Implemented is the -irb <seconds> flag (i.e. "initial read burst") that
causes ffmpeg to read the specified number of seconds of input before a
given readrate starts to be enforced. All inputs have to reach this
point before the readrate is enforced. The reason for this change is,
in the scenario of live-streaming by transcoding from an pre-recorded or
delayed source to an HLS or DASH webroot, we can more quickly prime the
system of the first few seconds before the real-world read rate is
imposed. Else, one must wait for an entire segment length before the
data can be fetched from the web server.
Signed-off-by: Davy Durham <ddur...@users.sourceforge.net>
---
doc/ffmpeg.texi | 2 ++
fftools/ffmpeg.c | 3 ++-
fftools/ffmpeg.h | 2 ++
fftools/ffmpeg_opt.c | 13 +++++++++++++
4 files changed, 19 insertions(+), 1 deletion(-)
diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
index 767df69b7f..16ab1a336f 100644
--- a/doc/ffmpeg.texi
+++ b/doc/ffmpeg.texi
@@ -1633,6 +1633,8 @@ it may cause packet loss.
It is useful for when flow speed of output packets is important, such
as live streaming.
@item -re (@emph{input})
Read input at native frame rate. This is equivalent to setting
@code{-readrate 1}.
+@item -irb @var{seconds}
+Set an initial read burst time, in seconds, after which any specified
readrate will be enforced.
@item -vsync @var{parameter} (@emph{global})
@itemx -fps_mode[:@var{stream_specifier}] @var{parameter}
(@emph{output,per-stream})
Set video sync method / framerate mode. vsync is applied to all output
video streams
diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
index e7384f052a..e4697c8772 100644
--- a/fftools/ffmpeg.c
+++ b/fftools/ffmpeg.c
@@ -3768,6 +3768,7 @@ static int get_input_packet(InputFile *f, AVPacket
**pkt)
(f->start_time != AV_NOPTS_VALUE ?
f->start_time : 0)
);
float scale = f->rate_emu ? 1.0 : f->readrate;
+ int64_t burst_until = AV_TIME_BASE * f->initial_read_burst;
for (i = 0; i < f->nb_streams; i++) {
InputStream *ist = input_streams[f->ist_index + i];
int64_t stream_ts_offset, pts, now;
@@ -3775,7 +3776,7 @@ static int get_input_packet(InputFile *f, AVPacket
**pkt)
stream_ts_offset = FFMAX(ist->first_dts != AV_NOPTS_VALUE
? ist->first_dts : 0, file_start);
pts = av_rescale(ist->dts, 1000000, AV_TIME_BASE);
now = (av_gettime_relative() - ist->start) * scale +
stream_ts_offset;
- if (pts > now)
+ if (pts - burst_until > now)
return AVERROR(EAGAIN);
}
}
diff --git a/fftools/ffmpeg.h b/fftools/ffmpeg.h
index 391a35cf50..aa079ab3e9 100644
--- a/fftools/ffmpeg.h
+++ b/fftools/ffmpeg.h
@@ -116,6 +116,7 @@ typedef struct OptionsContext {
int loop;
int rate_emu;
float readrate;
+ double initial_read_burst;
int accurate_seek;
int thread_queue_size;
int input_sync_ref;
@@ -422,6 +423,7 @@ typedef struct InputFile {
int nb_streams_warn; /* number of streams that the user was
warned of */
int rate_emu;
float readrate;
+ double initial_read_burst;
int accurate_seek;
AVPacket *pkt;
diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
index 6e18a4a23e..57aa4929fa 100644
--- a/fftools/ffmpeg_opt.c
+++ b/fftools/ffmpeg_opt.c
@@ -1378,6 +1378,16 @@ static int open_input_file(OptionsContext *o,
const char *filename)
f->rate_emu = 0;
}
+ f->initial_read_burst = o->initial_read_burst ?
o->initial_read_burst : 0.0;
+ if (f->initial_read_burst < 0.0) {
+ av_log(NULL, AV_LOG_ERROR, "Option -irb for Input #%d is %0.3f;
it must be non-negative.\n", nb_input_files, f->initial_read_burst);
+ exit_program(1);
+ }
+ if ((!f->readrate && !f->rate_emu) && f->initial_read_burst) {
+ av_log(NULL, AV_LOG_WARNING, "Option -irb ignored since neither
-readrate nor -re were given\n");
+ f->initial_read_burst = 0;
+ }
+
f->pkt = av_packet_alloc();
if (!f->pkt)
exit_program(1);
@@ -3734,6 +3744,9 @@ const OptionDef options[] = {
{ "readrate", HAS_ARG | OPT_FLOAT | OPT_OFFSET |
OPT_EXPERT | OPT_INPUT, {
.off = OFFSET(readrate) },
"read input at specified rate", "speed" },
+ { "irb", HAS_ARG | OPT_DOUBLE | OPT_OFFSET |
+ OPT_EXPERT | OPT_INPUT, {
.off = OFFSET(initial_read_burst) },
+ "The initial amount of input to burst read before imposing any
readrate", "seconds" },
{ "target", HAS_ARG | OPT_PERFILE | OPT_OUTPUT, {
.func_arg = opt_target },
"specify target file type (\"vcd\", \"svcd\", \"dvd\", \"dv\"
or \"dv50\" "
"with optional prefixes \"pal-\", \"ntsc-\" or \"film-\")",
"type" },
--
2.25.1
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