[FFmpeg-devel] make work (live) libsrt

mypopy at gmail.com mypopy at gmail.com
Fri Aug 24 03:38:01 EEST 2018


On Fri, Aug 24, 2018 at 2:55 AM Marton Balint <cus at passwd.hu> wrote:
>
>
>
> On Thu, 23 Aug 2018, mypopy at gmail.com wrote:
>
> > On Wed, Aug 22, 2018 at 4:30 AM Tudor Suciu <tudor.suciu at gmail.com> wrote:
> >>
> >> Hello,
> >>
> >> I get errors when I try to send a live srt stream that the first packet is
> >> too big:
> >> 21:30:39.896626/ffmpeg*E: SRT.c: LiveSmoother: payload size: 1504 exceeds
> >> maximum allowed 1316
> >>
> >> Here are example commands for server and client:
> >> ffmpeg -re -i ~/Downloads/ToS-4k-1920.mov -vcodec libx264 -g 50 -refs 1 -s
> >> 640x360 -b:v 1000k -acodec aac -b:a 64k -flush_packets 0 -f mpegts "srt://
> >> 127.0.0.1:5555?mode=listener"
> >> ffplay srt://127.0.0.1:5555
> >>
> >> A patch that fully solves the issue is:
> >> diff --git a/libavformat/libsrt.c b/libavformat/libsrt.c
> >> index 0f9529d263..156a4776e2 100644
> >> --- a/libavformat/libsrt.c
> >> +++ b/libavformat/libsrt.c
> >> @@ -412,6 +412,8 @@ static int libsrt_open(URLContext *h, const char *uri,
> >> int flags)
> >>          return AVERROR_UNKNOWN;
> >>      }
> >>
> >> +    h->max_packet_size = 1316;
> >> +
> >>      /* SRT options (srt/srt.h) */
> >>      p = strchr(uri, '?');
> >>      if (p) {
> >>
> >> How would you like this option to be made work in a way that can be
> >> accepted in ffmpeg?
> >> Is there a way to change the max packet size without this patch?
> >>
> > In your case, I don't think hard coding max packet size == 1316 is not
> > a good idea in loopback device, and after deep in the srt
> > library(https://github.com/Haivision/srt) source code, I think srt
> > library need to fix the hardcode about packet size limition.
>
> I can't think of a scenario where limiting the packet size actually causes
> problems, but if you insist on not limiting it in general, then the max
> packet size should be settable using an option, same way it is for UDP.
> (pkt_size option). I'd suggest using 1316 as default, because that
> is the more common (and currently the only working) use case...
>
> Thanks,
> Marton
I agree with you, giving an option like pkt_size and using 1316 as the
default in this case is a better way to fix this issue.


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