Thanks for reporting your issue. Please make sure these boxes are checked before submitting your issue - thank you!

- [x] I looked for a similar issue and couldn't find any.
- [x] I tried with the latest version of GPAC. Installers available at https://gpac.io/downloads/gpac-nightly-builds/
- [x] I give enough information for contributors to reproduce my issue (meaningful title, github labels, platform and compiler, command-line ...).

Detailed guidelines: https://gpac.io/bug-reporting/

I want to push a subtitles track into GPAC in live mode to generate a live HLS/DASH stream. Currently, the subtitles are pushed via a TCP socket from another application (see below).

The GPAC command is:

```bash
gpac \
  -i tcp://0.0.0.0:9091:gpac:tsprobe=false:listen=true txtin  \
  -o res/live.mpd:dual:cmaf=cmf2:segdur=2:rawsub=true:dmode=dynamic -graph
```

From the command I expect GPAC to start creating the playlist and segments live while the VTT text arrives from the socket. What I see is that there are no files created in the `res` folder. And, when I stop the Python client (and the socket is closed), GPAC starts creating the playlist and segments as I expect them to be.

A given segment `0.0.0_dash1.vtt` looks like

```
WEBVTT

00:00.000 --> 00:01.000
Current time: 00:00.000

00:01.000 --> 00:02.000
Current time: 00:01.000
```

Am I missing something from the TCP connection to signal the `dasher` to produce the subtitles track live?

## Python client

This is the code for the `subtitles_client.py` client.

To run it:

```bash
python3 subtitles_client.py
```

which creates the WebVTT track, pushes it to the TCP socket, and prints the pushed string:

```
WEBVTT

00:00.000 --> 00:01.000
Current time: 00:00.000

00:01.000 --> 00:02.000
Current time: 00:01.000

00:02.000 --> 00:03.000
Current time: 00:02.000

00:03.000 --> 00:04.000
Current time: 00:03.000

00:04.000 --> 00:05.000
Current time: 00:04.000

00:05.000 --> 00:06.000
Current time: 00:05.000

00:06.000 --> 00:07.000
Current time: 00:06.000

00:07.000 --> 00:08.000
Current time: 00:07.000
```

```python3
import socket
import threading
import time

def div_remainder(val, div):
    
    return int(val // div), int(val % div)
    
def time_format(milliseconds):
    
    s, ms = div_remainder(milliseconds, 1000)
    m, s = div_remainder(s, 60)
    h, m = div_remainder(m, 60)
    
    if h == 0:
        return '{0:02d}:{1:02d}.{2:03d}'.format(m, s, ms)
    else:
        return '{0:02d}:{1:02d}:{2:02d}.{3:03d}'.format(h, m, s, ms)

def subtitles_thread():
    print("subtitles_thread started")
    
    conn = socket.create_connection(('localhost', 9091))
    
    header = "WEBVTT\n\n"
    conn.send(bytes(header, "utf-8"))
    print(header, end='')
    
    template = "{0} --> {1}\n{2}\n\n"
    
    counter_ms = 0
    delta_ms = 1000
    while True:
        
        curr_time = time_format(counter_ms)
        next_time = time_format(counter_ms + delta_ms)
        msg = 'Current time: {0}'.format(curr_time)
        
        s = template.format(curr_time, next_time, msg)
        conn.send(bytes(s, 'utf-8'))
        print(s, end='')
        
        counter_ms += delta_ms
        time.sleep(delta_ms / 1000.0)
    
    conn.close()
    
    print("subtitles_thread finished")


if __name__ == '__main__':
    
    t1 = threading.Thread(target=subtitles_thread)

    print('STARTING')
    t1.start()

    print('JOINING')
    t1.join()
```

Consume WebVTT live from a TCP socket
This is a GitHub Issue
repo:gpac
owner:gpac
Title : Consume WebVTT live from a TCP socket
Issue date:

--- start body ---
Thanks for reporting your issue. Please make sure these boxes are checked before submitting your issue - thank you!

- [x] I looked for a similar issue and couldn't find any.
- [x] I tried with the latest version of GPAC. Installers available at https://gpac.io/downloads/gpac-nightly-builds/
- [x] I give enough information for contributors to reproduce my issue (meaningful title, github labels, platform and compiler, command-line ...).

Detailed guidelines: https://gpac.io/bug-reporting/

I want to push a subtitles track into GPAC in live mode to generate a live HLS/DASH stream. Currently, the subtitles are pushed via a TCP socket from another application (see below).

The GPAC command is:

```bash
gpac \
  -i tcp://0.0.0.0:9091:gpac:tsprobe=false:listen=true txtin  \
  -o res/live.mpd:dual:cmaf=cmf2:segdur=2:rawsub=true:dmode=dynamic -graph
```

From the command I expect GPAC to start creating the playlist and segments live while the VTT text arrives from the socket. What I see is that there are no files created in the `res` folder. And, when I stop the Python client (and the socket is closed), GPAC starts creating the playlist and segments as I expect them to be.

A given segment `0.0.0_dash1.vtt` looks like

```
WEBVTT

00:00.000 --> 00:01.000
Current time: 00:00.000

00:01.000 --> 00:02.000
Current time: 00:01.000
```

Am I missing something from the TCP connection to signal the `dasher` to produce the subtitles track live?

## Python client

This is the code for the `subtitles_client.py` client.

To run it:

```bash
python3 subtitles_client.py
```

which creates the WebVTT track, pushes it to the TCP socket, and prints the pushed string:

```
WEBVTT

00:00.000 --> 00:01.000
Current time: 00:00.000

00:01.000 --> 00:02.000
Current time: 00:01.000

00:02.000 --> 00:03.000
Current time: 00:02.000

00:03.000 --> 00:04.000
Current time: 00:03.000

00:04.000 --> 00:05.000
Current time: 00:04.000

00:05.000 --> 00:06.000
Current time: 00:05.000

00:06.000 --> 00:07.000
Current time: 00:06.000

00:07.000 --> 00:08.000
Current time: 00:07.000
```

```python3
import socket
import threading
import time

def div_remainder(val, div):
    
    return int(val // div), int(val % div)
    
def time_format(milliseconds):
    
    s, ms = div_remainder(milliseconds, 1000)
    m, s = div_remainder(s, 60)
    h, m = div_remainder(m, 60)
    
    if h == 0:
        return '{0:02d}:{1:02d}.{2:03d}'.format(m, s, ms)
    else:
        return '{0:02d}:{1:02d}:{2:02d}.{3:03d}'.format(h, m, s, ms)

def subtitles_thread():
    print("subtitles_thread started")
    
    conn = socket.create_connection(('localhost', 9091))
    
    header = "WEBVTT\n\n"
    conn.send(bytes(header, "utf-8"))
    print(header, end='')
    
    template = "{0} --> {1}\n{2}\n\n"
    
    counter_ms = 0
    delta_ms = 1000
    while True:
        
        curr_time = time_format(counter_ms)
        next_time = time_format(counter_ms + delta_ms)
        msg = 'Current time: {0}'.format(curr_time)
        
        s = template.format(curr_time, next_time, msg)
        conn.send(bytes(s, 'utf-8'))
        print(s, end='')
        
        counter_ms += delta_ms
        time.sleep(delta_ms / 1000.0)
    
    conn.close()
    
    print("subtitles_thread finished")


if __name__ == '__main__':
    
    t1 = threading.Thread(target=subtitles_thread)

    print('STARTING')
    t1.start()

    print('JOINING')
    t1.join()
```

--- end body ---

None