> On 1 Mar 2025, at 14:10, Ronan Waide <wai...@waider.ie> wrote:
>
> (changes from previous attempt: fixed an error in the docfile and made sure
> I'm diffing against origin/master)
>
> As noted in the code in several places, some DVB subtitle decoders
> don't handle 2bpp color. This patch adds a disable_2bpp option which
> disables the 2bpp format; subtitles which would use 2bpp will be bumped
> up to 4bpp.
>
> Signed-off-by: Ronan Waide <wai...@waider.ie>
> ---
> doc/encoders.texi | 27 ++++++++++++++
> libavcodec/dvbsubenc.c | 85 +++++++++++++++++++++++++++++++++---------
> 2 files changed, 95 insertions(+), 17 deletions(-)
>
> diff --git a/doc/encoders.texi b/doc/encoders.texi
> index f3fcc1aa60..07984b6b54 100644
> --- a/doc/encoders.texi
> +++ b/doc/encoders.texi
> @@ -4484,6 +4484,33 @@ Reduces detail but attempts to preserve color at
> extremely low bitrates.
> @chapter Subtitles Encoders
> @c man begin SUBTITLES ENCODERS
>
> +@section dvbsub
> +
> +This codec encodes the bitmap subtitle format that is used in DVB
> +broadcasts and recordings. The bitmaps are typically embedded in a
> +container such as MPEG-TS as a separate stream.
> +
> +@subsection Options
> +
> +@table @option
> +@item disable_2bpp @var{boolean}
> +Disable the 2 bits-per-pixel encoding format.
> +
> +DVB supports 2, 4, and 8 bits-per-pixel color lookup tables. However,
> +not all players support or properly support 2 bits-per-pixel,
> +resulting in unusable subtitles.
> +@table @option
> +@item 0
> +The 2 bits-per-pixel encoding format will be used for subtitles with 4
> +colors or less. (default)
> +
> +@item 1
> +The 2 bits-per-pixel encoding format will be disabled, and subtitles
> +with 4 colors or less will use a 4 bits-per-pixel format.
> +@end table
> +
> +@end table
> +
> @section dvdsub
>
> This codec encodes the bitmap subtitle format that is used in DVDs.
> diff --git a/libavcodec/dvbsubenc.c b/libavcodec/dvbsubenc.c
> index 822e3a5309..727a75e901 100644
> --- a/libavcodec/dvbsubenc.c
> +++ b/libavcodec/dvbsubenc.c
> @@ -22,9 +22,13 @@
> #include "bytestream.h"
> #include "codec_internal.h"
> #include "libavutil/colorspace.h"
> +#include "libavutil/opt.h"
>
> typedef struct DVBSubtitleContext {
> + AVClass * class;
> int object_version;
> + int disable_2bpp;
> + int min_colors;
> } DVBSubtitleContext;
>
> #define PUTBITS2(val)\
> @@ -38,6 +42,18 @@ typedef struct DVBSubtitleContext {
> }\
> }
>
> +static int dvbsub_init(AVCodecContext *avctx)
> +{
> + DVBSubtitleContext *s = avctx->priv_data;
> + if (s->disable_2bpp) {
> + av_log(avctx, AV_LOG_DEBUG, "Disabling 2bpp subtitles.\n");
> + s->min_colors = 16;
> + } else {
> + s->min_colors = 0;
> + }
> + return 0;
> +}
> +
> static int dvb_encode_rle2(uint8_t **pq, int buf_size,
> const uint8_t *bitmap, int linesize,
> int w, int h)
> @@ -326,18 +342,22 @@ static int dvbsub_encode(AVCodecContext *avctx, uint8_t
> *outbuf, int buf_size,
>
> if (h->num_rects) {
> for (clut_id = 0; clut_id < h->num_rects; clut_id++) {
> - if (buf_size < 6 + h->rects[clut_id]->nb_colors * 6)
> + int nb_colors = s->min_colors > h->rects[clut_id]->nb_colors
> + ? s->min_colors
> + : h->rects[clut_id]->nb_colors;
> +
> + if (buf_size < 6 + nb_colors * 6)
> return AVERROR_BUFFER_TOO_SMALL;
>
> /* CLUT segment */
>
> - if (h->rects[clut_id]->nb_colors <= 4) {
> + if (nb_colors <= 4) {
> /* 2 bpp, some decoders do not support it correctly */
> bpp_index = 0;
> - } else if (h->rects[clut_id]->nb_colors <= 16) {
> + } else if (nb_colors <= 16) {
> /* 4 bpp, standard encoding */
> bpp_index = 1;
> - } else if (h->rects[clut_id]->nb_colors <= 256) {
> + } else if (nb_colors <= 256) {
> /* 8 bpp, standard encoding */
> bpp_index = 2;
> } else {
> @@ -354,16 +374,24 @@ static int dvbsub_encode(AVCodecContext *avctx, uint8_t
> *outbuf, int buf_size,
> *q++ = clut_id;
> *q++ = (0 << 4) | 0xf; /* version = 0 */
>
> - for(i = 0; i < h->rects[clut_id]->nb_colors; i++) {
