[FFmpeg-user] FFMPEG output to append to a text file without overwriting the content

robertlazarski robertlazarski at gmail.com
Tue Jun 5 03:36:47 EEST 2018

On Mon, Jun 4, 2018 at 6:06 PM, Sana Tafleen <sana.tafleen at gmail.com> wrote:

> Hello,
> I am sending a UDP stream to the destination and saving the contents of the
> FFMPEG output to a text file. I run the ffmpeg command in a loop as
> follows,
> while :
> do
>       echo `ffmpeg -hide_banner -f v4l2 -i /dev/video0 -c:v libx264 -f
> mpegts tcp://ip:port -c:v libx264 /path/to/.mp4 2> out.txt -y`
> done
> When I disconnect the cable connected the destination, the above ffmpeg
> process stops and a new one starts oevrwriting the content of the output
> that has been saved. And when I reconnect the cable, a new ffmpeg process
> starts and its output is what is displayed in the out.txt file.
> I need the output of each ffmpeg process that runs to an output file. Can
> anyone please suggest me a way to do it?

This part of the command, '2> out.txt ' says (a) redirect stderr and not
stdout, to out.txt. And (b) overwrite the previous contents.

You can append instead of overwrite by using '2>> out.txt ' .

I would not expect ffmpeg to create a new process in that loop but I have
no experience with mpegts. I would try -stdin since I have seen unexpected
behavior without it in loops.

A long shot would be using nohup, if its a hangup of some sort. I would try
that if I was still stuck. Then strace on the command to see why it was
creating the extra process.

Kind regards,

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