[FFmpeg-trac] #6021(avcodec:closed): tx3g / mov_text subtitles are not encoded correctly in some specific cases
FFmpeg
trac at avcodec.org
Sat Apr 6 01:28:36 EEST 2019
#6021: tx3g / mov_text subtitles are not encoded correctly in some specific cases
---------------------------------------+-----------------------------------
Reporter: erikbs | Owner:
Type: defect | Status: closed
Priority: normal | Component: avcodec
Version: git-master | Resolution: fixed
Keywords: utf8 mov_text | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
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Comment (by CoRoNe):
> ''I discovered that MP4Box writes a subtitle box size while ffmpeg does
not (or, more precisely, it apparently sets the box size to 0x0). Perhaps
that is why the subtitles are not shown on the TV?
Do you have a patch for this by any chance? I'm not a hero with C/C++.''
\\
> ''...demux and remux''
This works. My tv renders the subtitles perfectly. So I'm guessing
something is going wrong with the muxing process.
Comparing the 2 mp4-files in MediaInfo I noticed the one created by FFmpeg
mentioning "'''Muxing mode: sbtl'''" and "'''Alternate group: 3'''", where
as the one created by MP4Box does not.
And for everyone's info:
{{{
--- VPWON_1269922-t32_MP4Box.ttxt 2019-04-05 23:33:21.500000000
+0200
+++ VPWON_1269922-t32_FFmpeg_demux-MP4Box.ttxt 2019-04-05
23:16:37.475016000 +0200
@@ -1,12 +1,12 @@
<?xml version="1.0" encoding="UTF-8" ?>
<!-- GPAC 3GPP Text Stream -->
<TextStream version="1.1">
-<TextStreamHeader width="400" height="60" layer="0" translation_x="0"
translation_y="0">
+<TextStreamHeader width="0" height="0" layer="0" translation_x="0"
translation_y="0">
<TextSampleDescription horizontalJustification="center"
verticalJustification="bottom" backColor="0
0 0 0" verticalText="no" fillTextRegion="no" continuousKaraoke="no"
scroll="None">
<FontTable>
<FontTableEntry fontName="Serif" fontID="1"/>
</FontTable>
-<TextBox top="0" left="0" bottom="60" right="400"/>
+<TextBox top="0" left="0" bottom="0" right="0"/>
<Style styles="Normal" fontID="1" fontSize="18" color="ff ff ff ff"/>
</TextSampleDescription>
</TextStreamHeader>
}}}
This appears to be the only output difference between MP4Box's and
FFmpeg's tx3g encoder.
'//VPWON_1269922-t32_MP4Box.ttxt//': `mp4box -ttxt
"VPWON_1269922-t32.srt"`
'//VPWON_1269922-t32_FFmpeg_demux-MP4Box.ttxt//': `mp4box -ttxt 3
"VPWON_1269922(FFMpeg-mux_t32).mp4"`
--
Ticket URL: <https://trac.ffmpeg.org/ticket/6021#comment:19>
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