user22306: I am encoding a video with ffmpeg into H.264 stored in an FLV container. I would like to be able to trim segments of this video out as it is still encoding. The video contains no audio.
I am encoding the video like so:
ffmpeg -i recording.mp4 -c libx264 output.flv

And I'm attempting to trim the video with:
ffmpeg -i output.flv -ss 00:00:00.000 -t 00:00:01.000 -c copy output2.mp4

While the video is still encoding, I see this error when I try to trim:
Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)

Also while encoding, using ffprobe, I get information like the following:
Duration: 00:00:26.96, start: 0.080000, bitrate: 126 kb/s
  Stream #0:0: Video: h264 (High), yuv420p, 640x480, 25 fps, 25 tbr, 1k tbn, 50 tbc

How can I go about trimming this file while it's still encoding? I am willing to change container formats from flv to something else if needed. Ultimately, I need to be in mp4, but I don't mind doing some container shuffling to allow me to trim out portions while still encoding. 

user1871: Keep FLV but trim using demuxer seek and duration.
ffmpeg -ss 00:00:03.000 -t 00:00:01.000 -i output.flv -c copy output2.mp4

Also, skip -ss if it's 0 i.e. stream start.

22306: <p>I am encoding a video with ffmpeg into H.264 stored in an FLV container. I would like to be able to trim segments of this video out as it is still encoding. The video contains no audio.</p>

<p>I am encoding the video like so:</p>

<pre><code>ffmpeg -i recording.mp4 -c libx264 output.flv
</code></pre>

<p>And I'm attempting to trim the video with:</p>

<pre><code>ffmpeg -i output.flv -ss 00:00:00.000 -t 00:00:01.000 -c copy output2.mp4
</code></pre>

<p>While the video is still encoding, I see this error when I try to trim:</p>

<pre><code>Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)
</code></pre>

<p>Also while encoding, using ffprobe, I get information like the following:</p>

<pre><code>Duration: 00:00:26.96, start: 0.080000, bitrate: 126 kb/s
  Stream #0:0: Video: h264 (High), yuv420p, 640x480, 25 fps, 25 tbr, 1k tbn, 50 tbc
</code></pre>

<p>How can I go about trimming this file while it's still encoding? I am willing to change container formats from flv to something else if needed. Ultimately, I need to be in mp4, but I don't mind doing some container shuffling to allow me to trim out portions while still encoding. </p>
 1871: <p>Keep FLV but trim using demuxer seek and duration.</p>

<pre><code>ffmpeg -ss 00:00:03.000 -t 00:00:01.000 -i output.flv -c copy output2.mp4
</code></pre>

<p>Also, skip <code>-ss</code> if it's <code>0</code> i.e. stream start.</p>
