We are not currently able to force mov_text subtitles by setting
-disposition:s:0 +forced or equivalent. By setting the forced flags in
movtextenc as specifid in
https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap3/qtff3.html
subtitles can be forced as expected in VLC and similar players.
Copy AVStream disposition to AVCodecContext and use to set
DISPLAY_FLAG_ALL_SAMPLES_FORCED in movtextenc.c.
Signed-off-by: facefunk <facef...@fcfnk.com>
---
fftools/ffmpeg_opt.c | 5 +++++
libavcodec/avcodec.h | 11 +++++++++++
libavcodec/movtextenc.c | 41 ++++++++++++++++++++++++++++++++++++++++-
3 files changed, 56 insertions(+), 1 deletion(-)
diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
index e08455478f..a7fa809859 100644
--- a/fftools/ffmpeg_opt.c
+++ b/fftools/ffmpeg_opt.c
@@ -2244,6 +2244,11 @@ static int set_dispositions(OutputFile *of,
AVFormatContext *ctx)
if (ret < 0)
return ret;
+
+ // For output streams, Set subtitle flags to forced when stream
+ // disposition is forced.
+ if(ost->enc_ctx && ost->st->disposition & AV_DISPOSITION_FORCED)
+ ost->enc_ctx->subtitle_flags |= AV_SUBTITLE_FLAG_FORCED;
}
} else {
// For each media type with more than one stream, find a suitable
stream to
diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index cb5c25bf63..182f452557 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -2054,6 +2054,17 @@ typedef struct AVCodecContext {
* The decoder can then override during decoding as needed.
*/
AVChannelLayout ch_layout;
+
+ /**
+ * Subtitle codecs only. Bit set of AV_SUBTITLE_FLAG_*.
+ *
+ * Some subtitle codecs may use this field to determine the subtitle
+ * display flags to encode.
+ *
+ * - encoding: set by user
+ * - decoding: unused
+ */
+ int subtitle_flags;
} AVCodecContext;
/**
diff --git a/libavcodec/movtextenc.c b/libavcodec/movtextenc.c
index 728338f2cc..bb6021f6d1 100644
--- a/libavcodec/movtextenc.c
+++ b/libavcodec/movtextenc.c
@@ -50,6 +50,40 @@
#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)
+/**
+ *
https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap3/qtff3.html
+ *
+ * Display flags
+ * A 32-bit integer containing flags that describe how the subtitle text should
+ * be drawn.
+ * The following flags are defined:
+ *
+ * Vertical placement
+ * Controls vertical placement of the subtitle text.
+ * If this flag is set, the subtitle media handler uses the top coordinate of
+ * the display bounds of the override 'tbox' text box to determine the
+ * subtitle’s vertical placement as described in Subtitle Track Header Size
+ * and Placement. Otherwise, the subtitle displays at the bottom of the video.
+ */
+#define DISPLAY_FLAG_VERTICAL_PLACEMENT_TOP 0x20000000
+
+/**
+ * Some samples are forced
+ * Indicates whether any subtitle samples contain forced atoms. If this flag is
+ * set, at least one sample contains a forced ('frcd') atom as described in
+ * Subtitle Sample Data.
+ */
+#define DISPLAY_FLAG_SOME_SAMPLES_FORCED 0x40000000
+
+/**
+ * All samples are forced
+ * If this flag is set, the subtitle media handler treats all samples as forced
+ * subtitles, regardless of the presence or absence of a 'frcd' atom.
+ * If this flag is set, the Some Samples Are Forced flag must also be set
+ * (making 0xC0000000).
+ */
+#define DISPLAY_FLAG_ALL_SAMPLES_FORCED 0x80000000
+
typedef struct {
uint16_t style_start;
uint16_t style_end;
@@ -183,6 +217,7 @@ static int encode_sample_description(AVCodecContext *avctx)
int font_names_total_len = 0;
MovTextContext *s = avctx->priv_data;
uint8_t buf[30], *p = buf;
+ uint32_t display_flags = 0;
// 0x00, 0x00, 0x00, 0x00, // uint32_t displayFlags
// 0x01, // int8_t horizontal-justification
@@ -241,7 +276,11 @@ static int encode_sample_description(AVCodecContext *avctx)
(255 - ((uint32_t)style->back_color >> 24));
}
- bytestream_put_be32(&p, 0); // displayFlags
+ if (avctx->subtitle_flags & AV_SUBTITLE_FLAG_FORCED)
+ display_flags = DISPLAY_FLAG_SOME_SAMPLES_FORCED |
+ DISPLAY_FLAG_ALL_SAMPLES_FORCED;
+
+ bytestream_put_be32(&p, display_flags); // displayFlags
bytestream_put_be16(&p, 0x01FF); // horizontal/vertical justification (2x
int8_t)
bytestream_put_be32(&p, back_color);
bytestream_put_be64(&p, 0); // BoxRecord - 4xint16_t: top, left, bottom,
right
--
2.25.1
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