Re: [FFmpeg-devel] [PATCH] avformat/hls:use EXT-X-START instead of live_start_index if it's in playlist

[少宇李 <wolfleekay@gmail.com>]

>
>
> Hi, Steven


I got it.

User could use "live_start_index" option even if #EXT-X-START in the
playlist.

I changed the priority about #EXT-X-START/live_start_index,

this is new bellow:

---
 libavformat/hls.c | 69 +++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 64 insertions(+), 5 deletions(-)

diff --git a/libavformat/hls.c b/libavformat/hls.c
index b736f093a9..309471efce 100644
--- a/libavformat/hls.c
+++ b/libavformat/hls.c
@@ -120,6 +120,8 @@ struct playlist {
     enum PlaylistType type;
     int64_t target_duration;
     int64_t start_seq_no;
+    int time_offset_flag;
+    int64_t start_time_offset;
     int n_segments;
     struct segment **segments;
     int needed;
@@ -741,6 +743,7 @@ static int parse_playlist(HLSContext *c, const char
*url,
     struct segment **prev_segments = NULL;
     int prev_n_segments = 0;
     int64_t prev_start_seq_no = -1;
+    const char *p;

     if (is_http && !in && c->http_persistent && c->playlist_pb) {
         in = c->playlist_pb;
@@ -889,6 +892,18 @@ static int parse_playlist(HLSContext *c, const char
*url,
                 cur_init_section->key = NULL;
             }

+        } else if (av_strstart(line, "#EXT-X-START:", &ptr)) {
+            ret = ensure_playlist(c, &pls, url);
+            if (ret < 0) {
+                goto fail;
+            }
+            if (av_strstart(ptr, "TIME-OFFSET=", &p)) {
+                float offset = strtof(p, NULL);
+                pls->start_time_offset = offset * AV_TIME_BASE;
+                pls->time_offset_flag = 1;
+            } else {
+                goto fail;
+            }
         } else if (av_strstart(line, "#EXT-X-ENDLIST", &ptr)) {
             if (pls)
                 pls->finished = 1;
@@ -1721,10 +1736,54 @@ static int64_t select_cur_seq_no(HLSContext *c,
struct playlist *pls)

         /* If this is a live stream, start live_start_index segments from
the
          * start or end */
-        if (c->live_start_index < 0)
-            return pls->start_seq_no + FFMAX(pls->n_segments +
c->live_start_index, 0);
-        else
-            return pls->start_seq_no + FFMIN(c->live_start_index,
pls->n_segments - 1);
+        if (c->live_start_index != INT_MIN) {
+            if (c->live_start_index < 0)
+                return pls->start_seq_no + FFMAX(pls->n_segments +
+                                                c->live_start_index, 0);
+            else
+                return pls->start_seq_no + FFMIN(c->live_start_index,
+                                                pls->n_segments - 1);
+        } else if (c->live_start_index == INT_MIN &&
!pls->time_offset_flag) {
+            return pls->start_seq_no + FFMAX(pls->n_segments - 3, 0);
+        } else {
+            /* If playlist indicate a TIME-OFFSET and user not use
live_start_index,
+             * need to recalculate seq_no */
+            int i;
+            int64_t start_timestamp;
+            int64_t playlist_duration = 0;
+            int64_t cur_timestamp = c->cur_timestamp == AV_NOPTS_VALUE ? 0
:
+                                    c->cur_timestamp;
+
+            for (i = 0; i < pls->n_segments; i++) {
+                playlist_duration += pls->segments[i]->duration;
+            }
+            /* If the absolute value of TIME-OFFSET exceeds
+             * the duration of the playlist, it indicates either the end
of the
+             * playlist (if positive) or the beginning of the playlist (if
+             * negative). */
+            if (pls->start_time_offset >=0 &&
+                pls->start_time_offset > playlist_duration)
+                start_timestamp = cur_timestamp + playlist_duration;
+            else if (pls->start_time_offset >= 0 &&
+                        pls->start_time_offset <= playlist_duration)
+                start_timestamp = cur_timestamp + pls->start_time_offset;
+            else if (pls->start_time_offset < 0 &&
+                        pls->start_time_offset < -playlist_duration)
+                start_timestamp = cur_timestamp;
+            else if (pls->start_time_offset < 0 &&
+                        pls->start_time_offset > -playlist_duration)
+                start_timestamp = cur_timestamp + playlist_duration +
+                                    pls->start_time_offset;
+            else
+                start_timestamp = cur_timestamp;
+
+            find_timestamp_in_playlist(c, pls, start_timestamp, &seq_no,
NULL);
+            av_log(c, AV_LOG_DEBUG, "start_timestamp: %" PRId64
+                                    "cur_timestamp:%" PRId64
+                                    "cur_seq_no:%" PRId64 "\n",
+                                    start_timestamp, cur_timestamp,
seq_no);
+            return seq_no;
+        }
     }

     /* Otherwise just start on the first segment. */
@@ -2475,7 +2534,7 @@ static int hls_probe(const AVProbeData *p)
 #define FLAGS AV_OPT_FLAG_DECODING_PARAM
 static const AVOption hls_options[] = {
     {"live_start_index", "segment index to start live streams at (negative
values are from the end)",
-        OFFSET(live_start_index), AV_OPT_TYPE_INT, {.i64 = -3}, INT_MIN,
INT_MAX, FLAGS},
+        OFFSET(live_start_index), AV_OPT_TYPE_INT, {.i64 = INT_MIN},
INT_MIN, INT_MAX, FLAGS},
     {"allowed_extensions", "List of file extensions that hls is allowed to
access",
         OFFSET(allowed_extensions), AV_OPT_TYPE_STRING,
         {.str =
"3gp,aac,avi,ac3,eac3,flac,mkv,m3u8,m4a,m4s,m4v,mpg,mov,mp2,mp3,mp4,mpeg,mpegts,ogg,ogv,oga,ts,vob,wav"},
-- 
2.24.1 (Apple Git-126)


Thanks Steven
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