[vlc-devel] Green areas in the video when using vlc streaming

[Herman Schultz]

On 7/30/07, Jean-Paul Saman <jean-paul.saman at planet.nl> wrote:
>
> Herman Schultz wrote:
> > On 7/20/07, Jean-Paul Saman <jean-paul.saman at planet.nl> wrote:
> >> Herman Schultz wrote:
> >>> Hi,
> >>>
> >>> I am using VLC streaming (as a boardcaster) to Darwin.
> >>>
> >>> But when I use a video client (e.g. quicktime/vlc) to watch that
> stream
> >> by
> >>> hitting Darwin, I see a lot of green rectangles in the video in the
> >>> beginning. (see attached screen shot).
> >>>
> >>> Can you please tell me what is wrong? And how can i fix it?
> >> I suspect this is due to a missing key frame. The decoder just fills in
> >> the blank in that case. Which of course when missing the first keyframe
> >> can produce strange effects.
> >
> >
> > Jean-Paul,
> >
> > I am seeing the same 'green area' issue in the result mp4 file when  I
> use
> > VLC to transcode a flv file. Here is the parameter that I used for
> > transcoding:
> >
> >   ./vlc -vvv -I dummy ~/Desktop/video.flv --sout
> >
> '#transcode{vcodec=mp4v,vb=400,acodec=mpga,ab=128,audo-sync}:standard{access=file,
> > mux=mp4, dst=/home/herman/genvlc.mp4}'
> >
> > I think you are right in saying the 'green area' problem is caused by a
> > missing key frame.  I put
> > more debug print statement in my ffmpge+vlc code. And it did say 'first
> > frame is no keyframe' and i notice that the first frame passed to
> > MPV_frame_start is type 2 ( FF_P_TYPE , not 1 (FF_I_TYPE) that I
> expected).
>
> The only thing you can do is to get rid of the green area is to make
> sure the first frame is a key-frame (I_TYPE). In your case that would
> mean to dump all frames until the first key-frame is found.
>
> You could try to force this by modifying packetizer/mpeg4video.c to take
> an option "force-start-on-keyframe" (or something like that).



Jean-Paul,

After going thru the code more, I find out where in the vlc code drop the
first key frame.

It is dropped in this method:
Packetize ( decoder_t *p_dec, block_t **pp_block )

of the module/packetizer/copy.c

the reason it gets dropped is beause 'p_block->i_dts = 0' and the code in
Packetize() is like this:

   if( p_block->i_dts <= 0 )
    {
      msg_Dbg( p_dec, "need dts > 0 %d %d\n", p_block->i_dts,
p_block->i_buffer  );
        block_Release( p_block );

    msg_Dbg( p_dec, "done call packetize 2\n" );
        return NULL;
    }

Can you please tell me how can i fix this, or what causes the packet
(p_block)'s i_dts to be 0?

Thank you.



Gtz,
> Jean-Paul Saman.
>
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