[Libva] mpeg4 decoding

[Xiang, Haihao]

Hi Michael,

 I am not familiar with MPEG4, I think modulo_time_base is used to
calculate time stamp etc, is modulo_time_base really required for HW
decode ?

Thanks
Haihao

> I only really need modulo_time_base. It would appear from my tests vop_time_increment is not needed. Could modulo_time_base be added?
> 
> The core issue I am having is I need the modulo_time_base value. I noticed Gwenole wrote a reference driver which wraps vdpau. Gwenole's code has a fix to compute modulo_time_base. I cannot use code from Gwenole's driver due to licensing issues, his code is GPL and MESA is MIT.
> 
> -----Original Message-----
> From: Emil Velikov [mailto:emil.l.velikov at gmail.com] 
> Sent: Saturday, November 08, 2014 9:58 AM
> To: Varga, Michael; Gwenole Beauchesne
> Cc: emil.l.velikov at gmail.com; libva at lists.freedesktop.org
> Subject: Re: [Libva] mpeg4 decoding
> 
> Hi guys.
> 
> Don't mean to be picky or anything but won't this change cause a non-backward compat ABI/API breakage ?
> 
> While adding modulo_time_base might be ok (highly dependant on the implementation which may use the vop_fields union without sanitising it), vop_time_increment is definitely going to cause issues.
> 
> 
> Cheers,
> Emil
> 
> On 31/10/14 14:32, Varga, Michael wrote:
> > Hi Gwenole,
> > 
> > I double checked vop_time_increment and its not strictly needed, 
> > setting this value to 0 works but if you'll add it I'll use anyway. My 
> > patch is below. I declared modulo_time_base with 4 bits, the MPEG4 
> > spec does not specify an upper bound for the size of this variable. If 
> > you think this is too big I can reduce it. Also, is there anything you 
> > think I should know about your process for submitting patches? Thanks! 
> > :)
> > 
> > 
> > From 44aeb5d81789c42404d6a2398ef06699aabc6d73 Mon Sep 17 00:00:00 2001
> > From: Michael Varga <Michael.Varga at amd.com>
> > Date: Fri, 31 Oct 2014 08:58:34 -0500
> > Subject: [PATCH] va: added two variables to 
> > VAPictureParameterBufferMPEG4
> > 
> > Added modulo_time_base and vop_time_increment so the VOP header may be 
> > reconstructed if it has been truncated.
> > 
> > Signed-off-by: Michael Varga <Michael.Varga at amd.com>
> > ---
> >  va/va.h | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/va/va.h b/va/va.h
> > index 01694a9..c21770c 100644
> > --- a/va/va.h
> > +++ b/va/va.h
> > @@ -1312,12 +1312,14 @@ typedef struct _VAPictureParameterBufferMPEG4
> >              unsigned int intra_dc_vlc_thr              : 3; 
> >              unsigned int top_field_first               : 1; 
> >              unsigned int alternate_vertical_scan_flag  : 1;
> > +            unsigned int modulo_time_base              : 4;
> >          } bits;
> >          unsigned int value;
> >      } vop_fields;
> >      unsigned char vop_fcode_forward;
> >      unsigned char vop_fcode_backward;
> >      unsigned short vop_time_increment_resolution;
> > +    unsigned short vop_time_increment;
> >      /* short header related */
> >      unsigned char num_gobs_in_vop;
> >      unsigned char num_macroblocks_in_gob;
> > 
> 
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