Can't extract webvtt subtitle with ffmpeg

[[ss]vegeta]

Hello
I use the latest ffmpeg build from gyan.dev
I work with this file
https://we.tl/t-6rf39WxTdr

Mediainfo of the file

General
Unique ID                                : 215279765631081562880634938187970006669 (0xA1F55FECA9FE48198405F78428484E8D)
Complete name                            : C:\Users\User\Desktop\probaaa\a.mkv
Format                                   : Matroska
Format version                           : Version 4
File size                                : 113 MiB
Duration                                 : 7 min 24 s
Overall bit rate                         : 2 135 kb/s
Encoded date                             : UTC 2021-02-17 18:52:41
Writing application                      : mkvmerge v49.0.0 ('Sick Of Losing Soulmates') 64-bit
Writing library                          : libebml v1.4.0 + libmatroska v1.6.1

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : Main@L3.1
Format settings                          : CABAC / 4 Ref Frames
Format settings, CABAC                   : Yes
Format settings, Reference frames        : 4 frames
Codec ID                                 : V_MPEG4/ISO/AVC
Duration                                 : 7 min 23 s
Bit rate                                 : 2 008 kb/s
Width                                    : 1 280 pixels
Height                                   : 720 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 30.000 FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.073
Stream size                              : 106 MiB (94%)
Default                                  : Yes
Forced                                   : No
Color range                              : Limited
Color primaries                          : BT.709
Transfer characteristics                 : BT.709
Matrix coefficients                      : BT.709

Audio
ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : A_AAC-2
Duration                                 : 7 min 23 s
Bit rate                                 : 128 kb/s
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 SPF)
Compression mode                         : Lossy
Stream size                              : 6.77 MiB (6%)
Language                                 : English
Default                                  : Yes
Forced                                   : No

Text
ID                                       : 3
Format                                   : S_TEXT/WEBVTT
Codec ID                                 : S_TEXT/WEBVTT
Duration                                 : 7 min 24 s
Bit rate                                 : 141 b/s
Count of elements                        : 149
Stream size                              : 7.69 KiB (0%)
Language                                 : English
Default                                  : No
Forced                                   : No

From googling, I found out this should be the correct code

ffmpeg.exe -c:s webvtt -i a.mkv bla.vtt

But I keep getting
Unknown/unsupported AVCodecID S_TEXT/WEBVTT

I can't see anything wrong with the mkv header...

[[ss]vegeta]

I extracted the subtitles with
gMKVExtractGUI
and, when I open the file I see

WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:0

00:00:00.000 --> 00:00:01.840
So at the end of the last video,

00:00:01.840 --> 00:00:04.810
we left off with a fairly obvious problem here,

I think the problem with ffmpeg arises because of this 2nd line bullshit whatever the **** it is

X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:0

ffmpeg actually extracts the subtitle but it only gives a 7 bytes file with
WEBVTT
as content.
So, it stops at the 2nd line I assume because it doesn't expect a bullshit thing like this

X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:0

What do I do now? I want to find a way to batch extract these subtitles cause there are more files.
I used to do this with powershell command and ffmpeg...

Eh, okay, gMKVExtractGUI seems to be able to batch extract...

[jagabo]

Try:

ffmpeg.exe -i a.mkv bla.vtt

Oops, just tried it. Didn't work with MKV. It works with MP4 though.

https://fftrac-bg.ffmpeg.org/ticket/5641?cversion=1&cnum_hist=5

[paso77]

Open mkv in subtitleedit