The 3GPP Timed Text (TTXT / tx3g / mov_text) specification counts multibyte
UTF-8 characters as one single character, ffmpeg currently counts bytes. This
produces files where style boxes have incorrect offsets. This patch introduces:
1. a separate variable that keeps track of the byte count
2. a for loop that excludes continuation bytes from the character counting
Fixes trac #6021 (encoding part).
---
libavcodec/movtextenc.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/libavcodec/movtextenc.c b/libavcodec/movtextenc.c
index 20e01e2..8d09ff4 100644
--- a/libavcodec/movtextenc.c
+++ b/libavcodec/movtextenc.c
@@ -70,6 +70,7 @@ typedef struct {
uint8_t style_fontsize;
uint32_t style_color;
uint16_t text_pos;
+ uint16_t byte_size;
} MovTextContext;
typedef struct {
@@ -302,7 +303,10 @@ static void mov_text_text_cb(void *priv, const char *text,
int len)
{
MovTextContext *s = priv;
av_bprint_append_data(&s->buffer, text, len);
- s->text_pos += len;
+ for (int i = 0; i < len; i++)
+ if ((text[i] & 0xC0) != 0x80)
+ s->text_pos++; /* increase character count */
+ s->byte_size += len; /* increase byte count */
}
static void mov_text_new_line_cb(void *priv, int forced)
@@ -310,6 +314,7 @@ static void mov_text_new_line_cb(void *priv, int forced)
MovTextContext *s = priv;
av_bprint_append_data(&s->buffer, "\n", 1);
s->text_pos += 1;
+ s->byte_size += 1;
}
static const ASSCodesCallbacks mov_text_callbacks = {
@@ -328,6 +333,7 @@ static int mov_text_encode_frame(AVCodecContext *avctx,
unsigned char *buf,
size_t j;
s->text_pos = 0;
+ s->byte_size = 0;
s->count = 0;
s->box_flags = 0;
s->style_entries = 0;
@@ -362,7 +368,7 @@ static int mov_text_encode_frame(AVCodecContext *avctx,
unsigned char *buf,
}
}
- AV_WB16(buf, s->text_pos);
+ AV_WB16(buf, s->byte_size);
buf += 2;
if (!av_bprint_is_complete(&s->buffer)) {
--
1.9.5 (Apple Git-50.3)
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