Re: keeping bitrate during conversion

astrograph GMX wrote:
> hi,
>
> I am trying to convert .mp4 videos to .3gp, it works, but there is a big 
> difference in bitrate between the original and the converted copy:
>
> ffmpeg -i media/470222.mp4 test3.3gp
> ffmpeg version 0.4.9-pre1, build 4718, Copyright (c) 2000-2004 Fabrice 
> Bellard
>   built on Feb 28 2005 14:45:40, gcc: 3.2.3 20030502 (Red Hat Linux 
> 3.2.3-49)

This is very old. Please upgrade to CVS.

> Input #0, mov,mp4,m4a,3gp, from 'media/470222.mp4':
>   Duration: 00:00:30.0, bitrate: 80 kb/s
>   Stream #0.0: Video: mpeg4, 176x144, 12.00 fps
>   Stream #0.1: Audio: amr_nb, 8000 Hz, mono
> Output #0, 3gp, to 'test3.3gp':
>   Stream #0.0: Video: h263, 176x144, 12.00 fps, q=2-31, 200 kb/s

Normal, 200kb/s is the default bitrate for the ffmpeg command line app.

>   Stream #0.1: Audio: amr_nb, 8000 Hz, mono, 64 kb/s
> Stream mapping:
>   Stream #0.0 -> #0.0
>   Stream #0.1 -> #0.1
> Press [q] to stop encoding
> [h263 @ 0x443014]warning, cliping 1 dct coefficents to -127..127
> ...<snip/>...
> [h263 @ 0x443014]warning, cliping 1 dct coefficents to -127..127
> frame=  360 q=2.0 Lsize=     846kB time=30.0 bitrate= 231.0kbits/s
> video:789kB audio:47kB global headers:0kB muxing overhead 1.184066%
>
> of course I can set the bitrate parameters manually:
>
> ffmpeg -i media/470222.mp4 -b 50 -ab 10 test4.3gp
> ffmpeg version 0.4.9-pre1, build 4718, Copyright (c) 2000-2004 Fabrice 
> Bellard
>   built on Feb 28 2005 14:45:40, gcc: 3.2.3 20030502 (Red Hat Linux 
> 3.2.3-49)
> Input #0, mov,mp4,m4a,3gp, from 'media/470222.mp4':
>   Duration: 00:00:30.0, bitrate: 80 kb/s
>   Stream #0.0: Video: mpeg4, 176x144, 12.00 fps
>   Stream #0.1: Audio: amr_nb, 8000 Hz, mono
> Output #0, 3gp, to 'test4.3gp':
>   Stream #0.0: Video: h263, 176x144, 12.00 fps, q=2-31, 50 kb/s
>   Stream #0.1: Audio: amr_nb, 8000 Hz, mono, 10 kb/s
> Stream mapping:
>   Stream #0.0 -> #0.0
>   Stream #0.1 -> #0.1
> Press [q] to stop encoding
> [h263 @ 0x351014]warning, cliping 1 dct coefficents to -127..127
> [h263 @ 0x351014]warning, cliping 1 dct coefficents to -127..127
> frame=  360 q=4.4 Lsize=     324kB time=30.0 bitrate=  88.6kbits/s
> video:275kB audio:40kB global headers:0kB muxing overhead 3.161163%
>
> question 1: is there a way to tell ffmpeg to keep the (overall) bitrate 
> from the original?

No.

> question 2: is there a command which returns the bitrate(s) for a 
> specific file?

No.

> thx
>
> Phil
>
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