[FFmpeg-user] what does start mean in ffmpeg output

[Etienne Buira]

On Thu, May 26, 2011 at 12:29:34PM +0200, Feurstein, Michael wrote:
> Hi,
> 
> I'm in the process of doing live streaming with ffmpeg and VLC. My biggest challenge right now is getting audio and video in sync.
> In my setup I am muxing a live udp stream from VLC with a live MP3 stream from Nicecast (environment: Mac OS X), restreaming it ffmpeg in order to sync it with VLC and stream it again (I know... kinda complicated but it works). I noticed the following output from ffmpeg, where start is always slightly different - I am assuming it has sth todo with the beginning of the udp stream.
> 
> Input #0, mpegts, from, 'udp://224.0.0.1.1234':
>                 Duration: N/A, start: 2597.648522, bitrate: N/A
> 
> When syncing the muxed stream with this output I need to delay audio by 8 seconds in VLC (--audio-desync=8000)
> 
> Now my question is what does the start stand for officially - milliseconds, delay...??
> Google only found me this (http://web.archiveorange.com/archive/v/KKJCyjygu3YKlis65Nfq) which apparently can't be up to date otherwise this would mean 2000 seconds timestamp
> 
> Can anyone explain this to me?
> 
> Thanks a lot!
> 
> Greetings

Hi.

start is in seconds.

The reason is that every frame needs to have a timestamp, to know when
to decode and when to display it. On continuous streams, there is no
other option than increase those values continuously.
So, by example, if you dump your broadcast to a file, and try to seek '10
seconds after the beginning of the file', it will try to find timestamps
matching 2607.648522 seconds.