[FFmpeg-user] Null processed Video file is not the same as original

MohammadH Sedaaghi sedaaghi at yahoo.com
Thu Nov 1 06:57:12 CET 2012

Dear Carl
I tested your suggestion but as expected, it did’t work. The
parameter –r 25 is not important.
I need to do video processing. For this purpose, I want
first to do null processing. It means that I want to read frame info of a video
file (e.g., orig.mp4) into still images and a
wave file. Then merge them into another video file (say it output.mp4). I expect both files (orig.mp4 and output.mp4)
be the same but they are not and output.mp4 has more frames than orig.mp4. That
is my question. To illustrate the problem, I make three following stages (the
size of orig.mp4 is 284 KB):
Stage 1: Read orig.mp4 into
still images+wav file:
del *.jpg
del *.wav
ffmpeg -i orig.mp4 -r 25 Img%d.jpg
It generates 51 .jpg images (Img1.jpg, Img2.jpg, etc.) and 1 .wav file is
Stage 2: still images+wav file
into output.mp4:
ffmpeg -i Wave.wav -f image2 -i
Img%d.jpg -r 25 output.mp4
It produces output.mp4 with a size of 328 KB!, meaning that
it differs from orig.mp4. Why? 
To show how it differs, I make the following stage:
Stage 3: Read output.mp4 into
still images+wav file:
del *.jpg
del *.wav
ffmpeg -i output.mp4 -r 25 PImg%d.jpg
it produces 52 .jpg images and 1 bigger .wav file compared
to the first .wav file. Even the information inside images differ (i.e.,
Img1.jpg differs from PImg1.jpg)
I should be confident about null processing at first to be
able to add some processing later.
Could you please give me a hint about why the number of
files should and therefore their contents should be different in every try?
Thanks in advance.

From: Carl Eugen Hoyos <cehoyos at ag.or.at>

To: ffmpeg-user at ffmpeg.org 
Sent: Wednesday, October 31, 2012 7:34 PM
Subject: Re: [FFmpeg-user] -r default value
MohammadH Sedaaghi <sedaaghi <at> yahoo.com> writes:

> 30 .jpg images and 1 .wav file is generated.
> To test the correctness of ffmpeg if in turn we run 
> the following command:

> ffmpeg -i Wave.wav -f image2 -i Img%d.jpg -r 30 out.mp4

If you had added complete, uncut console output, you could 
see that ffmpeg defaults to "-r 25" for the input since 
you did not provide another value.

Please always use a valid subject when mailing.

Carl Eugen

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