> + for(i = 0; i < nb_colors; i++) {
> *q++ = i; /* clut_entry_id */
> *q++ = (1 << (7 - bpp_index)) | (0xf << 1) | 1; /* 2
> bits/pixel full range */
> {
> int a, r, g, b;
> - uint32_t x= ((uint32_t*)h->rects[clut_id]->data[1])[i];
> - a = (x >> 24) & 0xff;
> - r = (x >> 16) & 0xff;
> - g = (x >> 8) & 0xff;
> - b = (x >> 0) & 0xff;
> + if (i < h->rects[clut_id]->nb_colors) {
> + uint32_t x=
> ((uint32_t*)h->rects[clut_id]->data[1])[i];
> + a = (x >> 24) & 0xff;
> + r = (x >> 16) & 0xff;
> + g = (x >> 8) & 0xff;
> + b = (x >> 0) & 0xff;
> + } else {
> + /* pad out the CLUT */
> + a = 0;
> + r = 0;
> + g = 0;
> + b = 0;
> + }
>
> *q++ = RGB_TO_Y_CCIR(r, g, b);
> *q++ = RGB_TO_V_CCIR(r, g, b, 0);
> @@ -373,7 +401,7 @@ static int dvbsub_encode(AVCodecContext *avctx, uint8_t
> *outbuf, int buf_size,
> }
>
> bytestream_put_be16(&pseg_len, q - pseg_len - 2);
> - buf_size -= 6 + h->rects[clut_id]->nb_colors * 6;
> + buf_size -= 6 + nb_colors * 6;
> }
>
> if (buf_size < h->num_rects * 22)
> @@ -381,14 +409,17 @@ static int dvbsub_encode(AVCodecContext *avctx, uint8_t
> *outbuf, int buf_size,
> for (region_id = 0; region_id < h->num_rects; region_id++) {
>
> /* region composition segment */
> + int nb_colors = s->min_colors > h->rects[region_id]->nb_colors
> + ? s->min_colors
> + : h->rects[region_id]->nb_colors;
>
> - if (h->rects[region_id]->nb_colors <= 4) {
> + if (nb_colors <= 4) {
> /* 2 bpp, some decoders do not support it correctly */
> bpp_index = 0;
> - } else if (h->rects[region_id]->nb_colors <= 16) {
> + } else if (nb_colors <= 16) {
> /* 4 bpp, standard encoding */
> bpp_index = 1;
> - } else if (h->rects[region_id]->nb_colors <= 256) {
> + } else if (nb_colors <= 256) {
> /* 8 bpp, standard encoding */
> bpp_index = 2;
> } else {
> @@ -424,17 +455,21 @@ static int dvbsub_encode(AVCodecContext *avctx, uint8_t
> *outbuf, int buf_size,
> const uint8_t *bitmap, int linesize,
> int w, int h);
>
> + int nb_colors = s->min_colors > h->rects[object_id]->nb_colors
> + ? s->min_colors
> + : h->rects[object_id]->nb_colors;
> +
> if (buf_size < 13)
> return AVERROR_BUFFER_TOO_SMALL;
>
> /* bpp_index maths */
> - if (h->rects[object_id]->nb_colors <= 4) {
> + if (nb_colors <= 4) {
> /* 2 bpp, some decoders do not support it correctly */
> dvb_encode_rle = dvb_encode_rle2;
> - } else if (h->rects[object_id]->nb_colors <= 16) {
> + } else if (nb_colors <= 16) {
> /* 4 bpp, standard encoding */
> dvb_encode_rle = dvb_encode_rle4;
> - } else if (h->rects[object_id]->nb_colors <= 256) {
> + } else if (nb_colors <= 256) {
> /* 8 bpp, standard encoding */
> dvb_encode_rle = dvb_encode_rle8;
> } else {
> @@ -506,6 +541,20 @@ static int dvbsub_encode(AVCodecContext *avctx, uint8_t
> *outbuf, int buf_size,
> return q - outbuf;
> }
>
> +#define OFFSET(x) offsetof(DVBSubtitleContext, x)
> +#define SE AV_OPT_FLAG_SUBTITLE_PARAM | AV_OPT_FLAG_ENCODING_PARAM
> +static const AVOption options[] = {
> + {"disable_2bpp", "disable the 2bpp subtitle encoder",
> OFFSET(disable_2bpp), AV_OPT_TYPE_BOOL, {.i64 = 0}, 0, 1, SE},
> + { NULL },
> +};
> +
> +static const AVClass dvbsubenc_class = {
> + .class_name = "DVBSUB subtitle encoder",
> + .item_name = av_default_item_name,
> + .option = options,
> + .version = LIBAVUTIL_VERSION_INT,
> +};
> +
> const FFCodec ff_dvbsub_encoder = {
> .p.name = "dvbsub",
> CODEC_LONG_NAME("DVB subtitles"),
> @@ -513,4 +562,6 @@ const FFCodec ff_dvbsub_encoder = {
> .p.id = AV_CODEC_ID_DVB_SUBTITLE,
> .priv_data_size = sizeof(DVBSubtitleContext),
> FF_CODEC_ENCODE_SUB_CB(dvbsub_encode),
> + .init = dvbsub_init,
> + .p.priv_class = &dvbsubenc_class,
> };
> --
> 2.39.5 (Apple Git-154)
>
This failed again, and I see the problem - I'm diffing against
https://github.com/FFmpeg/FFmpeg.git rather than
https://git.ffmpeg.org/ffmpeg.git. Apologies for the confusion on my part.
Fixed fix of a fix incoming...
Cheers,
Waider.
--
Ronan Waide
wai...@waider.ie
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