Ok, I seem to have a partial solution.
I thought that the place to put this would be in the dvdsubenc.c. So I made the
following changes (sorry for inline patch)
diff --git a/libavcodec/dvdsubenc.c b/libavcodec/dvdsubenc.c
index 425f0af..7cae3f4 100644
--- a/libavcodec/dvdsubenc.c
+++ b/libavcodec/dvdsubenc.c
@@ -30,6 +30,7 @@ typedef struct {
AVClass *class;
uint32_t global_palette[16];
int even_rows_fix;
+ int only_enc_forced;
} DVDSubtitleContext;
// ncnt is the nibble counter
@@ -277,6 +278,9 @@ static int encode_dvd_subtitles(AVCodecContext *avctx,
forced = 1;
break;
}
+ if (!forced && dvdc->only_enc_forced)
+ return 0;
+
vrect = *h->rects[0];
if (rects > 1) {
@@ -453,6 +457,7 @@ static int dvdsub_encode(AVCodecContext *avctx,
#define SE AV_OPT_FLAG_SUBTITLE_PARAM | AV_OPT_FLAG_ENCODING_PARAM
static const AVOption options[] = {
{"even_rows_fix", "Make number of rows even (workaround for some
players)", OFFSET(even_rows_fix), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 1, SE},
+ {"only_enc_forced", "Only encode forced subtitles",
OFFSET(only_enc_forced), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 1, SE},
{ NULL },
};
Ok, with this change, ffmpeg compiles fine. To do my testing, I have a file
called subs.mkv that just has two subtitle tracks. Both tracks have about 1000
subtitles. Track 0 has 46 forced subtitles, and track 1 has zero.
The commands I am using are
ffmpeg -i subs.mkv -map 0 -c:s dvdsub -only_enc_forced 1 only.mkv
This produces a smaller file. (from 7.9M to 240K)
If I pull out the subs & idx's using
mkvextract tracks rec.mkv 0:subs-0.sub 1:subs-1.sub produces strange results.
The idx's are the same size (49K & 61K) as the original idx's, but the .sub
files are smaller (2.3M & 2.8M from 4.9M and 5.5M)
However, something isn't right. If I try to open these new sub/idx's in
BDsup2sub I get: "ERROR: Invalid control buffer size"
However, if I put the only.mkv through ffmpeg again with:
ffmpeg -i only.mkv -map 0 -c:s dvdsub recode.mkv
And then pull the mkv's out with similar mkvextract command, it get the 46 (in
0) and 0 (in 1) subtitles I was expecting.
The file sizes are also saner (idx's 2.2K & 219B, .subs 184K and 0B)
So, it seems like what I am doing produces a mangled dvdsub track, but one that
ffmpeg can make sense of. It isn't just some muxing thing since if I run
only.mkv through mkvmerge, it doesn't get fixed.
How can I finish this patch?
-Nick
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