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

[Li Kai <wolfleekay@gmail.com>]

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OK,  I got it.

Thanks a lot.


在 2022/6/27 上午10:23, Steven Liu 写道:
> Li Kai <wolfleekay@gmail.com> 于2022年6月25日周六 22:15写道：
>> OK, I add the option description in doc/demuxers.texi.
>>
>> About invalid EXT-X-START value, it's not played on Safari.
>> So I make it error to handle.
>>
>> You opinion, it's better way. The latest patch fix it.
>>
>>
>>
> @@ -741,6 +744,7 @@ 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 +893,20 @@ static int parse_playlist(HLSContext *c, const char *url,
>                   cur_init_section->key = NULL;
>               }
>
> +        } else if (av_strstart(line, "#EXT-X-START:", &ptr)) {
> Can the "const char *p;" move to here? And maybe make a clarify name
> will better i think, e.g. const char *time_offset_value?
>
> +            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 {
> +                av_log(c->ctx, AV_LOG_WARNING, "#EXT-X-START value is"
> +                                                "invalid, it will be ignored");
> +                continue;
> +            }
>           } else if (av_strstart(line, "#EXT-X-ENDLIST", &ptr)) {
>               if (pls)
>                   pls->finished = 1;
>
>
>
> Thanks
> Steven

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From 9c812414bc21030182fda00e702ea6433c920c9d Mon Sep 17 00:00:00 2001
From: Li Kai <wolfleekay@gmail.com>
Date: Thu, 23 Jun 2022 00:55:38 +0800
Subject: [PATCH v4] avformat/hls: add #EXT-X-START tag support by
 prefer_x_start opt

Signed-off-by: Li Kai <wolfleekay@gmail.com>
---
 doc/demuxers.texi |  3 +++
 libavformat/hls.c | 60 +++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/doc/demuxers.texi b/doc/demuxers.texi
index c95a9ae594..2b6dd86c2a 100644
--- a/doc/demuxers.texi
+++ b/doc/demuxers.texi
@@ -373,6 +373,9 @@ It accepts the following options:
 @item live_start_index
 segment index to start live streams at (negative values are from the end).
 
+@item prefer_x_start
+prefer to use #EXT-X-START if it's in playlist instead of live_start_index.
+
 @item allowed_extensions
 ',' separated list of file extensions that hls is allowed to access.
 
diff --git a/libavformat/hls.c b/libavformat/hls.c
index b736f093a9..8ea4ff4671 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;
@@ -211,6 +213,7 @@ typedef struct HLSContext {
     int64_t cur_seq_no;
     int m3u8_hold_counters;
     int live_start_index;
+    int prefer_x_start;
     int first_packet;
     int64_t first_timestamp;
     int64_t cur_timestamp;
@@ -889,6 +892,21 @@ 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;
+            }
+            const char *time_offset_value;
+            if (av_strstart(ptr, "TIME-OFFSET=", &time_offset_value)) {
+                float offset = strtof(time_offset_value, NULL);
+                pls->start_time_offset = offset * AV_TIME_BASE;
+                pls->time_offset_flag = 1;
+            } else {
+                av_log(c->ctx, AV_LOG_WARNING, "#EXT-X-START value is"
+                                                "invalid, it will be ignored");
+                continue;
+            }
         } else if (av_strstart(line, "#EXT-X-ENDLIST", &ptr)) {
             if (pls)
                 pls->finished = 1;
@@ -1722,9 +1740,45 @@ 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 && c->prefer_x_start) {
+            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. */
@@ -2476,6 +2530,8 @@ static int hls_probe(const AVProbeData *p)
 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},
+    {"prefer_x_start", "prefer to use #EXT-X-START if it's in playlist instead of live_start_index",
+        OFFSET(prefer_x_start), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, 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)


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