[vlc-devel] [PATCH] demux: hls: fix consistent live delay (#21614 WIP2)
Abdullah Alansari
ahimta at gmail.com
Wed Oct 2 16:06:44 CEST 2019
>From f9b9daf8d32134ca60c5af6c73be1a8fd49a73a5 Mon Sep 17 00:00:00 2001
From: Abdullah Alansari <ahimta at gmail.com>
Date: Mon, 30 Sep 2019 20:32:16 +0300
Subject: [PATCH] demux: hls: fix consistent live delay (#21614 WIP2)
The bug was first observed on
https://www.youtube.com/watch?v=WI86J46VRUc
This YouTube live-stream contains a wall-clock in the bottom-right
corner which makes it very convenient for testing.
Before this patch/fix, playback with VLC is 1minute+ behind the YouTube
website:sweat_smile: and after the patch, YouTube is the one
behind:smiley:.
This bug should manifest in all platforms in any YouTube live video.
The initial analysis of this bug showed that the reason for this delay
is that VLC plays the first video in the M38U file which can be 1minute+
before the current wall-clock time:sweat_smile:.
This was observed on http://www.tv.wataan.com/?video=show&show=104
where the delay was non-existent on Firefox and existent on VLC
:sweat_smile:.
On Firefox, the second-to-last video in the M3U8 was played while on
VLC the first video was played. And upon downloading both videos,
Firefox's downloaded has the correct wall-clock time while VLC's one
was 1minute+ behind:sweat_smile:.
And thus this patch does something similar to the Firefox observed
behavior above (which may just be from the website's own code).
I have almost the whole related RFC and the 6.3.3 sections is probably
the single most relevent:
https://tools.ietf.org/html/rfc8216#section-6.3.3
Specifically "the client SHOULD NOT choose a segment that
starts less than three target durations from the end of the
Playlist file."
This patch may possibly break non-HLS and not fix other adaptive-live
stuff (e.g: DASH), if they are already affected:sweat_smile:.
A list of tested samples that had the delay before this patch and don't
anymore:
1. https://www.youtube.com/watch?v=WI86J46VRUc
2. http://livecdnh3.tvanywhere.ae/hls/jadeed/03.m3u8
Related to https://trac.videolan.org/vlc/ticket/21614#attachments
---
modules/demux/adaptive/SegmentTracker.cpp | 8 ++++----
.../adaptive/playlist/BaseRepresentation.cpp | 5 ++++-
.../adaptive/playlist/BaseRepresentation.h | 5 ++++-
modules/demux/hls/playlist/Parser.cpp | 17 +++++++++++++----
modules/demux/hls/playlist/Parser.hpp | 6 ++++--
modules/demux/hls/playlist/Representation.cpp | 7 +++++--
modules/demux/hls/playlist/Representation.hpp | 5 ++++-
7 files changed, 38 insertions(+), 15 deletions(-)
diff --git a/modules/demux/adaptive/SegmentTracker.cpp
b/modules/demux/adaptive/SegmentTracker.cpp
index 583d977681..d54dcaf2a3 100644
--- a/modules/demux/adaptive/SegmentTracker.cpp
+++ b/modules/demux/adaptive/SegmentTracker.cpp
@@ -111,7 +111,7 @@ StreamFormat SegmentTracker::getCurrentFormat() const
{
/* Ensure ephemere content is updated/loaded */
if(rep->needsUpdate())
- (void) rep->runLocalUpdates(resources, 0, curNumber, false);
+ (void) rep->runLocalUpdates(resources, 0, curNumber, false,
true);
return rep->getStreamFormat();
}
return StreamFormat();
@@ -203,7 +203,7 @@ SegmentChunk * SegmentTracker::getNextChunk(bool
switch_allowed,
bool b_updated = false;
/* Ensure ephemere content is updated/loaded */
if(rep->needsUpdate())
- b_updated = rep->runLocalUpdates(resources, getPlaybackTime(),
