Re: [xine-devel] New decoder/video output module

[Miguel F. <mi...@ce...>]

On Fri, 2002-08-09 at 09:03, Hamish Guthrie wrote:
> The issue I have noticed is that in xine-engine/video_out.c, there is code
> which retrieves the number of frame buffers from the driver, then sets
> num_frame_buffers to that value (in my case 4 because I only have 4 decode
> buffers), or 5, whichever is the greater. If I modify this code so that it
> will accept 4 as the minimum number of frame buffers, I get a lot of errors
> from the decoder such as: dropping b-frame because ref is bad (fw ref frame
> 0, bad 1;bw ref frame 1, bad 1).
> 
> I have not looked into the logic behind frame re-ordering and fwd/back
> referencing yet, but wondered if the algorithm used has a limitation to a
> minimum of 5 frames?

Difficult question, since we don't know exactly what have you changed.
The minimum of 5 frames is needed to prevent xine from doing weird
things like blending overlay in a frame that was still needed as
reference frame.

For instance one frame is hold at video out driver to do the snapshot
function, so if this is a critical thing you may try removing these
lines from video_out.c:

  /* hold current frame for snapshot feature */
  if( this->last_frame ) {
    vo_frame_dec_lock( this->last_frame );
  }
  vo_frame_inc_lock( img );
  this->last_frame = img;

i'm not sure if it will help you thought. changes are you will really
need to check why ref frame is bad. i guess you are working over our
libmpeg2 plugin, and if i remember correctly every frame is "bad" until
it gets completely decoded.

btw, is this thing a commercial product or something?

regards,

Miguel