[Libav-user] Querying v4l2 devices

[Lukasz Marek]

On 16.09.2016 23:39, Timur Guseynov wrote:
> Hi. I wrote the code for getting a list of input devices:
>
> avdevice_register_all();
>
>
> AVFormatContext*formatContext=avformat_alloc_context();
>
> AVInputFormat*inputFormat=NULL;
>
> while((inputFormat=av_input_video_device_next(inputFormat)))
>
> {
>
> formatContext->iformat=inputFormat;
>
>
> AVDeviceInfoList*deviceList=NULL;
>
> avdevice_list_devices(formatContext,&deviceList);
>
>
> if(deviceList)
>
> {
>
> for(inti=0;i<deviceList->nb_devices;++i)
>
> {
>
> AVDeviceInfo*device=deviceList->devices[i];
>
> ..........
>
> }
>
> }
>
>
> avdevice_free_list_devices(&deviceList);
>
>      }
>
>
> It fails with SIGSEGV on avdevice_list_devices when it comes to v4l2 input format.
> Why does it fail?
> How can I get list of video devices?
>
> Btw I'm using Ubuntu 16.04

I guess input device private data is not initialized, try to add this 
code right after formatContext->iformat=inputFormat, just replace s with 
formatContext

     if (s->iformat->priv_data_size > 0) {
         s->priv_data = av_mallocz(s->iformat->priv_data_size);
         if (s->iformat->priv_class) {
             *(const AVClass**)s->priv_data= s->iformat->priv_class;
             av_opt_set_defaults(s->priv_data);
         }
     } else
         s->priv_data = NULL;


Maybe ff_alloc_input_device_context function should be moved to 
libavdevice's public API