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ffmpeg: add option readrate

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Allows to read inputs at arbitrary rates.
-re is equivalent to -readrate 1

Tested with -copyts {+ start_at_zero}, -ss, streamcopied & decoded streams.
This commit is contained in:
Gyan Doshi 2021-07-16 17:59:39 +05:30
parent 075157ec86
commit c320b78e95
4 changed files with 41 additions and 11 deletions
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21
doc/ffmpeg.texi
View File

@ -1575,14 +1575,21 @@ Exit after ffmpeg has been running for @var{duration} seconds in CPU user time.
Dump each input packet to stderr.
@item -hex (@emph{global})
When dumping packets, also dump the payload.
@item -readrate @var{speed} (@emph{input})
Limit input read speed.
Its value is a floating-point positive number which represents the maximum duration of
media, in seconds, that should be ingested in one second of wallclock time.
Default value is zero and represents no imposed limitation on speed of ingestion.
Value @code{1} represents real-time speed and is equivalent to @code{-re}.
Mainly used to simulate a capture device or live input stream (e.g. when reading from a file).
Should not be used with a low value when input is an actual capture device or live stream as
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. Mainly used to simulate a grab device,
or live input stream (e.g. when reading from a file). Should not be used
with actual grab devices or live input streams (where it can cause packet
loss).
By default @command{ffmpeg} attempts to read the input(s) as fast as possible.
This option will slow down the reading of the input(s) to the native frame rate
of the input(s). It is useful for real-time output (e.g. live streaming).
Read input at native frame rate. This is equivalent to setting @code{-readrate 1}.
@item -vsync @var{parameter}
Video sync method.
For compatibility reasons old values can be specified as numbers.

13
fftools/ffmpeg.c
View File

@ -3765,7 +3765,7 @@ static int transcode_init(void)
/* init framerate emulation */
for (i = 0; i < nb_input_files; i++) {
InputFile *ifile = input_files[i];
if (ifile->rate_emu)
if (ifile->readrate || ifile->rate_emu)
for (j = 0; j < ifile->nb_streams; j++)
input_streams[j + ifile->ist_index]->start = av_gettime_relative();
}
@ -4225,12 +4225,19 @@ static int get_input_packet_mt(InputFile *f, AVPacket **pkt)
static int get_input_packet(InputFile *f, AVPacket **pkt)
{
if (f->rate_emu) {
if (f->readrate || f->rate_emu) {
int i;
int64_t file_start = copy_ts * (
(f->ctx->start_time != AV_NOPTS_VALUE ? f->ctx->start_time * !start_at_zero : 0) +
(f->start_time != AV_NOPTS_VALUE ? f->start_time : 0)
);
float scale = f->rate_emu ? 1.0 : f->readrate;
for (i = 0; i < f->nb_streams; i++) {
InputStream *ist = input_streams[f->ist_index + i];
if (!ist->nb_packets) continue;
int64_t stream_ts_offset = FFMAX(ist->first_dts != AV_NOPTS_VALUE ? ist->first_dts : 0, file_start);
int64_t pts = av_rescale(ist->dts, 1000000, AV_TIME_BASE);
int64_t now = av_gettime_relative() - ist->start;
int64_t now = (av_gettime_relative() - ist->start)*scale + stream_ts_offset;
if (pts > now)
return AVERROR(EAGAIN);
}

2
fftools/ffmpeg.h
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@ -119,6 +119,7 @@ typedef struct OptionsContext {
int64_t input_ts_offset;
int loop;
int rate_emu;
float readrate;
int accurate_seek;
int thread_queue_size;
@ -418,6 +419,7 @@ typedef struct InputFile {
from ctx.nb_streams if new streams appear during av_read_frame() */
int nb_streams_warn; /* number of streams that the user was warned of */
int rate_emu;
float readrate;
int accurate_seek;
AVPacket *pkt;

16
fftools/ffmpeg_opt.c
View File

@ -1286,6 +1286,17 @@ static int open_input_file(OptionsContext *o, const char *filename)
f->loop = o->loop;
f->duration = 0;
f->time_base = (AVRational){ 1, 1 };
f->readrate = o->readrate ? o->readrate : 0.0;
if (f->readrate < 0.0f) {
av_log(NULL, AV_LOG_ERROR, "Option -readrate for Input #%d is %0.3f; it must be non-negative.\n", nb_input_files, f->readrate);
exit_program(1);
}
if (f->readrate && f->rate_emu) {
av_log(NULL, AV_LOG_WARNING, "Both -readrate and -re set for Input #%d. Using -readrate %0.3f.\n", nb_input_files, f->readrate);
f->rate_emu = 0;
}
f->pkt = av_packet_alloc();
if (!f->pkt)
exit_program(1);
@ -3507,7 +3518,10 @@ const OptionDef options[] = {
"when dumping packets, also dump the payload" },
{ "re", OPT_BOOL | OPT_EXPERT | OPT_OFFSET |
OPT_INPUT, { .off = OFFSET(rate_emu) },
"read input at native frame rate", "" },
"read input at native frame rate; equivalent to -readrate 1", "" },
{ "readrate", HAS_ARG | OPT_FLOAT | OPT_OFFSET |
OPT_EXPERT | OPT_INPUT, { .off = OFFSET(readrate) },
"read input at specified rate", "speed" },
{ "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" },