[Red5] transcoding flv to mp3

[Art Clarke]

my bet is your source FLV file has 8khz nellymoser audio in it, but the
ffmpeg is mistakenly thinking it's 5.5khz.  I've heard of potential problems
with the flv files with either FFMPEG or  Red5 (I think ffmpeg but I haven't
tried to track it down) when using 8khz nellymoser.

To work around, save your files either as 5.5 or 11khz nellymoser.  FLV has
a special header value for 8khz nellymoser audio that not all other software
correctly respects.

- Art

On Wed, Mar 11, 2009 at 1:42 PM, Robbie Clutton <robert.clutton at gmail.com>wrote:

> Hi,
>
> I'm trying to transcode the flv files into mp3 using ffmpeg, but am
> having issues with the speed of the transcoded mp3 files (i.e. the
> speech is much slower).  You can see from the output below that the
> audio sampling rate is 5512 hz, using nellymoser and has a mono
> channel.  It seems regardless of the options set (using -ar and -ab)
> the output is the same.  Has anyone done this, or have come across
> this issue before?  I've built ffmpeg with libmp3lame enabled, and
> have tried outputting to mp3 and wav.
>
> Cheers
>
> Robbie
>
> FFmpeg version SVN-r17943, Copyright (c) 2000-2009 Fabrice Bellard, et al.
>  configuration: --enable-libmp3lame
>  libavutil     50. 0. 0 / 50. 0. 0
>  libavcodec    52.21. 0 / 52.21. 0
>  libavformat   52.31. 1 / 52.31. 1
>  libavdevice   52. 1. 0 / 52. 1. 0
>  libswscale     0. 7. 1 /  0. 7. 1
>  built on Mar 11 2009 19:50:21, gcc: 4.1.3 20070929 (prerelease)
> (Ubuntu 4.1.2-16ubuntu2)
> [flv @ 0xe66a60]Could not find codec parameters (Video: 0x0000)
> Input #0, flv, from '/root/welcome.flv':
>  Duration: 00:00:28.09, start: 0.000000, bitrate: N/A
>    Stream #0.0: Video: 0x0000, 1k tbr, 1k tbn, 1k tbc
>    Stream #0.1: Audio: nellymoser, 5512 Hz, mono, s16
> File '/root/welcome.wav' already exists. Overwrite ? [y/N] y
> Output #0, wav, to '/root/welcome.wav':
>    Stream #0.0: Audio: pcm_s16le, 5512 Hz, mono, s16, 88 kb/s
> Stream mapping:
>  Stream #0.1 -> #0.0
> Press [q] to stop encoding
> size=     439kB time=40.73 bitrate=  88.2kbits/s
> video:0kB audio:438kB global headers:0kB muxing overhead 0.009799%
>
>
>
> FFmpeg version SVN-r17943, Copyright (c) 2000-2009 Fabrice Bellard, et al.
>  configuration: --enable-libmp3lame
>  libavutil     50. 0. 0 / 50. 0. 0
>  libavcodec    52.21. 0 / 52.21. 0
>  libavformat   52.31. 1 / 52.31. 1
>  libavdevice   52. 1. 0 / 52. 1. 0
>  libswscale     0. 7. 1 /  0. 7. 1
>  built on Mar 11 2009 19:50:21, gcc: 4.1.3 20070929 (prerelease)
> (Ubuntu 4.1.2-16ubuntu2)
> [flv @ 0xe66a60]Could not find codec parameters (Video: 0x0000)
> Input #0, flv, from '/root/welcome.flv':
>  Duration: 00:00:28.09, start: 0.000000, bitrate: N/A
>    Stream #0.0: Video: 0x0000, 1k tbr, 1k tbn, 1k tbc
>    Stream #0.1: Audio: nellymoser, 5512 Hz, mono, s16
> File '/root/welcome.mp3' already exists. Overwrite ? [y/N] y
> Output #0, mp3, to '/root/welcome.mp3':
>    Stream #0.0: Audio: libmp3lame, 8000 Hz, mono, s16, 64 kb/s
> Stream mapping:
>  Stream #0.1 -> #0.0
> Press [q] to stop encoding
> size=     320kB time=40.90 bitrate=  64.0kbits/s
> video:0kB audio:320kB global headers:0kB muxing overhead 0.009781%
>
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