[SailfishDevel] LED Flash functionality on a real Jolla

christopher.lamb at thurweb.ch christopher.lamb at thurweb.ch
Thu Jan 23 21:10:19 UTC 2014

Hi Mohammed

I have been trying to implement your suggestion, but am still having  
problems ...

The Nokia code quoted in my original post did not have an explicit  
sink (and on the N9 worked without one). But following the tutorial in  
the link below I have added one to the my code.


The code compiles and runs, but the LED does not respond. On startup I  
get errors like:

(GSTTorch:14916): GLib-GObject-CRITICAL **: Object class  
GstDroidCamSrc doesn't implement property 'scene-mode' from interface  

(GSTTorch:14916): GLib-GObject-CRITICAL **: Object class  
GstDroidCamSrc doesn't implement property 'noise-reduction' from  
interface 'GstPhotography'
...more of the same ...


I confess that I have not yet fully understood the Gstreamer  
architecture, so my code is very much "best guess" attempt.

thanks for your help,


//start gsttorch.h
#ifndef GSTTORCH_H
#define GSTTORCH_H

#include <QObject>
#include <gst/gstelement.h>

class GstTorch : public QObject

     Q_PROPERTY(bool status READ status WRITE setStatus NOTIFY statusChanged)
     explicit GstTorch(QObject *parent = 0);

     void start();
     void stop();
     Q_INVOKABLE void toggle();

     bool status();
     void setStatus(bool on);

     void statusChanged(bool on);

     GstElement *pipeline;
     GstElement *src;
     GstElement *sink;
     bool mStatus; // true = on

#endif // GSTTORCH_H
//end gsttorch.h

//start gsttorch.cpp
//thanks to:

#include "gsttorch.h"
#include <gst/gst.h>
#include <QDebug>

GstTorch::GstTorch(QObject *parent) :
     QObject(parent), pipeline(0), src(0), sink(0), mStatus(false)
     //gst-launch-0.10 droidcamsrc video-torch=1 viewfinder-mode=1 ! fakesink
     gst_init(NULL, NULL);
     src = gst_element_factory_make("droidcamsrc", "src");
     sink = gst_element_factory_make("droideglsink", "sink");
     pipeline = gst_pipeline_new ("test-pipeline");
     if (!src || !sink || !pipeline) {
     /* Build the pipeline */
     gst_bin_add_many (GST_BIN (pipeline), src, sink, NULL);
     if (gst_element_link (src, sink) != TRUE) {
         qDebug() << "Elements could not be linked!";
         gst_object_unref (pipeline);
     g_object_set(G_OBJECT(src), "video-torch", 1, NULL);
     g_object_set(G_OBJECT(src), "mode", 1, NULL);
     gst_element_set_state(pipeline, GST_STATE_NULL);

void GstTorch::start(){
     qDebug() << "START";
     gst_element_set_state(pipeline, GST_STATE_PLAYING);

void GstTorch::stop(){
     qDebug() << "STOP";
     gst_element_set_state(pipeline, GST_STATE_NULL);

void GstTorch::toggle(){
     qDebug() << "TOGGLE";

bool  GstTorch::status(){
     qDebug() << "STATUS";
     return mStatus;

void  GstTorch::setStatus(bool on){
     qDebug() << "SET STATUS" << on;
     if (on){
         emit statusChanged(true);
     } else {
         emit statusChanged(false);
     mStatus = on;
//end gsttorch.cpp

Zitat von "Mohammed Hassan" <mohammed.hassan at jollamobile.com>:

> On Wed, Jan 22, 2014 at 08:29:19PM +0100, christopher.lamb at thurweb.ch wrote:
> [...]
>> Solution 3)
>> Via a Gstreamer QML Plugin.
>> I dug out some old code that worked on Harmattan, basically the code
>> from this link to create a qml plugin
>> http://developer.nokia.com/Community/Wiki/How_to_turn_your_camera_flash_into_a_torch_on_Harmattan_using_GStreamer
>> On Sailfish this compiles, but gives the following error when I
>> start the torch.
>> (GSTTorch:708): GStreamer-CRITICAL **: gst_element_set_state:
>> assertion `GST_IS_ELEMENT (element)' failed
> This is not the recommended way but it's the only way to get flash  
> light to work but I have to
> warn you that it wil prevent your app from entering harbour. You  
> will also have to make use
> of resource policy engine to arbitrate access to camera. Failing to  
> do so will lead to breaking
> jolla camera app.
> Simply replace subdevsrc with droidcamsrc and use droideglsink as  
> the sink and
> it should work fine.
> Cheers,
> _______________________________________________
> SailfishOS.org Devel mailing list

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