[FFmpeg-user] overlay w/librtmp

Scott Freeman scottf at tvw.org
Mon Mar 26 19:19:06 CEST 2012

Tom, thanks for the clarification. Like I mentioned, I thought it would be
a stretch to call it a bug. And you confirmed my guess on how
"copy" worked, thank you.

I am curious though about what you said and this may be a topic for another
thread. Why couldn't ffmpeg be able to detect the input video information
and create a "similar" output string to essentially copy the inputs
settings? I could surely do that or something similar with a script and
some program logic to generate a output string before starting the encode.
I think it would make for a good feature built-in, especially when users
sometimes are just re-encoding a video to do effects and overlays and such.
Am I way off here?

Thanks again Tom, for taking the time to reply to my post.


On Mon, Mar 26, 2012 at 7:54 AM, Tom Evans <tevans.uk at googlemail.com> wrote:

> On Mon, Mar 26, 2012 at 3:34 PM, Scott Freeman <scottf at tvw.org> wrote:
> > Thanks for the reply, I figured out what was going on (running 0.10).
> > Evidently you cannot use the "-acodec copy -vcodec copy" for the codec
> > setting from the source media for your output. The overlay filter will
> > throw no errors, but will not work. You have to specify the output codec
> > parameters (even if they are the same as the inputs) to get the overlay
> to
> > work.
> > I would stretch to call this a bug or an oversight but I think I
> understand
> > the workflow and the logic there being a programmer.
> > It does work now. I hope that this could though be at least documented or
> > updated in the next revision.
> >
> >
> It's definitely not a bug - how can ffmpeg render a logo on the output
> video when you tell it to copy the video data?
> "-vcodec copy" literally means "copy, byte for byte, the data in the
> video stream", it definitely does not mean "re-encode the video using
> the same parameters it was originally encoded with" (for a start, most
> of the parameters that it was encoded with cannot even be known at
> that point!)
> Cheers
> Tom
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