[FFmpeg-user] audio-only flv over rtmp

Leo Currie leo.currie at gmail.com
Mon Aug 5 21:23:13 CEST 2013

On 5 August 2013 11:50, Christian Ebert <blacktrash at gmx.net> wrote:

> * Leo Currie on Monday, August 05, 2013 at 11:30:52 +0100
> > I'm trying to generate an RTMP live stream for Flash clients that
> contains
> > audio only.
> Why don't you stream just MP3?

My source is actually a 32kbps AAC+ stream coming from an Icecast server,
so I should really be doing '-acodec copy'.

> > Is there a special option to prevent the flv muxer generating a video
> > stream?
> >
> > Here's an example of the kind of stream I'd like to generate:
> > rtmp://
> >
> > I'm trying this:
> > ffmpeg -re -i (my input stream) -acodec aac -strict experimental -ab 96k
> > -ar 44100 -vn -f flv rtmp://
> > ..which connects to my local nginx instance running the rtmp module.
> >
> > When I try to play the stream in VLC, it complains about an 'undf' video
> > format, but audio plays fine. Looking at the stream properties in VLC I
> can
> > see there is indeed an 'undf' video stream 0, with the audio being
> stream 1.
> >
> > Is there an option for the flv muxer to prevent this video stream being
> > generated? I tried -vn but this doesn't do what I expect.
> >
> > Or am I going about this the wrong way?
> FLV is Flash Video, so a missing video track does not make sense
> imho. Furthermore I don't think you need this contortion for RTMP
> (see above). I packed audio into a FLV container for
> *pseudo*streaming, but again then you need a _minimal_ video
> track to be able to inject metadata.

Indeed, and MPEG is Moving Picture Experts Group, but we can have MP3
audio. So perhaps none of these formats have very good names!

I didn't know that a video track was needed for metadata, so perhaps all I
need to do is be able to generate the "right kind" of dummy video track for
my FLV.

Or is there another way to stream aac audio over rtmp in a way that Flash
player (e.g. JWPlayer) will understand?
Perhaps a different mux? Is this what you meant by streaming in MP3 - can I
stream without a container?

Thanks -


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