[FFmpeg-user] Sliding text banner (was: Newbie questions)

[Nicolas George]

Le duodi 2 thermidor, an CCXX, Orbisoft Support a écrit :
> I have just used ffmpeg for the first time today. I have a few questions.

Not a big deal, but in the future, try to choose a subject text that says
what your question is about.

> - I want a horizontal news scroller video going across the bottom of the
> screen
> - So I used ASP.NET VB code to create one wide bitmap image (25000 x 30
> pixels)
> - On that image I used ASP.NET .DrawString to draw text (Arial 18 Bold)
> based on one large text string which contained news item text from a RSS
> - From that I extracted and saved 25000 png images, all 1920 x 30 pixels
> but each starting at point x from the original image where x=x+1

Technically, you can only do extract 25000-1920+1 = 23081 PNG like that.

> 1) What is the maximum frame rate I can use? Currently although it is
> smooth, it takes about 33 seconds to go from right to left since it is only
> moving at one pixel at a time. I want it to take about 12 seconds

With MPEG like you did, not much. With other codecs and containers, you can
go to ridiculously high frame rates. But that is just wasting CPU: just draw
the text or extract the part of the text at the rate you need.

> 2) Should I use PNG format images or choose something else (ASP.NET lets me
> choose the image format to Save As)?

PNG seems very fine for that.

But you do not have to do that at all, you can do everything in ffmpeg,
using the drawtext filter:

./ffmpeg_g -i video -vf "drawtext=fontfile=LinLibertine_R.otf:\
text=You should not be watching this:fontsize=40:\
fontcolor=white:shadowcolor=black:shadowx=1:shadowy=1:\
x=W*(1-0.2*t):y=H+descent-ascent' output

The coefficient before t in the x expression controls the speed.

> 3) I want to embed the movie on a webpage. What then is the best video
> format for that?

This is a difficult question.

> 4) Are there any other things I should do to optimize the quality,
> smoothness and file size? Currently the movie is 92 MB.

It depends completely on the answer to question 3.

Regards,

-- 
  Nicolas George
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