[FFmpeg-user] Decklink with ffmpeg audio desync

Marton Balint cus at passwd.hu
Sat May 14 02:44:34 CEST 2016

On Fri, 13 May 2016, Dpto. Datos Television Costa Blanca wrote:

> El 12/05/2016 a las 21:19, Marton Balint escribió:
>>> The actual command is:
>>> ./ffmpeg -re -f decklink -i "DeckLink SDI 4K at 2" -c:v mpeg2video -pix_fmt
>>> yuv420p -aspect 16:9 -deinterlace -sc_threshold 1000000000 -b:v 3.5M
>>> -minrate:v 3.5M -maxrate:v 3.5M -bufsize:v 2.4M -acodec mp2 -ac 2 -b:a
>>> 128k-metadata service_name="TVT" -mpegts_service_id 123 -f mpegts
>>> udp://
>>> Just for info, the SDI input comes from a matrix that when switch betwen
>>> sources have a little delay and ffmpeg return a NO INPUT SIGNAL DETECTED 
> ->
>>> Can the desync come from here?
>> Yes, it is possible. Also I noticed you are using -re, there is no need
>> for it, you cannot read from the device faster than realtime.
> I've removed -re from the command, but if that doesnt help, how can I 
> fix the desync? I have no way of "not having" the NO INPUT SIGNAL -> 
> Also, when the signal interrupts I see in the stream the colour bars. Do 
> they come from ffmpeg or from the decklink card?

Bars are coming from ffmpeg, when no input is detected. Apparently 
your inputs are not synchornized... Can you try to feed synchronized 
signal to ffmpeg to rule out this, as a probable source of A-V desync?


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