curNumber, false);
+ b_updated = rep->runLocalUpdates(resources, getPlaybackTime(),
curNumber, false, false);
if(prevRep && !rep->consistentSegmentNumber())
{
@@ -310,7 +310,7 @@ bool SegmentTracker::setPositionByTime(vlc_tick_t time,
bool restarted, bool try
/* Stream might not have been loaded at all (HLS) or expired */
if(rep && rep->needsUpdate() &&
- !rep->runLocalUpdates(resources, time, curNumber, false))
+ !rep->runLocalUpdates(resources, time, curNumber, false, false))
{
msg_Err(rep->getAdaptationSet()->getPlaylist()->getVLCObject(),
"Failed to update Representation %s",
rep->getID().str().c_str());
@@ -391,7 +391,7 @@ void SegmentTracker::updateSelected()
{
if(curRepresentation && curRepresentation->needsUpdate())
{
- curRepresentation->runLocalUpdates(resources, getPlaybackTime(),
curNumber, true);
+ curRepresentation->runLocalUpdates(resources, getPlaybackTime(),
curNumber, true, false);
curRepresentation->scheduleNextUpdate(curNumber);
}
}
diff --git a/modules/demux/adaptive/playlist/BaseRepresentation.cpp
b/modules/demux/adaptive/playlist/BaseRepresentation.cpp
index 49b8cfcee0..17d33d6f24 100644
--- a/modules/demux/adaptive/playlist/BaseRepresentation.cpp
+++ b/modules/demux/adaptive/playlist/BaseRepresentation.cpp
@@ -94,7 +94,10 @@ bool BaseRepresentation::needsUpdate() const
}
bool BaseRepresentation::runLocalUpdates(SharedResources *,
- vlc_tick_t, uint64_t, bool)
+ vlc_tick_t,
+ uint64_t,
+ bool,
+ const bool isFirstPlaylist)
{
return false;
}
diff --git a/modules/demux/adaptive/playlist/BaseRepresentation.h
b/modules/demux/adaptive/playlist/BaseRepresentation.h
index 089ede1299..eeaff8fbdb 100644
--- a/modules/demux/adaptive/playlist/BaseRepresentation.h
+++ b/modules/demux/adaptive/playlist/BaseRepresentation.h
@@ -67,7 +67,10 @@ namespace adaptive
virtual vlc_tick_t getMinAheadTime (uint64_t)
const;
virtual bool needsUpdate () const;
virtual bool runLocalUpdates
(SharedResources *,
- vlc_tick_t,
uint64_t, bool);
+ vlc_tick_t,
+ uint64_t,
+ bool,
+ const bool
isFirstPlaylist);
virtual void scheduleNextUpdate (uint64_t);
virtual void debug (vlc_object_t
*,int = 0) const;
diff --git a/modules/demux/hls/playlist/Parser.cpp
b/modules/demux/hls/playlist/Parser.cpp
index fddcc9931a..bb72428bb7 100644
--- a/modules/demux/hls/playlist/Parser.cpp
+++ b/modules/demux/hls/playlist/Parser.cpp
@@ -144,7 +144,7 @@ void
M3U8Parser::createAndFillRepresentation(vlc_object_t *p_obj, BaseAdaptation
Representation *rep = createRepresentation(adaptSet, tag);
if(rep)
{
- parseSegments(p_obj, rep, tagslist);
+ parseSegments(p_obj, rep, tagslist, true);
if(rep->isLive())
{
/* avoid update playlist immediately */
@@ -155,7 +155,9 @@ void
M3U8Parser::createAndFillRepresentation(vlc_object_t *p_obj, BaseAdaptation
}
}
-bool M3U8Parser::appendSegmentsFromPlaylistURI(vlc_object_t *p_obj,
Representation *rep)
+bool M3U8Parser::appendSegmentsFromPlaylistURI(vlc_object_t *p_obj,
+ Representation *rep,
+ const bool isFirstPlaylist)
{
block_t *p_block = Retrieve::HTTP(p_obj, resources->getAuthStorage(),
rep->getPlaylistUrl().toString());
@@ -167,7 +169,7 @@ bool
M3U8Parser::appendSegmentsFromPlaylistURI(vlc_object_t *p_obj, Representati
std::list<Tag *> tagslist = parseEntries(substream);
vlc_stream_Delete(substream);
- parseSegments(p_obj, rep, tagslist);
+ parseSegments(p_obj, rep, tagslist, isFirstPlaylist);
releaseTagsList(tagslist);
