[FFmpeg-devel] [PATCH] libavutil/timestamp.h: Fix loss of precision in timestamps for silencedetect on long files
Allan Cady
allancady at yahoo.com
Sun Apr 7 10:47:26 EEST 2019
[Second try submitting to the list. This patch now passes fate.]
When the silencedetect filter is run against long files, the output
timestamps gradually lose precision as the scan proceeds further into
the file. This is because the output is formatted (in
libavutil/timestamp.h) as "%.6g", which limits the total field
length. Eventually, for offsets greater than 100000 seconds (about 28
hours), fractions of a second disappear altogether, and the
timestamps are logged as whole seconds. This is insufficient
precision for my purposes. I propose changing the format to "%.6f",
which will give microsecond precision (probably overkill but safe)
for all timestamps regardless of offset.
The timestamp string length is limited to 32 characters
(AV_TS_MAX_STRING_SIZE), so this should still be plenty long enough
with the increased length (up to 10^25 seconds).
My interest is in fixing this problem for silencedetect, which
formats the timestamps by calling the macro av_ts2timestr, defined in
timestamp.h. Since av_ts2timestr is also used in many other places (I
count 21 c files), I have created a new macro, av_ts2timestr_format,
with a format string added as a parameter, and left the original
macro interface as is for other usages, to limit the scope of this
change. The same or similar change could be made for other cases
where better precision is desired.
-------------- next part --------------
From 5492506534bf863cbf1ee8f09a5e59b4ee111226 Mon Sep 17 00:00:00 2001
From: Allan Cady <allancady at yahoo.com>
Date: Sun, 7 Apr 2019 00:07:58 -0700
Subject: [PATCH] libavutil/timestamp.h: Fix loss of precision in timestamps
for silencedetect on long files
When the silencedetect filter is run against long files, the output
timestamps gradually lose precision as the scan proceeds further into
the file. This is because the output is formatted (in
libavutil/timestamp.h) as "%.6g", which limits the total field
length. Eventually, for offsets greater than 100000 seconds (about 28
hours), fractions of a second disappear altogether, and the
timestamps are logged as whole seconds. This is insufficient
precision for my purposes. I propose changing the format to "%.6f",
which will give microsecond precision (probably overkill but safe)
for all timestamps regardless of offset.
The timestamp string length is limited to 32 characters
(AV_TS_MAX_STRING_SIZE), so this should still be plenty long enough
with the increased length (up to 10^25 seconds).
My interest is in fixing this problem for silencedetect, which
formats the timestamps by calling the macro av_ts2timestr, defined in
timestamp.h. Since av_ts2timestr is also used in many other places (I
count 21 c files), I have created a new macro, av_ts2timestr_format,
with a format string added as a parameter, and left the original
macro interface as is for other usages, to limit the scope of this
change. The same or similar change could be made for other cases
where better precision is desired.
---
libavfilter/af_silencedetect.c | 14 ++++++++------
libavutil/timestamp.h | 13 ++++++++-----
tests/ref/fate/filter-metadata-silencedetect | 2 +-
3 files changed, 17 insertions(+), 12 deletions(-)
diff --git a/libavfilter/af_silencedetect.c b/libavfilter/af_silencedetect.c
index 3a71f39..2da8dbe 100644
--- a/libavfilter/af_silencedetect.c
+++ b/libavfilter/af_silencedetect.c
@@ -32,6 +32,8 @@
#include "avfilter.h"
#include "internal.h"
+const char TIMESTAMP_FMT_SILENCEDETECT[] = "%.6f";
+
typedef struct SilenceDetectContext {
const AVClass *class;
double noise; ///< noise amplitude ratio
@@ -86,11 +88,11 @@ static av_always_inline void update(SilenceDetectContext *s, AVFrame *insamples,
s->start[channel] = insamples->pts + av_rescale_q(current_sample / s->channels + 1 - nb_samples_notify * s->independent_channels / s->channels,
