Send seek command to running ffmpeg instance

Actually a seek command is kind of documented in the ffmpeg documentation:

Both movie and amovie support the following commands:

• seek Perform seek using "av_seek_frame". The syntax is: seek stream_index|timestamp|flags

  • stream_index: If stream_index is -1, a default stream is selected, and timestamp is automatically converted from AV_TIME_BASE units to the stream specific time_base.
  • timestamp: Timestamp in AVStream.time_base units or, if no stream is specified, in AV_TIME_BASE units.
  • flags: Flags which select direction and seeking mode.

• get_duration Get movie duration in AV_TIME_BASE units.

I have tried running a command like this:

ffmpeg -f lavfi -i 'movie=filename=myvid.mp4' -codec:v libx264 -an -f mpegts - > /dev/null

Then I press c and enter the command all -1 seek 0|3|0, but no matter which combination I try, I get back the same error Command reply for stream 0: ret:-78 res:

I've also tried this command, but it gives the same error when trying to seek:

ffmpeg -i myvid.mp4 -codec:v libx264 -an -f mpegts - > /dev/null

There is very little information about the seek operation on the internet, but I managed to find this: http://ffmpeg.org/pipermail/ffmpeg-devel/2013-September/148070.html

Here he says that:

the "lavfi" demuxer has its own private filtergraph and provides no means (that i know of) to inject command from the outside of this filtergraph into it.

So all this indicates that may or may not be possible to seek on a running ffmpeg instance. At least those who may have succeeded with it have kept how to do it to themselves.