From: "Allan Cady" <allanc...@yahoo.com>
I propose changing the format to "%.6f", which will
give microsecond precision for all timestamps, regardless of
offset. Trailing zeros can be trimmed from the fraction, without
losing precision. If the length of the fixed-precision formatted
timestamp exceeds the length of the allocated buffer
(AV_TS_MAX_STRING_SIZE, currently 32, less one for the
terminating null), then we can fall back to scientific notation, though
this seems almost certain to never occur, because 32 characters would
allow a maximum timestamp value of (32 - 1 - 6 - 1) = 24 characters.
By my calculation, 10^24 seconds is about six orders of magnitude
greater than the age of the universe.
The fix proposed here follows the following logic:
1) Try formatting the number of seconds using "%.6f". This will
always result in a string with six decimal digits in the fraction,
possibly including trailing zeros. (e.g. "897234.73200").
2) Check if that string would overflow the buffer. If it would, then
format it using scientific notation ("%.8g").
3) If the original fixed-point format fits, then trim any trailing
zeros and decimal point, and return that result.
Making this change broke two fate tests, filter-metadata-scdet,
and filter-metadata-silencedetect. To correct this, I've modified
tests/ref/fate/filter-metadata-scdet and
tests/ref/fate/filter-metadata-silencedetect to match the
new output.
Signed-off-by: Allan Cady <allanc...@yahoo.com>
---
libavutil/timestamp.h | 53 +++++++++++++++++++-
tests/ref/fate/filter-metadata-scdet | 12 ++---
tests/ref/fate/filter-metadata-silencedetect | 2 +-
3 files changed, 58 insertions(+), 9 deletions(-)
diff --git a/libavutil/timestamp.h b/libavutil/timestamp.h
index 2b37781eba..2f04f9bb2b 100644
--- a/libavutil/timestamp.h
+++ b/libavutil/timestamp.h
@@ -25,6 +25,7 @@
#define AVUTIL_TIMESTAMP_H
#include "avutil.h"
+#include <stdbool.h>
#if defined(__cplusplus) && !defined(__STDC_FORMAT_MACROS) && !defined(PRId64)
#error missing -D__STDC_FORMAT_MACROS / #define __STDC_FORMAT_MACROS
@@ -53,6 +54,32 @@ static inline char *av_ts_make_string(char *buf, int64_t ts)
*/
#define av_ts2str(ts) av_ts_make_string((char[AV_TS_MAX_STRING_SIZE]){0}, ts)
+/**
+ * Strip trailing zeros and decimal point from a string. Performed
+ * in-place on input buffer. For local use only by av_ts_make_time_string.
+ *
+ * e.g.:
+ * "752.378000" -> "752.378"
+ * "4.0" -> "4"
+ * "97300" -> "97300"
+ */
+static inline void av_ts_strip_trailing_zeros_and_decimal_point(char *str) {
+ if (strchr(str, '.'))
+ {
+ int i;
+ for (i = strlen(str) - 1; i >= 0 && str[i] == '0'; i--) {
+ str[i] = '\0';
+ }
+
+ // Remove decimal point if it's the last character
+ if (i >= 0 && str[i] == '.') {
+ str[i] = '\0';
+ }
+
+ // String was modified in place; no need for return value.
+ }
+}
+
/**
* Fill the provided buffer with a string containing a timestamp time
* representation.
@@ -65,8 +92,30 @@ static inline char *av_ts_make_string(char *buf, int64_t ts)
static inline char *av_ts_make_time_string(char *buf, int64_t ts,
const AVRational *tb)
{
- 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);
+ if (ts == AV_NOPTS_VALUE)
+ {
+ snprintf(buf, AV_TS_MAX_STRING_SIZE, "NOPTS");
+ }
+ else
+ {
+ const int max_fraction_digits = 6;
+
+ // Convert 64-bit timestamp to double, using rational timebase
+ double seconds = av_q2d(*tb) * ts;
+
+ int length = snprintf(NULL, 0, "%.*f", max_fraction_digits, seconds);
+ if (length <= AV_TS_MAX_STRING_SIZE - 1)
+ {
+ snprintf(buf, AV_TS_MAX_STRING_SIZE, "%.*f", max_fraction_digits,
seconds);
+ av_ts_strip_trailing_zeros_and_decimal_point(buf);
+ }
+ else
+ {
+ snprintf(buf, AV_TS_MAX_STRING_SIZE, "%.8g", seconds);
+ }
+
+ }
+
return buf;
}
