[FFmpeg-devel] [PATCH 2/2] lavf/segment: add new option segment_clocktime_wrap_duration

[Stefano Sabatini]

On date Monday 2016-01-18 21:56:30 +0100, Marton Balint encoded:
> This option can force the segmenter to only start a new segment if a packet
> reaches the muxer whithin the specified duration after the segmenting clock
> time, which makes it more resilient to backward local time jumps, such as leap
> seconds or transition to standard time from daylight savings time.
> 
> Signed-off-by: Marton Balint <cus at passwd.hu>
> ---
>  doc/muxers.texi       | 13 +++++++++++++
>  libavformat/segment.c |  4 +++-
>  2 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/doc/muxers.texi b/doc/muxers.texi
> index c304221..2ed468e 100644
> --- a/doc/muxers.texi
> +++ b/doc/muxers.texi
> @@ -1110,6 +1110,19 @@ create files at 12:05, 12:20, 12:35, etc.
>  
>  Default value is "0".
>  
> + at item segment_clocktime_wrap_duration @var{duration}
> +By setting this option you can force the segmenter to only start a new segment
> +if a packet reaches the muxer whithin the specified duration after the

whithin => within

> +segmenting clock time.

Simpler:
Force the segmenter to only start ... 

> This way you can make the segmenter more resilient to
> +backward local time jumps, such as leap seconds or transition to standard time
> +from daylight savings time.
> +

> +Assuming that the delay between the packets of your source is less than 0.5
> +second you can detect a leap second by specifying 0.5 as the duration.
> +
> +Default is the maximum possible duration which means starting a new segment
> +regardless of the elapsed time since the last clock time.
> +
>  @item segment_time_delta @var{delta}
>  Specify the accuracy time when selecting the start time for a
>  segment, expressed as a duration specification. Default value is "0".
> diff --git a/libavformat/segment.c b/libavformat/segment.c
> index bf7a8fc..d92b9c3 100644
> --- a/libavformat/segment.c
> +++ b/libavformat/segment.c
> @@ -83,6 +83,7 @@ typedef struct SegmentContext {
>  
>      int use_clocktime;    ///< flag to cut segments at regular clock time
>      int64_t clocktime_offset; //< clock offset for cutting the segments at regular clock time
> +    int64_t clocktime_wrap_duration; //< wrapping duration considered for starting a new segment
>      int64_t last_val;      ///< remember last time for wrap around detection
>      int64_t last_cut;      ///< remember last cut
>      int cut_pending;
> @@ -784,7 +785,7 @@ static int seg_write_packet(AVFormatContext *s, AVPacket *pkt)
>              localtime_r(&sec, &ti);
>              usecs = (int64_t)(ti.tm_hour * 3600 + ti.tm_min * 60 + ti.tm_sec) * 1000000 + (avgt % 1000000);
>              wrapped_val = (usecs + seg->clocktime_offset) % seg->time;
> -            if (seg->last_cut != usecs && wrapped_val < seg->last_val) {
> +            if (seg->last_cut != usecs && wrapped_val < seg->last_val && wrapped_val < seg->clocktime_wrap_duration) {
>                  seg->cut_pending = 1;
>                  seg->last_cut = usecs;
>              }
> @@ -935,6 +936,7 @@ static const AVOption options[] = {
>  
>      { "segment_atclocktime",      "set segment to be cut at clocktime",  OFFSET(use_clocktime), AV_OPT_TYPE_BOOL, {.i64 = 0}, 0, 1, E},
>      { "segment_clocktime_offset", "set segment clocktime offset",        OFFSET(clocktime_offset), AV_OPT_TYPE_DURATION, {.i64 = 0}, 0, 86400, E},
> +    { "segment_clocktime_wrap_duration", "set segment clocktime wrapping duration", OFFSET(clocktime_wrap_duration), AV_OPT_TYPE_DURATION, {.i64 = INT_MAX}, 0, INT_MAX, E},
>      { "segment_time",      "set segment duration",                       OFFSET(time_str),AV_OPT_TYPE_STRING, {.str = NULL},  0, 0,       E },
>      { "segment_time_delta","set approximation value used for the segment times", OFFSET(time_delta), AV_OPT_TYPE_DURATION, {.i64 = 0}, 0, 0, E },
>      { "segment_times",     "set segment split time points",              OFFSET(times_str),AV_OPT_TYPE_STRING,{.str = NULL},  0, 0,       E },
> -- 
> 2.6.2

LGTM otherwise, although I wonder if we could provide a more robust
mechanism to detect such issues.
-- 
FFmpeg = Faithful and Foolish Mournful Pitiful Elected Gargoyle