[FFmpeg-user] Why does this half the filesize

[belcampo]

On 05/05/11 21:54, Cecil Westerhof wrote:
> When executing:
>      ffmpeg -y -sameq -i original/resolutie.avi resolutie.avi
>
> The resulting file is half as big as the original one. Why is this?
>
> The reason I do this, is that I capture something from XWindows and I
> have to cut the last few seconds.
>
> If it is useful:
> ffmpeg -i original/resolutie.avi
> FFmpeg version SVN-r201104161305, Copyright (c) 2000-2011 the FFmpeg developers
>    built on Apr 16 2011 11:36:21 with gcc 4.5.1 20101208 [gcc-4_5-branch revision 167585]
>    configuration: --shlibdir=/usr/lib --prefix=/usr --mandir=/usr/share/man --libdir=/usr/lib --enable-shared --enable-libmp3lame --enable-libvorbis --enable-libtheora --enable-libspeex --enable-libxvid --enable-postproc --enable-gpl --enable-x11grab --extra-cflags='-fomit-frame-pointer -fmessage-length=0 -O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector -funwind-tables -fasynchronous-unwind-tables -g -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -I/usr/include/gsm' --enable-debug --disable-stripping --enable-libgsm --enable-libschroedinger --enable-libdirac --enable-avfilter --enable-libvpx --enable-version3 --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libx264 --enable-libdc1394 --enable-pthreads --enable-librtmp
>    libavutil    50. 40. 1 / 50. 40. 1
>    libavcodec   52.119. 1 / 52.119. 1
>    libavformat  52.108. 0 / 52.108. 0
>    libavdevice  52.  4. 0 / 52.  4. 0
>    libavfilter   1. 79. 0 /  1. 79. 0
>    libswscale    0. 13. 0 /  0. 13. 0
>    libpostproc  51.  2. 0 / 51.  2. 0
> Input #0, avi, from 'original/resolutie.avi':
>    Metadata:
>      encoder         : Lavf52.108.0
>    Duration: 00:00:53.93, start: 0.000000, bitrate: 2809 kb/s
>      Stream #0.0: Video: mpeg4, yuv420p, 1028x795 [PAR 1:1 DAR 1028:795], 15 tbr, 15 tbn, 15 tbc
>      Stream #0.1: Audio: pcm_s16le, 44100 Hz, 2 channels, s16, 1411 kb/s
> At least one output file must be specified
>
>
>
> ffmpeg -i resolutie.avi
> FFmpeg version SVN-r201104161305, Copyright (c) 2000-2011 the FFmpeg developers
>    built on Apr 16 2011 11:36:21 with gcc 4.5.1 20101208 [gcc-4_5-branch revision 167585]
>    configuration: --shlibdir=/usr/lib --prefix=/usr --mandir=/usr/share/man --libdir=/usr/lib --enable-shared --enable-libmp3lame --enable-libvorbis --enable-libtheora --enable-libspeex --enable-libxvid --enable-postproc --enable-gpl --enable-x11grab --extra-cflags='-fomit-frame-pointer -fmessage-length=0 -O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector -funwind-tables -fasynchronous-unwind-tables -g -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -I/usr/include/gsm' --enable-debug --disable-stripping --enable-libgsm --enable-libschroedinger --enable-libdirac --enable-avfilter --enable-libvpx --enable-version3 --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libx264 --enable-libdc1394 --enable-pthreads --enable-librtmp
>    libavutil    50. 40. 1 / 50. 40. 1
>    libavcodec   52.119. 1 / 52.119. 1
>    libavformat  52.108. 0 / 52.108. 0
>    libavdevice  52.  4. 0 / 52.  4. 0
>    libavfilter   1. 79. 0 /  1. 79. 0
>    libswscale    0. 13. 0 /  0. 13. 0
>    libpostproc  51.  2. 0 / 51.  2. 0
> Input #0, avi, from 'resolutie.avi':
>    Metadata:
>      encoder         : Lavf52.108.0
>    Duration: 00:00:53.93, start: 0.000000, bitrate: 1458 kb/s
>      Stream #0.0: Video: mpeg4, yuv420p, 1028x795 [PAR 1:1 DAR 1028:795], 15 tbr, 15 tbn, 15 tbc
>      Stream #0.1: Audio: mp2, 44100 Hz, stereo, s16, 64 kb/s
> At least one output file must be specified
>
"Normally" one specifies what ffmpeg has to do:
ffmpeg -i source.ext -acodec somecodec somecodec-params -vcodec 
somecodec somecodec-params resulting.ext.
Where 'somecodec somecodec-params" in above case should/could be
copy.
Resulting in:
ffmpeg -i source.ext -acodec copy -vcodec copy result.ext
Maybe reading the manuals and/or looking for samples the next time ??