On Sat, 9 May 2020, Martin wrote:
Hi!
Anybody have an idea why I get a couple of seconds of latency when
outputting to a decklink device? I
ffmpeg -fflags nobuffer -i srt://x -f decklink -pix_fmt uyvy422 -c:a
pcm_s16le -ar 48000 -ac 2 "UltraStudio SDI"
Input is a TS stream SRT or UDP, input type does not r matter. Im getting
almost 4 seconds of delay on the SDI output compared to the stream. Seems a
bit high? One would expect a couple of frames. I have seen this question on
a few places but never seen an answer or solution.
Decklink driver 10.11.4, Windows
I only see this behaviour in ffmpeg not in other programs that uses
decklink output, Premiere, OBS etc.
Latency comes from multiple sources:
1) The most significant is probably input probing. You can limit this with
-probesize and -analyzeduration.
2) decklink preroll - you can set this with -preroll, but a very low value
will cause choppy output.
3) other buffering - I am sure there are other places :)
By setting 1) and 2) you can probably can reduce the latency, but I'd
think it will still be higher than special purpose software.
Regards,
Marton
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