}
@@ -212,7 +214,10 @@ static bool parseEncryption(const AttributesTag
*keytag, const Url &playlistUrl,
}
}
-void M3U8Parser::parseSegments(vlc_object_t *, Representation *rep, const
std::list<Tag *> &tagslist)
+void M3U8Parser::parseSegments(vlc_object_t *,
+ Representation *rep,
+ const std::list<Tag *> &tagslist,
+ const bool isFirstPlaylist)
{
SegmentList *segmentList = new (std::nothrow) SegmentList(rep);
@@ -365,6 +370,10 @@ void M3U8Parser::parseSegments(vlc_object_t *,
Representation *rep, const std::l
if(rep->isLive())
{
+ if (isFirstPlaylist) {
+ segmentList->pruneBySegmentNumber(sequenceNumber - 1);
+ }
+
rep->getPlaylist()->duration.Set(0);
}
else if(totalduration > rep->getPlaylist()->duration.Get())
diff --git a/modules/demux/hls/playlist/Parser.hpp
b/modules/demux/hls/playlist/Parser.hpp
index fc0ac6314f..824bfef360 100644
--- a/modules/demux/hls/playlist/Parser.hpp
+++ b/modules/demux/hls/playlist/Parser.hpp
@@ -58,13 +58,15 @@ namespace hls
virtual ~M3U8Parser ();
M3U8 * parse (vlc_object_t *p_obj, stream_t
*p_stream, const std::string &);
- bool appendSegmentsFromPlaylistURI(vlc_object_t *,
Representation *);
+ bool appendSegmentsFromPlaylistURI(vlc_object_t *,
+ Representation *,
+ const bool
isFirstPlaylist);
private:
Representation * createRepresentation(BaseAdaptationSet *,
const AttributesTag *);
void createAndFillRepresentation(vlc_object_t *,
BaseAdaptationSet *,
const AttributesTag *,
const std::list<Tag *>&);
- void parseSegments(vlc_object_t *, Representation *, const
std::list<Tag *>&);
+ void parseSegments(vlc_object_t *, Representation *, const
std::list<Tag *>&, const bool);
std::list<Tag *> parseEntries(stream_t *);
adaptive::SharedResources *resources;
};
diff --git a/modules/demux/hls/playlist/Representation.cpp
b/modules/demux/hls/playlist/Representation.cpp
index 6be82ac9e8..b2cce3f376 100644
--- a/modules/demux/hls/playlist/Representation.cpp
+++ b/modules/demux/hls/playlist/Representation.cpp
@@ -137,14 +137,17 @@ bool Representation::needsUpdate() const
}
bool Representation::runLocalUpdates(SharedResources *res,
- vlc_tick_t, uint64_t, bool)
+ vlc_tick_t,
+ uint64_t,
+ bool,
+ const bool isFirstPlaylist)
{
const time_t now = time(NULL);
AbstractPlaylist *playlist = getPlaylist();
if(!b_loaded || (isLive() && nextUpdateTime < now))
{
M3U8Parser parser(res);
- parser.appendSegmentsFromPlaylistURI(playlist->getVLCObject(),
this);
+ parser.appendSegmentsFromPlaylistURI(playlist->getVLCObject(),
this, isFirstPlaylist);
b_loaded = true;
return true;
diff --git a/modules/demux/hls/playlist/Representation.hpp
b/modules/demux/hls/playlist/Representation.hpp
index 444b2a1481..13f9068881 100644
--- a/modules/demux/hls/playlist/Representation.hpp
+++ b/modules/demux/hls/playlist/Representation.hpp
@@ -51,7 +51,10 @@ namespace hls
virtual bool needsUpdate() const; /* reimpl */
virtual void debug(vlc_object_t *, int) const; /* reimpl
*/
virtual bool runLocalUpdates(SharedResources *,
- vlc_tick_t, uint64_t, bool);
/* reimpl */
+ vlc_tick_t,
+ uint64_t,
+ bool,
+ const bool isFirstPlaylist);
/* reimpl */
virtual uint64_t translateSegmentNumber(uint64_t, const
SegmentInformation *) const; /* reimpl */
private:
--
2.20.1
--
Abdullah Alansari,
LinkedIn: https://linkedin.com/in/ahimta
GitHub: https://github.com/Ahimta
Twitter: https://twitter.com/Ahymta
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