FFMPEG El archivo SRT convertido de VTT tiene un problema de superposición de tiempo

Estoy usando FFMPEG para convertir el archivo VTT a SRT. Pero el archivo de salida tiene un problema de superposición. Necesito ayuda para solucionar este problema superpuesto

WEBVTT
Kind: captions
Language: en
Style:
::cue(c.colorCCCCCC) { color: rgb(204,204,204);
 }
::cue(c.colorE5E5E5) { color: rgb(229,229,229);
 }
##

00:00:06.160 --> 00:00:17.410 align:start position:19%
a<c.colorE5E5E5><00:00:08.280><c> kung</c><00:00:09.280><c> fu</c><00:00:09.309><c> master</c><00:00:11.340><c> he's</c><00:00:12.340><c> prepared</c></c><c.colorCCCCCC><00:00:12.940><c> to</c><00:00:13.180><c> train</c></c>

00:00:13.540 --> 00:00:28.230 align:start position:19%
hard<c.colorE5E5E5><00:00:15.600><c> move</c><00:00:16.600><c> fast</c></c>

00:00:17.410 --> 00:00:31.710 align:start position:19%
<c.colorCCCCCC>incoming</c><c.colorE5E5E5><00:00:18.400><c> be</c><00:00:18.910><c> brave</c><00:00:22.770><c> and</c><00:00:23.770><c> above</c><00:00:24.280><c> all</c></c><c.colorCCCCCC><00:00:26.730><c> be</c><00:00:27.730><c> ready</c></c>

00:00:28.230 --> 00:00:31.710 align:start position:19%
for<00:00:29.230><c> anything</c>

00:00:35.370 --> 00:00:47.829 align:start position:19%
perfect<c.colorE5E5E5><00:00:36.390><c> really</c></c><c.colorCCCCCC><00:00:37.390><c> know</c><00:00:38.249><c> again</c><00:00:40.739><c> but</c><00:00:41.739><c> next</c></c>

00:00:42.069 --> 00:00:50.969 align:start position:19%
January<c.colorE5E5E5><00:00:42.789><c> nothing</c><00:00:43.569><c> can</c><00:00:43.809><c> prepare</c><00:00:43.989><c> him</c><00:00:44.229><c> for</c><00:00:46.829><c> his</c></c>

00:00:47.829 --> 00:00:50.969 align:start position:19%
greatest<00:00:48.219><c> challenge</c><c.colorCCCCCC><00:00:48.519><c> yet</c></c>

00:00:52.720 --> 00:01:00.140 align:start position:19%
who<00:00:53.720><c> are</c><00:00:54.350><c> you</c><00:00:55.390><c> I'm</c><00:00:56.390><c> Li</c><00:00:56.900><c> Shan</c><c.colorE5E5E5><00:00:57.610><c> I'm</c><00:00:58.610><c> looking</c><00:00:59.300><c> for</c></c>

00:00:59.570 --> 00:01:08.840 align:start position:19%
my<00:00:59.780><c> son</c>

00:01:00.140 --> 00:01:13.300 align:start position:19%
<c.colorCCCCCC>oh</c><c.colorE5E5E5><00:01:03.610><c> you</c><00:01:04.610><c> lost</c><00:01:04.820><c> your</c><00:01:05.030><c> son</c><00:01:05.330><c> yes</c><00:01:06.640><c> many</c><00:01:07.640><c> years</c><00:01:08.570><c> ago</c></c>

00:01:08.840 --> 00:01:20.330 align:start position:19%
<c.colorE5E5E5>I<00:01:09.430><c> lost</c><00:01:10.430><c> my</c><00:01:10.550><c> father</c><00:01:11.170><c> I'm</c></c><c.colorCCCCCC><00:01:12.170><c> very</c><00:01:12.500><c> sorry</c></c>

00:01:13.300 --> 00:01:25.190 align:start position:19%
thank<00:01:14.300><c> you</c><00:01:17.110><c> well</c><00:01:18.729><c> good</c><00:01:19.729><c> luck</c><c.colorE5E5E5><00:01:19.760><c> to</c><00:01:20.030><c> you</c></c>

00:01:20.330 --> 00:01:28.720 align:start position:19%
<c.colorE5E5E5>you<00:01:21.320><c> too</c></c><c.colorCCCCCC><00:01:21.560><c> I</c><00:01:21.850><c> hope</c><00:01:22.850><c> you</c><00:01:22.970><c> find</c><00:01:23.150><c> your</c><00:01:23.270><c> son</c><00:01:23.390><c> and</c><00:01:24.190><c> I</c></c>

00:01:25.190 --> 00:01:28.720 align:start position:19%
hope<00:01:25.490><c> you</c><00:01:25.729><c> find</c><00:01:26.119><c> your</c><c.colorCCCCCC><00:01:26.300><c> father</c></c>

00:01:50.619 --> 00:01:52.679 align:start position:19%
<c.colorE5E5E5>you</c>

Archivo SRT convertido

1
00:00:06,160 --> 00:00:17,410
a kung fu master he's prepared to train

2
00:00:13,540 --> 00:00:28,230
hard move fast

3
00:00:17,410 --> 00:00:31,710
incoming be brave and above all be ready

4
00:00:28,230 --> 00:00:31,710
for anything

5
00:00:35,370 --> 00:00:47,829
perfect really know again but next

6
00:00:42,069 --> 00:00:50,969
January nothing can prepare him for his

7
00:00:47,829 --> 00:00:50,969
greatest challenge yet

8
00:00:52,720 --> 00:01:00,140
who are you I'm Li Shan I'm looking for

9
00:00:59,570 --> 00:01:08,840
my son

10
00:01:00,140 --> 00:01:13,300
oh you lost your son yes many years ago

11
00:01:08,840 --> 00:01:20,330
I lost my father I'm very sorry

12
00:01:13,300 --> 00:01:25,190
thank you well good luck to you

13
00:01:20,330 --> 00:01:28,720
you too I hope you find your son and I

14
00:01:25,190 --> 00:01:28,720
hope you find your father

15
00:01:50,619 --> 00:01:52,679
you

ver la superposición aquí

¡ACTUALIZAR!

ffmpeg puede hacerlo en tiempo de conversión con -fix_sub_duration opción.

desde man ffmpeg:

   -fix_sub_duration
       Fix subtitles durations. For each subtitle, wait for the next
       packet in the same stream and adjust the duration of the first to
       avoid overlap. This is necessary with some subtitles codecs,
       especially DVB subtitles, because the duration in the original
       packet is only a rough estimate and the end is actually marked by
       an empty subtitle frame. Failing to use this option when necessary
       can result in exaggerated durations or muxing failures due to non-
       monotonic timestamps.

   Note that this option will delay the output of all data until the
   next subtitle packet is decoded: it may increase memory consumption
   and latency a lot.