(AVRational){ 1, s->last_sample_rate }, time_base);
set_meta(insamples, s->mono ? channel + 1 : 0, "silence_start",
- av_ts2timestr(s->start[channel], &time_base));
+ av_ts2timestr_fmt(s->start[channel], &time_base, TIMESTAMP_FMT_SILENCEDETECT));
if (s->mono)
av_log(s, AV_LOG_INFO, "channel: %d | ", channel);
av_log(s, AV_LOG_INFO, "silence_start: %s\n",
- av_ts2timestr(s->start[channel], &time_base));
+ av_ts2timestr_fmt(s->start[channel], &time_base, TIMESTAMP_FMT_SILENCEDETECT));
}
}
} else {
@@ -101,15 +103,15 @@ static av_always_inline void update(SilenceDetectContext *s, AVFrame *insamples,
int64_t duration_ts = end_pts - s->start[channel];
if (insamples) {
set_meta(insamples, s->mono ? channel + 1 : 0, "silence_end",
- av_ts2timestr(end_pts, &time_base));
+ av_ts2timestr_fmt(end_pts, &time_base, TIMESTAMP_FMT_SILENCEDETECT));
set_meta(insamples, s->mono ? channel + 1 : 0, "silence_duration",
- av_ts2timestr(duration_ts, &time_base));
+ av_ts2timestr_fmt(duration_ts, &time_base, TIMESTAMP_FMT_SILENCEDETECT));
}
if (s->mono)
av_log(s, AV_LOG_INFO, "channel: %d | ", channel);
av_log(s, AV_LOG_INFO, "silence_end: %s | silence_duration: %s\n",
- av_ts2timestr(end_pts, &time_base),
- av_ts2timestr(duration_ts, &time_base));
+ av_ts2timestr_fmt(end_pts, &time_base, TIMESTAMP_FMT_SILENCEDETECT),
+ av_ts2timestr_fmt(duration_ts, &time_base, TIMESTAMP_FMT_SILENCEDETECT));
}
s->nb_null_samples[channel] = 0;
s->start[channel] = INT64_MIN;
diff --git a/libavutil/timestamp.h b/libavutil/timestamp.h
index e082f01..fd9baaf 100644
--- a/libavutil/timestamp.h
+++ b/libavutil/timestamp.h
@@ -31,6 +31,7 @@
#endif
#define AV_TS_MAX_STRING_SIZE 32
+#define TIMESTAMP_FMT_GENERAL "%.6g"
/**
* Fill the provided buffer with a string containing a timestamp
@@ -55,24 +56,26 @@ static inline char *av_ts_make_string(char *buf, int64_t ts)
/**
* Fill the provided buffer with a string containing a timestamp time
- * representation.
+ * representation, allowing format specification.
*
* @param buf a buffer with size in bytes of at least AV_TS_MAX_STRING_SIZE
* @param ts the timestamp to represent
* @param tb the timebase of the timestamp
+ * @param format format string for timestamp output, e.g. "%.5f".
* @return the buffer in input
*/
-static inline char *av_ts_make_time_string(char *buf, int64_t ts, AVRational *tb)
+static inline char *av_ts_make_time_string_format(char *buf, int64_t ts, AVRational *tb, const char *format)
{
if (ts == AV_NOPTS_VALUE) snprintf(buf, AV_TS_MAX_STRING_SIZE, "NOPTS");
- else snprintf(buf, AV_TS_MAX_STRING_SIZE, "%.6g", av_q2d(*tb) * ts);
+ else snprintf(buf, AV_TS_MAX_STRING_SIZE, format, av_q2d(*tb) * ts);
return buf;
}
/**
- * Convenience macro, the return value should be used only directly in
+ * Convenience macros, the return value should be used only directly in
* function arguments but never stand-alone.
*/
-#define av_ts2timestr(ts, tb) av_ts_make_time_string((char[AV_TS_MAX_STRING_SIZE]){0}, ts, tb)
+#define av_ts2timestr_fmt(ts, tb, fmt) av_ts_make_time_string_format((char[AV_TS_MAX_STRING_SIZE]){0}, ts, tb, fmt)
+#define av_ts2timestr(ts, tb) av_ts_make_time_string_format((char[AV_TS_MAX_STRING_SIZE]){0}, ts, tb, TIMESTAMP_FMT_GENERAL)
#endif /* AVUTIL_TIMESTAMP_H */
diff --git a/tests/ref/fate/filter-metadata-silencedetect b/tests/ref/fate/filter-metadata-silencedetect
index 16a9d07..5d8063c 100644
--- a/tests/ref/fate/filter-metadata-silencedetect
+++ b/tests/ref/fate/filter-metadata-silencedetect
@@ -1,5 +1,5 @@
pkt_pts=0|tag:lavfi.silence_duration=0.523107|tag:lavfi.silence_end=0.690023|tag:lavfi.silence_start=0.736417
-pkt_pts=46080|tag:lavfi.silence_start=1.27626|tag:lavfi.silence_end=1.80751|tag:lavfi.silence_duration=0.531247
+pkt_pts=46080|tag:lavfi.silence_start=1.276259|tag:lavfi.silence_end=1.807506|tag:lavfi.silence_duration=0.531247
pkt_pts=92160
pkt_pts=138240
pkt_pts=184320
--
2.7.4
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