Re: [FFmpeg-devel] [PATCH] dvbsubenc: add a disable_2bpp option to work around some decoders.

[Ronan Waide <waider@waider.ie>]

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 <waider@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)





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