[FFmpeg-devel] [PATCH] Use tkhd matrix for proper display in mov

[Michael Niedermayer]

On Fri, May 23, 2008 at 03:31:24PM -0400, John Schmiederer wrote:
> Hello all,
> 
> Attached is a patch to account for the transformation matrix contained in the tkhd atom for proper display width/height.
> 
> The video
> http://samples.mplayerhq.hu/mov/tkhd_matrix/white_zombie_scrunch.mov
> plays at 160x240 when it should really be scaled to 320x240.
> 
> 
> -John

Content-Description: ff_mov_tkhd_matrix.diff
> Index: libavformat/mov.c
> ===================================================================
> --- libavformat/mov.c	(revision 13266)
> +++ libavformat/mov.c	(working copy)
> @@ -1371,6 +1371,11 @@
>  
>  static int mov_read_tkhd(MOVContext *c, ByteIOContext *pb, MOV_atom_t atom)
>  {
> +    int i;
> +    int width;
> +    int height;
> +    float disp_transform[3];
> +    float display_matrix[3][3];

please use integers, there is no need for floats.


>      AVStream *st = c->fc->streams[c->fc->nb_streams-1];
>      int version = get_byte(pb);
>  
> @@ -1402,12 +1407,38 @@
>      get_be16(pb); /* volume */
>      get_be16(pb); /* reserved */
>  
> -    url_fskip(pb, 36); /* display matrix */
> +    //read in the display matrix (outlined in ISO 14496-12, Section 6.2.2)
> +    display_matrix[0][0] = (float)get_be32(pb)/(1<<16); //a
> +    display_matrix[0][1] = (float)get_be32(pb)/(1<<16); //b
> +    display_matrix[0][2] = (float)get_be32(pb)/(1<<30); //u
> +    display_matrix[1][0] = (float)get_be32(pb)/(1<<16); //c
> +    display_matrix[1][1] = (float)get_be32(pb)/(1<<16); //d
> +    display_matrix[1][2] = (float)get_be32(pb)/(1<<30); //v
> +    display_matrix[2][0] = (float)get_be32(pb)/(1<<16); //x
> +    display_matrix[2][1] = (float)get_be32(pb)/(1<<16); //y
> +    display_matrix[2][2] = (float)get_be32(pb)/(1<<30); //z

for(i=0; i<3; i++)

(and this loop can be merged with the next)


> +    

trailing whitespace is forbidden in svn


> +    width = get_be32(pb);  /* track width */
> +    height = get_be32(pb); /* track height */
> +    
> +    //transform the display width/height according to the matrix 
> +    if (width && height) {
> +      for (i=0; i<3; i++)
> +        disp_transform[i] = 
> +          width * display_matrix[0][i] +
> +          height * display_matrix[1][i] +
> +          display_matrix[2][i];
> +      disp_transform[0] /= disp_transform[2];
> +      disp_transform[1] /= disp_transform[2];
>  
> +      //the sample aspect ratio is new width/height divided by old width/height
> +      av_reduce(&st->codec->sample_aspect_ratio.num, 
> +        &st->codec->sample_aspect_ratio.den,
> +        disp_transform[0] * height, 
> +        disp_transform[1] * width,
> +        INT_MAX);        

dividing both by disp_transform[2] does not change the value thus it is
useless.


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

It is dangerous to be right in matters on which the established authorities
are wrong. -- Voltaire
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