> On Sep 30, 2021, at 9:14 AM, lance.lmw...@gmail.com wrote:
>
> From: Limin Wang <lance.lmw...@gmail.com>
>
> Signed-off-by: Limin Wang <lance.lmw...@gmail.com>
> ---
> doc/protocols.texi | 10 ++++++++++
> libavformat/libsrt.c | 7 +++++++
> 2 files changed, 17 insertions(+)
>
> diff --git a/doc/protocols.texi b/doc/protocols.texi
> index 726e5f1..9c246f8 100644
> --- a/doc/protocols.texi
> +++ b/doc/protocols.texi
> @@ -1496,6 +1496,16 @@ when the old encryption key is decommissioned. Default
> is -1.
> -1 means auto (0x1000 in srt library). The range for
> this option is integers in the 0 - @code{INT_MAX}.
>
> +@item snddropdelay=@var{microseconds}
> +The sender's delay before dropping packets. This delay is
> +added to the default drop delay time interval value.
> +Keep in mind that the longer the delay, the more probable it
> +becomes that packets would be retransmitted uselessly because
> +they will be dropped by the receiver anyway.
> +
> +Default is -1 means auto which typically means do not drop
> +packets on the sender at all.
There are two issues here:
Firstly, -1 means auto for our libsrt wrapper. "typically means do not drop
packets on the sender at all” is incorrect. The default value of libsrt is
0 for live mode, -1 for file mode. Live mode is the default and the file mode
doesn’t matter much for FFmpeg, TBH.
Secondly, since our wrapper and libsrt defined different sematic for -1, now
it’s impossible to pass -1 to libsrt.
And the description from libsrt doc
> Keep in mind that the longer the delay, the more probable it becomes that
> packets would be
> retransmitted
can mislead the user to set a higher value for it, which is not a good idea.
I don’t know how to improve that.
> +
> @item payload_size=@var{bytes}
> Sets the maximum declared size of a packet transferred
> during the single call to the sending function in Live
> diff --git a/libavformat/libsrt.c b/libavformat/libsrt.c
> index c6308d1..13697d2 100644
> --- a/libavformat/libsrt.c
> +++ b/libavformat/libsrt.c
> @@ -65,6 +65,7 @@ typedef struct SRTContext {
> int enforced_encryption;
> int kmrefreshrate;
> int kmpreannounce;
> + int64_t snddropdelay;
> #endif
> int mss;
> int ffs;
> @@ -111,6 +112,7 @@ static const AVOption libsrt_options[] = {
> { "enforced_encryption", "Enforces that both connection parties have the
> same passphrase set",
> OFFSET(enforced_encryption), AV_OPT_TYPE_BOOL, { .i64 = -1 }, -1, 1,
> .flags = D|E },
> { "kmrefreshrate", "The number of packets to be transmitted after
> which the encryption key is switched to a new key", OFFSET(kmrefreshrate),
> AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, .flags = D|E },
> { "kmpreannounce", "The interval between when a new encryption key
> is sent and when switchover occurs", OFFSET(kmpreannounce),
> AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, .flags = D|E },
> + { "snddropdelay", "The sender's delay(in microseconds) before
> dropping packets", OFFSET(snddropdelay),
> AV_OPT_TYPE_INT64, { .i64 = -1 }, -1, INT64_MAX, .flags = D|E },
> #endif
> { "mss", "The Maximum Segment Size",
> OFFSET(mss), AV_OPT_TYPE_INT, { .i64 = -1
> }, -1, 1500, .flags = D|E },
> { "ffs", "Flight flag size (window size) (in bytes)",
> OFFSET(ffs), AV_OPT_TYPE_INT, { .i64 = -1
> }, -1, INT_MAX, .flags = D|E },
> @@ -318,6 +320,7 @@ static int libsrt_set_options_pre(URLContext *h, int fd)
> int latency = s->latency / 1000;
> int rcvlatency = s->rcvlatency / 1000;
> int peerlatency = s->peerlatency / 1000;
> + int snddropdelay = s->snddropdelay / 1000;
> int connect_timeout = s->connect_timeout;
>
> if ((s->mode == SRT_MODE_RENDEZVOUS && libsrt_setsockopt(h, fd,
> SRTO_RENDEZVOUS, "SRTO_RENDEZVOUS", &yes, sizeof(yes)) < 0) ||
> @@ -334,6 +337,7 @@ static int libsrt_set_options_pre(URLContext *h, int fd)
> #endif
> (s->kmrefreshrate >= 0 && libsrt_setsockopt(h, fd,
> SRTO_KMREFRESHRATE, "SRTO_KMREFRESHRATE", &s->kmrefreshrate,
> sizeof(s->kmrefreshrate)) < 0) ||
> (s->kmpreannounce >= 0 && libsrt_setsockopt(h, fd,
> SRTO_KMPREANNOUNCE, "SRTO_KMPREANNOUNCE", &s->kmpreannounce,
> sizeof(s->kmpreannounce)) < 0) ||
> + (s->snddropdelay >= 0 && libsrt_setsockopt(h, fd,
> SRTO_SNDDROPDELAY, "SRTO_SNDDROPDELAY", &snddropdelay,
> sizeof(snddropdelay)) < 0) ||
> #endif
> (s->mss >= 0 && libsrt_setsockopt(h, fd, SRTO_MSS, "SRTO_MSS",
> &s->mss, sizeof(s->mss)) < 0) ||
> (s->ffs >= 0 && libsrt_setsockopt(h, fd, SRTO_FC, "SRTO_FC", &s->ffs,
> sizeof(s->ffs)) < 0) ||
> @@ -549,6 +553,9 @@ static int libsrt_open(URLContext *h, const char *uri,
> int flags)
> if (av_find_info_tag(buf, sizeof(buf), "kmpreannounce", p)) {
> s->kmpreannounce = strtol(buf, NULL, 10);
> }
> + if (av_find_info_tag(buf, sizeof(buf), "snddropdelay", p)) {
> + s->snddropdelay = strtoll(buf, NULL, 10);
> + }
> #endif
> if (av_find_info_tag(buf, sizeof(buf), "mss", p)) {
> s->mss = strtol(buf, NULL, 10);
> --
> 1.8.3.1
>
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