[FFmpeg-devel] [PATCH 23/23] lavc/movtextenc: add option to scale fontsize with height

[Philip Langdale]

On Mon, 6 Apr 2020 11:52:18 -0600
John Stebbins <jstebbins at jetheaddev.com> wrote:

> If the video dimensions are different than the ASS play_res then the
> font sizes need to be adjusted to get the same apparent render size.
> ---
>  libavcodec/movtextenc.c | 30 +++++++++++++++++++++++++++++-
>  1 file changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/movtextenc.c b/libavcodec/movtextenc.c
> index a62bdb7eb0..3d4371b180 100644
> --- a/libavcodec/movtextenc.c
> +++ b/libavcodec/movtextenc.c
> @@ -21,6 +21,7 @@
>  
>  #include <stdarg.h>
>  #include "avcodec.h"
> +#include "libavutil/opt.h"
>  #include "libavutil/avassert.h"
>  #include "libavutil/avstring.h"
>  #include "libavutil/intreadwrite.h"
> @@ -45,6 +46,7 @@
>  #define DEFAULT_STYLE_FLAG     0x00
>  
>  #define BGR_TO_RGB(c) (((c) & 0xff) << 16 | ((c) & 0xff00) | (((c)
> >> 16) & 0xff)) +#define FONTSIZE_SCALE(s,fs) ((fs) *
> >> (s)->font_scale_factor + 0.5)
>  #define av_bprint_append_any(buf, data, size)
> av_bprint_append_data(buf, ((const char*)data), size) 
>  typedef struct {
> @@ -66,6 +68,7 @@ typedef struct {
>  } HilightcolorBox;
>  
>  typedef struct {
> +    AVClass *class;
>      AVCodecContext *avctx;
>  
>      ASSSplitContext *ass_ctx;
> @@ -81,6 +84,8 @@ typedef struct {
>      uint16_t byte_count;
>      char ** fonts;
>      int font_count;
> +    double font_scale_factor;
> +    int frame_height;
>  } MovTextContext;
>  
>  typedef struct {
> @@ -236,6 +241,13 @@ static int
> encode_sample_description(AVCodecContext *avctx) 
>      // Populate sample description from ASS header
>      ass = ff_ass_get(s->ass_ctx);
> +    // Compute font scaling factor based on (optionally) provided
> +    // output video height and ASS script play_res_y
> +    if (s->frame_height && ass->script_info.play_res_y)
> +        s->font_scale_factor = (double)s->frame_height /
> ass->script_info.play_res_y;
> +    else
> +        s->font_scale_factor = 1;
> +
>      style = ff_ass_style_get(s->ass_ctx, "Default");
>      if (!style && ass->styles_count) {
>          style = &ass->styles[0];
> @@ -245,7 +257,7 @@ static int
> encode_sample_description(AVCodecContext *avctx) s->d.style_color
> = DEFAULT_STYLE_COLOR; s->d.style_flag     = DEFAULT_STYLE_FLAG;
>      if (style) {
> -        s->d.style_fontsize = style->font_size;
> +        s->d.style_fontsize = FONTSIZE_SCALE(s, style->font_size);
>          s->d.style_color = BGR_TO_RGB(style->primary_color &
> 0xffffff) << 8 | 255 - ((uint32_t)style->primary_color >> 24);
>          s->d.style_flag = (!!style->bold      * STYLE_FLAG_BOLD)   |
> @@ -530,6 +542,7 @@ static void mov_text_font_name_cb(void *priv,
> const char *name) 
>  static void mov_text_font_size_set(MovTextContext *s, int size)
>  {
> +    size = FONTSIZE_SCALE(s, size);
>      if (!s->style_attributes_temp ||
>          s->style_attributes_temp->style_fontsize == size) {
>          // color hasn't changed
> @@ -709,12 +722,27 @@ exit:
>      return length;
>  }
>  
> +#define OFFSET(x) offsetof(MovTextContext, x)
> +#define FLAGS AV_OPT_FLAG_ENCODING_PARAM | AV_OPT_FLAG_SUBTITLE_PARAM
> +static const AVOption options[] = {
> +    { "height", "Frame height, usually video height",
> OFFSET(frame_height), AV_OPT_TYPE_INT, {.i64=0}, 0, INT_MAX, FLAGS },
> +    { NULL },
> +};
> +
> +static const AVClass mov_text_encoder_class = {
> +    .class_name = "MOV text enoder",
> +    .item_name  = av_default_item_name,
> +    .option     = options,
> +    .version    = LIBAVUTIL_VERSION_INT,
> +};
> +
>  AVCodec ff_movtext_encoder = {
>      .name           = "mov_text",
>      .long_name      = NULL_IF_CONFIG_SMALL("3GPP Timed Text
> subtitle"), .type           = AVMEDIA_TYPE_SUBTITLE,
>      .id             = AV_CODEC_ID_MOV_TEXT,
>      .priv_data_size = sizeof(MovTextContext),
> +    .priv_class     = &mov_text_encoder_class,
>      .init           = mov_text_encode_init,
>      .encode_sub     = mov_text_encode_frame,
>      .close          = mov_text_encode_close,

LGTM.


--phil