[FFmpeg-user] Transcoding FLV with no/broken audio

[Lou]

On Thu, 10 Nov 2011 00:00:58 +0000 (UTC)
Jon Drukman <jsd at cluttered.com> wrote:

> I'm using Red5 (open source Flash Media Server) to record videos from
> webcams. Sometimes the files come through with no audio.  I want to
> transcode these files to H.264/AAC, but if there's no audio, I'd like
> to just leave it out.
> 
> I can identify these bad input files by looking at ffmpeg's output:
> 
> Input #0, flv, from 'webcam.flv':
>   Metadata:
>     audiocodecid    : -1
>     duration        : 5
>     videocodecid    : 2
>     canSeekToEnd    : true
>   Duration: 00:00:04.55, start: 0.000000, bitrate: N/A
>     Stream #0.0: Video: flv, yuv420p, 320x240, 1k tbr, 1k tbn, 1k tbc
>     Stream #0.1: Audio: [0][0][0][0] / 0x0000, 0 channels
> 
> No problem.  Audio [0][0][0][0] means no audio.  But how do I specify
> that I don't want any audio in the output? My normal command line is:
> 
> ffmpeg -v 0 -y -i webcam.flv -s 320x240 -acodec libfaac -ab 64k -ac 2
> -ar 44100 -vcodec libx264 -preset fast -b 300k -bt 300k -threads 0
> -vsync 0 -async 1 webcam.flv.mp4
> 
> This fails with:
> 
> Decoder (codec id 0) not found for input stream #0.1
> 
> I tried leaving off all the -acodec, -ab, -ac, -ar options.  This
> fails with:
> 
> [libfaac @ 0x7fa28c01b600] encoding 0 channel(s) is not allowed
> Error while opening encoder for output stream #0.1 - maybe incorrect
> parameters such as bit_rate, rate, width or height
> 
> I tried -acodec copy
> 
> [mp4 @ 0x7fe5fb818c00] sample rate not set
> Could not write header for output file #0 (incorrect codec
> parameters ?)
> 
> I tried -acodec null, -acodec none... That just gives me "unknown
> encoder".
> 
> Any ideas how I can tell it to just ignore the audio entirely?

Try the -an option.