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From: Ronan Waide <waider@waider.ie>
To: ffmpeg-devel@ffmpeg.org
Date: Mon, 21 Apr 2025 11:56:23 +0100
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Subject: [FFmpeg-devel] [PATCH v6] avcodec/dvbsubenc: add a disable_2bpp
option to work around some decoders.
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[rebasing against current HEAD since there were some conflicting changes]
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. Per suggestion from sw, disable_2pp defaults to true.
Signed-off-by: Ronan Waide <waider@waider.ie>
---
doc/encoders.texi | 27 +++++++++++++++++
libavcodec/dvbsubenc.c | 68 +++++++++++++++++++++++++++++++-----------
2 files changed, 77 insertions(+), 18 deletions(-)
diff --git a/doc/encoders.texi b/doc/encoders.texi
index 128e81a2e7..7dcf0d1f92 100644
--- a/doc/encoders.texi
+++ b/doc/encoders.texi
@@ -4497,6 +4497,33 @@ 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.
+
+@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. (default)
+@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 113bb320a9..5c02074484 100644
--- a/libavcodec/dvbsubenc.c
+++ b/libavcodec/dvbsubenc.c
@@ -22,9 +22,12 @@
#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;
} DVBSubtitleContext;
#define PUTBITS2(val)\
@@ -274,13 +277,15 @@ static int dvbsub_encode(AVCodecContext *avctx, uint8_t *outbuf, int buf_size,
{
DVBSubtitleContext *s = avctx->priv_data;
uint8_t *q, *pseg_len;
- int page_id, region_id, clut_id, object_id, i, bpp_index, page_state;
+ int page_id, region_id, clut_id, object_id, i, bpp_index, page_state, min_colors;
q = outbuf;
page_id = 1;
+ min_colors = s->disable_2bpp ? 16 : 0;
+
if (h->num_rects && !h->rects)
return AVERROR(EINVAL);
@@ -330,21 +335,22 @@ 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++) {
/* CLUT segment */
+ int nb_colors = FFMAX(min_colors, h->rects[clut_id]->nb_colors);
- if (h->rects[clut_id]->nb_colors <= 4U) {
+ if (nb_colors <= 4U) {
/* 2 bpp, some decoders do not support it correctly */
bpp_index = 0;
- } else if (h->rects[clut_id]->nb_colors <= 16U) {
+ } else if (nb_colors <= 16U) {
/* 4 bpp, standard encoding */
bpp_index = 1;
- } else if (h->rects[clut_id]->nb_colors <= 256U) {
+ } else if (nb_colors <= 256U) {
/* 8 bpp, standard encoding */
bpp_index = 2;
} else {
return AVERROR(EINVAL);
}
- if (buf_size < 6 + h->rects[clut_id]->nb_colors * 6)
+ if (buf_size < 6 + nb_colors * 6)
return AVERROR_BUFFER_TOO_SMALL;
/* CLUT segment */
@@ -356,16 +362,24 @@ 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);
@@ -375,7 +389,7 @@ 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)
@@ -383,14 +397,15 @@ 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 = FFMAX(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 {
@@ -426,17 +441,19 @@ 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 = FFMAX(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 {
@@ -508,6 +525,20 @@ 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 = 1}, 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"),
@@ -515,4 +546,5 @@ const FFCodec ff_dvbsub_encoder = {
.p.id = AV_CODEC_ID_DVB_SUBTITLE,
.priv_data_size = sizeof(DVBSubtitleContext),
FF_CODEC_ENCODE_SUB_CB(dvbsub_encode),
+ .p.priv_class = &dvbsubenc_class,
};
--
2.39.5 (Apple Git-154)
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