[vlc-devel] [PATCH] MP4: Parse transformation matrix

[Rémi Denis-Courmont]

On Thu, 12 Jan 2012 10:51:35 +0530, Gaurav Narula <gnarula94 at gmail.com>
wrote:
> +/* convert 16.16 fixed point to floating point */
> +static double conv_fx( int32_t fx ) {
> +    double fp = fx;
> +    fp /= 65536.;
> +    return fp;
> +}
> +

That's a lot of code to divide by 65536.

>  /* some functions for mp4 encoding of variables */
>  #ifdef MP4_VERBOSE
>  static void MP4_ConvertDate2Str( char *psz, uint64_t i_date )
> @@ -637,12 +645,31 @@ static int MP4_ReadBox_tkhd(  stream_t *p_stream,
> MP4_Box_t *p_box )
>      MP4_GET4BYTES( p_box->data.p_tkhd->i_width );
>      MP4_GET4BYTES( p_box->data.p_tkhd->i_height );
>  
> +    double rotation;    //angle in degrees to be rotated clockwise
> +    double scale[2];    // scale factor; sx = scale[0] , sy = scale[1]
> +    double translate[2];// amount to translate; tx = translate[0] , ty
=
> translate[1]
> +    
> +    int *matrix = p_box->data.p_tkhd->i_matrix;
> +    
> +    translate[0] = conv_fx(matrix[6]);
> +    translate[1] = conv_fx(matrix[7]);
> +    
> +    scale[0] = sqrt(conv_fx(matrix[0]) * conv_fx(matrix[0]) +
> +                    conv_fx(matrix[3]) * conv_fx(matrix[3]));
> +    scale[1] = sqrt(conv_fx(matrix[1]) * conv_fx(matrix[1]) +
> +                    conv_fx(matrix[4]) * conv_fx(matrix[4]));
> +    
> +    rotation = atan2(conv_fx(matrix[1]) / scale[1], conv_fx(matrix[0])
/
> scale[0]) * 180 / M_PI;
> +    
> +    if (rotation < 0)
> +        rotation += 360.;
> +

Do we really need all that trigonometry here? If it really is needed, then
linking will fail as is.

I would hope we could use transform (as for EXIF) rather than rotate.

>  #ifdef MP4_VERBOSE
>      MP4_ConvertDate2Str( s_creation_time,
>      p_box->data.p_mvhd->i_creation_time );
>      MP4_ConvertDate2Str( s_modification_time,
>      p_box->data.p_mvhd->i_modification_time );
>      MP4_ConvertDate2Str( s_duration, p_box->data.p_mvhd->i_duration );
>  
> -    msg_Dbg( p_stream, "read box: \"tkhd\" creation %s modification %s
> duration %s track ID %d layer %d volume %f width %f height %f. "
> +    msg_Dbg( p_stream, "read box: \"tkhd\" creation %s modification %s
> duration %s track ID %d layer %d volume %f rotation %f scaleX %f scaleY
%f
> translateX %f translateY %f width %f height %f. "
>              "Matrix: %i %i %i %i %i %i %i %i %i",
>                    s_creation_time,
>                    s_modification_time,
> @@ -650,6 +677,11 @@ static int MP4_ReadBox_tkhd(  stream_t *p_stream,
> MP4_Box_t *p_box )
>                    p_box->data.p_tkhd->i_track_ID,
>                    p_box->data.p_tkhd->i_layer,
>                    (float)p_box->data.p_tkhd->i_volume / 256 ,
> +                  rotation,
> +                  scale[0],
> +                  scale[1],
> +                  translate[0],
> +                  translate[1],
>                    (float)p_box->data.p_tkhd->i_width / 65536,
>                    (float)p_box->data.p_tkhd->i_height / 65536,
>                    p_box->data.p_tkhd->i_matrix[0],

-- 
Rémi Denis-Courmont
http://www.remlab.net/