_init(&argc, &argv);
GstElement *pipeline, *source, *decode, *sink, *convert;
int rate = 44100;
int channels = 1;
int depth = 16;
bool output_signed = true;
GMainLoop *loop;
GstBus *bus;
guint bus_watch_id;
GMemoryOutputStream *stream;
gpointer out_data;
// loop
loop = g_main_loop_new(NULL, false);
// pipeline
pipeline = gst_pipeline_new("test_pipeline");
// sink
stream = G_MEMORY_OUTPUT_STREAM(g_memory_output_stream_new(NULL, 0, (GReallocFunc)g_realloc, (GDestroyNotify)g_free));
sink = gst_element_factory_make ("giostreamsink", "sink");
g_object_set(G_OBJECT(sink), "stream", stream, NULL);
// source
source = gst_element_factory_make("filesrc", "source");
g_object_set(G_OBJECT(source), "location", "/home/sam/Desktop/audio/audio.wav", NULL);
// convert
convert = gst_element_factory_make("audioconvert", "convert");
// decode
decode = gst_element_factory_make("decodebin", "decoder");
// link decode to convert
g_signal_connect(decode, "pad-added", G_CALLBACK(on_pad_added), convert);
// bus
bus = gst_pipeline_get_bus(GST_PIPELINE (pipeline));
bus_watch_id = gst_bus_add_watch(bus, bus_call, loop);
gst_object_unref(bus);
// add elements into pipeline
gst_bin_add_many(GST_BIN(pipeline), source, decode, convert, sink, NULL);
// link source to decode
gst_element_link(source, decode);
// caps
GstCaps *caps;
caps = gst_caps_new_simple("audio/x-raw-int",
"rate", G_TYPE_INT, rate,
"channels", G_TYPE_INT, channels,
"width", G_TYPE_INT, depth,
"depth", G_TYPE_INT, depth,
"signed", G_TYPE_BOOLEAN, output_signed,
NULL);
// link convert to sink
gst_element_link_filtered(convert, sink, caps);
gst_caps_unref(caps);
// start playing
gst_element_set_state(GST_ELEMENT(pipeline), GST_STATE_PLAYING);
// iterate
g_print("Running...\n");
g_main_loop_run(loop);
// out of the main loop, clean up nicely
g_print("Returned, stopping playback\n");
gst_element_set_state(pipeline, GST_STATE_NULL);
g_print("Deleting pipeline\n");
gst_object_unref(GST_OBJECT(pipeline));
g_source_remove (bus_watch_id);
g_main_loop_unref(loop);
// get data
g_print("get data\n");
out_data = g_memory_output_stream_get_data(G_MEMORY_OUTPUT_STREAM(stream));
unsigned long size = g_memory_output_stream_get_size(G_MEMORY_OUTPUT_STREAM(stream));
unsigned long sizeData = g_memory_output_stream_get_data_size(G_MEMORY_OUTPUT_STREAM(stream));
std::cout << "stream size: " << size << std::endl;
std::cout << "stream data size: " << sizeData << std::endl;
for (int i = 0; i < 5; ++i) {
// std::cout << out_data[i] << std::endl; // not working
}
return 0;
}

Answer 1

I solved the problem, I had to cast the gpointer to gint16*:
std::vector<int16_t> data;
for (unsigned long i = 0; i < sizeData/2; ++i) {
data.push_back(((gint16*)out_data)[i]);
}
The casting has to be changed, depending on the depth you use e.g. depth 8 and unsigned guint8* and change also the for loop limit.
