[Libva] mpeg4 decoding

[Varga, Michael]

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;
>