[FFmpeg-user] overlay w/librtmp

[Tom Evans]

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