The full code for those interested:
#include <string>
#include <stdio.h>
#include <gst/gst.h>
#include <gio/gio.h>
#include <boost/thread.hpp>
static void on_pad_added(GstElement *decodebin,
GstPad *pad,
gpointer data) {
GstElement *convert = (GstElement *) data;
GstCaps *caps;
GstStructure *str;
GstPad *audiopad;
audiopad = gst_element_get_static_pad(convert, "sink");
if (GST_PAD_IS_LINKED(audiopad)) {
g_object_unref(audiopad);
return;
}
caps = gst_pad_get_caps(pad);
str = gst_caps_get_structure(caps, 0);
printf("here %s\n",gst_structure_get_name(str));
if (!g_strrstr(gst_structure_get_name(str), "audio")) {
gst_caps_unref(caps);
gst_object_unref(audiopad);
return;
}
gst_caps_unref(caps);
gst_pad_link(pad, audiopad);
g_object_unref(audiopad);
}
static gboolean bus_call(GstBus *bus,
GstMessage *msg,
gpointer data) {
GMainLoop *loop = (GMainLoop*)data;
switch (GST_MESSAGE_TYPE(msg)) {
case GST_MESSAGE_EOS:
g_print ("End of stream\n");
g_main_loop_quit(loop);
break;
case GST_MESSAGE_ERROR: {
gchar *debug;
GError *error;
gst_message_parse_error(msg, &error, &debug);
g_free (debug);
g_printerr("Error: %s\n", error->message);
g_error_free(error);
g_main_loop_quit(loop);
break;
}
default:
break;
}
return true;
}
int main (int argc, char **argv) {
gst_init(&argc, &argv);
GstElement *pipeline, *source, *decode, *sink, *convert;
int rate = 44100;
int channels = 1;
int depth = 16;
bool output_signed = true;
GMainLoop *loop;
GstBus *bus;
guint bus_watch_id;
GMemoryOutputStream *stream;
gpointer out_data;
// loop
loop = g_main_loop_new(NULL, false);
// pipeline
pipeline = gst_pipeline_new("test_pipeline");
// sink
stream = G_MEMORY_OUTPUT_STREAM(g_memory_output_stream_new(NULL, 0, (GReallocFunc)g_realloc, (GDestroyNotify)g_free));
sink = gst_element_factory_make ("giostreamsink", "sink");
g_object_set(G_OBJECT(sink), "stream", stream, NULL);
// source
source = gst_element_factory_make("filesrc", "source");
g_object_set(G_OBJECT(source), "location", "/home/sam/Desktop/audio/audio.wav", NULL);
// convert
convert = gst_element_factory_make("audioconvert", "convert");
// decode
decode = gst_element_factory_make("decodebin", "decoder");
// link decode to convert
g_signal_connect(decode, "pad-added", G_CALLBACK(on_pad_added), convert);
// bus
bus = gst_pipeline_get_bus(GST_PIPELINE (pipeline));
bus_watch_id = gst_bus_add_watch(bus, bus_call, loop);
gst_object_unref(bus);
// add elements into pipeline
gst_bin_add_many(GST_BIN(pipeline), source, decode, convert, sink, NULL);
// link source to decode
gst_element_link(source, decode);
// caps
GstCaps *caps;
caps = gst_caps_new_simple("audio/x-raw-int",
"rate", G_TYPE_INT, rate,
"channels", G_TYPE_INT, channels,
"width", G_TYPE_INT, depth,
"depth", G_TYPE_INT, depth,
"signed", G_TYPE_BOOLEAN, output_signed,
NULL);
// link convert to sink
gst_element_link_filtered(convert, sink, caps);
gst_caps_unref(caps);
// start playing
gst_element_set_state(GST_ELEMENT(pipeline), GST_STATE_PLAYING);
// iterate
g_print("Running...\n");
g_main_loop_run(loop);
// out of the main loop, clean up nicely
g_print("Returned, stopping playback\n");
gst_element_set_state(pipeline, GST_STATE_NULL);
g_print("Deleting pipeline\n");
gst_object_unref(GST_OBJECT(pipeline));
g_source_remove (bus_watch_id);
g_main_loop_unref(loop);
// get data
g_print("get data\n");
out_data = g_memory_output_stream_get_data(G_MEMORY_OUTPUT_STREAM(stream));
unsigned long size = g_memory_output_stream_get_size(G_MEMORY_OUTPUT_STREAM(stream));
unsigned long sizeData = g_memory_output_stream_get_data_size(G_MEMORY_OUTPUT_STREAM(stream));
std::cout << "stream size: " << size << std::endl;
std::cout << "stream data size: " << sizeData << std::endl;
// access data and store in vector
std::vector<int16_t> data;
for (unsigned long i = 0; i < sizeData/2; ++i) {
data.push_back(((gint16*)out_data)[i]);
}
return 0;
}