[gst-devel] gstreamer gstbasetransform

Federico Paganini black_eagle85 at hotmail.com
Mon Feb 1 11:51:59 CET 2010

Hi Micheal,

i am following your advice in order to allocate the output buffer. But
i have a problem, I insert my encryption plug-in in a pipeline and when
i try to run the pipeline i obtain a file with only audio track; video
track is disappeared. My pipeline is this:


                                      -->queue--->decoder--->audioconverter-->encoder--->identity--->queue--- AUDIO

---> mux-->filesink

I have annex in this mail my gst_destool_chain() function in which i
have inserted the buffer output allocation and the encryption plug-in: 

Can you say to me if is correct? Thanks in advance!!!!!

/* chain function

 * this function does the actual processing


static GstFlowReturn

gst_destool_chain (GstPad * pad, GstBuffer * inbuf)


  GstDesTool *filter;

  GstBuffer *outbuf;



  if (filter->silent == FALSE)


    //printf ("I'm plugged, therefore I'm in.\n");

    //filter->process (filter, GST_BUFFER_DATA (buf), GST_BUFFER_SIZE (buf));

    //Calculating the dimensione of the output buffer 

        guint padSize = (8 - inbuf->size % 8);

        guint newSize = inbuf->size + padSize;

        guint pad;


    //Allocate output buffer

    outbuf= gst_buffer_new_and_alloc (newSize);



    gst_buffer_set_caps (outbuf, GST_PAD_CAPS (filter->srcpad));


    guint8 startCode[3] = { 0x00, 0x00, 0x01 };

    if ( (guint8*)memmem( inbuf->data, inbuf->size, startCode, 3 ) == inbuf->data )      


            memcpy( outbuf->data, inbuf->data, inbuf->size );


    // Doing padding   

        for(  pad = 0; pad < padSize; ++pad )


            outbuf->data[ inbuf->size + pad ] = padSize;


        // prepare des key 

        DES_key_schedule schedule;

        DES_set_key ( (des_cblock*)filter->key, &schedule );

        //do encryption

        DES_ncbc_encrypt( inbuf->data + 4, outbuf->data + 4,
newSize - 4, &schedule, (des_cblock*)filter->iv, DES_ENCRYPT );




        fprintf( stderr, "begin of frame is not expected start code, dropping\n");





  /* just push out the incoming buffer without touching it */

  gst_buffer_unref (inbuf);

  return gst_pad_push (filter->srcpad, outbuf);


> Date: Sat, 30 Jan 2010 15:54:28 -0800
> From: msmith at xiph.org
> To: gstreamer-devel at lists.sourceforge.net
> Subject: Re: [gst-devel] gstreamer gstbasetransform
> On Sat, Jan 30, 2010 at 2:43 AM, Federico Paganini
> <black_eagle85 at hotmail.com> wrote:
> > Hi,
> >
> > I briefly explain to you my problem. For my thesis i am developing a
> > gstreamer plug-in that encrypt an mpeg4 video with DES in CBC mode. The
> > encryption is made frame by frame and because a frame doesn't contain an
> > exact number of DES BLOCK SIZE(64 bit) i must padding the final bytes of the
> > frame. Because i use padding the dimension of the frame in output is greater
> > than that in input. For this reason i must allocate an output buffer of a
> > precise size. So in the trasform function of my plug in i have tried to call
> > this function: gst_base_transform_prepare_output_buffer( base, inbuf,
> > newSize, inbuf->caps,&outbuf ); but when i try to compile i have this
> > error:error: implicit declaration of function
> > ‘gst_base_transform_prepare_output_buffer’ nevertheless i have done the
> > include of gstbasetransform.h.
> > I would be very happy if you can say to me how i must to  allocate an output
> > buffer that is larger than input.
> For what you're doing, you probably don't want to make your element a
> subclass of GstBaseTransform at all - instead you should directly
> subclass GstElement. You can use gst_pad_alloc_buffer() or
> gst_buffer_new_and_alloc() to allocate your output buffer with any
> size you want.
> Mike
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