[FFmpeg-devel] first experience with ffmpeg

[Stefano Sabatini]

On date Friday 2008-02-15 02:09:19 -0500, D. Hugh Redelmeier encoded:
> As a developer, I value learning about users first exposure to a
> program.  Newbies trip over things that the experienced no longer
> notice.  That is why I am trying to describe my initial experiences
> with ffmpeg even if they will turn out to be embarrassing.
> 
> This is going to be presented as a narrative.  Large parts may be
> uninteresting.  I will highlight points that I hope are worth noting
> with "===>".
[...] 

> My first (recorded) use of ffmpeg:
> 
>     $ ffmpeg -v -i 2008.02.11-19.28.wma 2008.02.11-19.28.mp3
>     FFmpeg version SVN-r8876, Copyright (c) 2000-2007 Fabrice Bellard, et al.
>       configuration: --prefix=/usr --incdir=/usr/include/ffmpeg --libdir=/usr/lib64 --shlibdir=/usr/lib64 --mandir=/usr/share/man!
>       libavutil version: 49.4.0
>       libavcodec version: 51.40.4
>       libavformat version: 51.12.1
>       built on May  3 2007 12:41:19, gcc: 4.1.2 20070424 (Red Hat 4.1.2-11)
>     File '2008.02.11-19.28.wma' already exists. Overwrite ? [y/N] n
>     Not overwriting - exiting
> 
> The problem is that -v takes an argument, so it "ate" the -i, leaving
> what I thought of as in input file to be treated as an output file.
> Thank goodness for the overwrite warning!
> 
> ===> the ffmpeg program should diagnose malformed arguments to -v.
> 
> I more carefully read the manual and tried "-v verbose" which made
> ffmpeg quiet -- pretty counterintuitive!

This happens everytime we use atoi() in ffmpeg.c. When the string is
unparsable as a string ffmpeg uses the value 0 without to warn the
user a blink.
 
What about the attached patch (I think there could be some trouble
from the conversion from long int to int)?

Suggested log: replace atoi() in ffmpeg.c with the parse_int_or_die()
function.

> ===> the ffmpeg manpage's description of the -v flag should explain
>      that "verbose" is not a literal string but (I imagine) an integer.
>      It should explain what possible values are.

Agree.
 
> Eventually, I converted the file to .mp3.
> 
> 
> I had captured an hour of radio.  I wanted to extract a few minutes
> from it.  I played the mp3 with xmms and wrote down the start time and
> duration of the part I wished to capture.
> 
> I then used this the do the extraction
> 
>     $ ffmpeg -ss 00:23:44 -t 00:09:15 -i 2008.02.11-19.28.wma don.mp3
> 
> This did not work.  It seemed as if ffmpeg ignored the -ss and just
> started extracting from the beginning.  I don't know why.  Perhaps you
> can tell me from the verbose output.
> 
>     $ ffmpeg -v 9 -ss 00:23:44 -t 00:09:15 -i 2008.02.11-19.28.wma don.mp3
>     FFmpeg version SVN-r8876, Copyright (c) 2000-2007 Fabrice Bellard, et al.
                     ^^^^^^^^^
>       configuration: --prefix=/usr --incdir=/usr/include/ffmpeg --libdir=/usr/lib64 --shlibdir=/usr/lib64 --mandir=/usr/share/man --arch=x86_64 --extra-cflags=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic --enable-libmp3lame --enable-libogg --enable-libtheora --enable-libvorbis --enable-libfaad --enable-libfaac --enable-libgsm --enable-xvid --enable-x264 --enable-liba52 --enable-liba52bin --enable-libdts --enable-pp --enable-pthreads --disable-static --enable-shared --enable-gpl --disable-debug --disable-opts --disable-strip
>       libavutil version: 49.4.0
>       libavcodec version: 51.40.4
>       libavformat version: 51.12.1
>       built on May  3 2007 12:41:19, gcc: 4.1.2 20070424 (Red Hat 4.1.2-11)

Really ancient version acccording to the ffmpeg standards. Retry with
the newest and greatest, maybe that has been fixed.

Regards.
-- 
Stefano Sabatini
Linux user number 337176 (see http://counter.li.org)
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