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>]

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Hi Steven,

Please review code.

I changed code, but I still have a question.
If EXT-X-START tag in playlist and users set live_start_index, the
live_start_index will not work
for current codes, which makes maybe users confused.
Is that OK?

In other hand, if make live_start_index valid when EXT-X-START tag in
playlist, maybe live_start_index needs a flag, or
make live_start_index default value is INT_MIN to distinguish.
becuase the live_start_index default value is -3, I have no idea to
distinguish users action or
default value when live_start_index=-3.

May I need to set default value=INT_MIN as live_start_index default value?
And only when does not exist EXT-X-START
tag in playlist, make live_start_index = -3 or users's configuration value.
I have no idea which is better~

Thanks a lot!

Steven Liu <lingjiujianke@gmail.com> 于2022年6月24日周五 14:21写道：

> 少宇李 <wolfleekay@gmail.com> 于2022年6月24日周五 11:58写道：
> >>
> >>
> >> 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) {
> Maybe you should not change current logic.
> You can just add  about process EXT-X-START sence,.
> For example:
> compute the start_seq_no and save the value to a temp varible and
> don't return immediately, check the third scence which get EXT-X-START
> tag from playlist.
> process the temp varible after start_seq_no compute from
> live_start_index or EXT-X-START.
>
> > +            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},
> This is unnecessary， because the default -3 is ok and be using by
> users from many years ago.
>
> >      {"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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From 1e45fb3facf5cfc8c67828b37b0bbaa994c2ab03 Mon Sep 17 00:00:00 2001
From: Li Kai <wolfleekay@gmail.com>
Date: Thu, 23 Jun 2022 00:55:38 +0800
Subject: Re: [FFmpeg-devel] [PATCH] avformat/hls:use EXT-X-START instead of live_start_index if it's in playlist

Signed-off-by: Li Kai <wolfleekay@gmail.com>
---
 libavformat/hls.c | 55 +++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 53 insertions(+), 2 deletions(-)

diff --git a/libavformat/hls.c b/libavformat/hls.c
index 8204f55df3..bfb20f6492 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;
@@ -1722,9 +1737,45 @@ 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);
+            seq_no = 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);
+            seq_no = pls->start_seq_no + FFMIN(c->live_start_index,
+                                            pls->n_segments - 1);
+
+        /* If #EXT-X-START in playlist, need to recalculate */
+        if (pls->time_offset_flag) {
+            int64_t start_timestamp;
+            int64_t playlist_duration = 0;
+            int64_t cur_timestamp = c->cur_timestamp == AV_NOPTS_VALUE ? 0 :
+                                    c->cur_timestamp;
+
+            for (int 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);
+        }
+        return seq_no;
     }
 
     /* Otherwise just start on the first segment. */
-- 
2.25.1

Thanks a lot!

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