lavf/segment: add -segment_time_delta option

doc/muxers.texi

@@ -474,6 +474,28 @@ the segment start and end time expressed in seconds.
 Default value is "flat".
 @item segment_time @var{time}
 Set segment duration to @var{time}. Default value is "2".
+@item segment_time_delta @var{delta}
+Specify the accuracy time when selecting the start time for a
+segment. Default value is "0".
+
+When delta is specified a key-frame will start a new segment if its
+PTS satisfies the relation:
+@example
+PTS >= start_time - time_delta
+@end example
+
+This option is useful when splitting video content, which is always
+split at GOP boundaries, in case a key frame is found just before the
+specified split time.
+
+In particular may be used in combination with the @file{ffmpeg} option
+@var{force_key_frames}. The key frame times specified by
+@var{force_key_frames} may not be set accurately because of rounding
+issues, with the consequence that a key frame time may result set just
+before the specified time. For constant frame rate videos a value of
+1/2*@var{frame_rate} should address the worst case mismatch between
+the specified time and the time set by @var{force_key_frames}.
+
 @item segment_times @var{times}
 Specify a list of split points. @var{times} contains a list of comma
 separated duration specifications, in increasing order.
@@ -499,6 +521,18 @@ points specified by the @var{segment_times} option:
 ffmpeg -i in.mkv -codec copy -map 0 -f segment -segment_list_type ext -segment_list out.list -segment_list_size 0 -segment_times 1,2,3,5,8,13,21 out%03d.nut
 @end example
 
+@item
+As the example above, but use the @code{ffmpeg} @var{force_key_frames}
+option to force key frames in the input at the specified location, together
+with the segment option @var{segment_time_delta} to account for
+possible roundings operated when setting key frame times.
+@example
+ffmpeg -i in.mkv -force_key_frames 1,2,3,5,8,13,21 -vcodec mpeg4 -acodec pcm_s16le -map 0 \
+-f segment -segment_list_type ext -segment_list out.list -segment_list_size 0 -segment_times 1,2,3,5,8,13,21 -segment_time_delta 0.05 out%03d.nut
+@end example
+In order to force key frames on the input file, transcoding is
+required.
+
 @item
 To convert the @file{in.mkv} to TS segments using the @code{libx264}
 and @code{libfaac} encoders:

libavformat/segment.c

@@ -52,6 +52,8 @@ typedef struct {
     char *times_str;       ///< segment times specification string
     int64_t *times;        ///< list of segment interval specification
     int nb_times;          ///< number of elments in the times array
+    char *time_delta_str;  ///< approximation value duration used for the segment times
+    int64_t time_delta;
     int has_video;
     double start_time, end_time;
 } SegmentContext;
@@ -222,6 +224,15 @@ static int seg_write_header(AVFormatContext *s)
         }
     }
 
+    if (seg->time_delta_str) {
+        if ((ret = av_parse_time(&seg->time_delta, seg->time_delta_str, 1)) < 0) {
+            av_log(s, AV_LOG_ERROR,
+                   "Invalid time duration specification '%s' for delta option\n",
+                   seg->time_delta_str);
+            return ret;
+        }
+    }
+
     oc = avformat_alloc_context();
 
     if (!oc)
@@ -304,7 +315,7 @@ static int seg_write_packet(AVFormatContext *s, AVPacket *pkt)
     /* if the segment has video, start a new segment *only* with a key video frame */
     if ((st->codec->codec_type == AVMEDIA_TYPE_VIDEO || !seg->has_video) &&
         av_compare_ts(pkt->pts, st->time_base,
-                      end_pts, AV_TIME_BASE_Q) >= 0 &&
+                      end_pts-seg->time_delta, AV_TIME_BASE_Q) >= 0 &&
         pkt->flags & AV_PKT_FLAG_KEY) {
 
         av_log(s, AV_LOG_DEBUG, "Next segment starts with packet stream:%d pts:%"PRId64" pts_time:%f\n",
@@ -359,6 +370,7 @@ static const AVOption options[] = {
     { "flat", "flat format",     0, AV_OPT_TYPE_CONST, {.dbl=LIST_TYPE_FLAT }, INT_MIN, INT_MAX, 0, "list_type" },
     { "ext",  "extended format", 0, AV_OPT_TYPE_CONST, {.dbl=LIST_TYPE_EXT  }, INT_MIN, INT_MAX, 0, "list_type" },
     { "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_str), AV_OPT_TYPE_STRING, {.str = "0"}, 0, 0, E },
     { "segment_times",     "set segment split time points",              OFFSET(times_str),AV_OPT_TYPE_STRING,{.str = NULL},  0, 0,       E },
     { "segment_wrap",      "set number after which the index wraps",     OFFSET(wrap),    AV_OPT_TYPE_INT,    {.dbl = 0},     0, INT_MAX, E },
     { NULL },

libavformat/version.h

@@ -31,7 +31,7 @@
 
 #define LIBAVFORMAT_VERSION_MAJOR 54
 #define LIBAVFORMAT_VERSION_MINOR 15
-#define LIBAVFORMAT_VERSION_MICRO 103
+#define LIBAVFORMAT_VERSION_MICRO 104
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \