[FFmpeg-trac] #6915(avformat:new): DASH audio segments duration doesn't match exactly with video segments duration.
FFmpeg
trac at avcodec.org
Thu Dec 21 15:06:55 EET 2017
#6915: DASH audio segments duration doesn't match exactly with video segments
duration.
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Reporter: beloko | Owner:
Type: defect | Status: new
Priority: normal | Component: avformat
Version: git-master | Resolution:
Keywords: | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
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Comment (by j_karthic):
Replying to [comment:16 stevenliu]:
> Replying to [comment:15 j_karthic]:
> > Replying to [comment:14 stevenliu]:
> > > Replying to [comment:13 j_karthic]:
> > > > Replying to [comment:12 stevenliu]:
> > > > > Replying to [comment:11 j_karthic]:
> > > > > > Replying to [comment:10 stevenliu]:
> > > > > > > Replying to [comment:9 j_karthic]:
> > > > > > > > Replying to [comment:8 stevenliu]:
> > > > > > > > > Replying to [comment:7 j_karthic]:
> > > > > > > > > > Well, if we round the target duration to '''nearest
integer''' as per the spec, part of the problem is resolved. Right now we
are '''ceiling to the upper integer''' which is not according to HLS
specifications.
> > > > > > > > > >
> > > > > > > > > > {{{
> > > > > > > > > > 4.3.3.1. EXT-X-TARGETDURATION
> > > > > > > > > >
> > > > > > > > > > The EXT-X-TARGETDURATION tag specifies the maximum
Media Segment
> > > > > > > > > > duration. The EXTINF duration of each Media
Segment in the Playlist
> > > > > > > > > > file, when rounded to the nearest integer, MUST be
less than or equal
> > > > > > > > > > to the target duration; longer segments can trigger
playback stalls
> > > > > > > > > > or other errors. It applies to the entire Playlist
file. Its format
> > > > > > > > > > is:
> > > > > > > > > >
> > > > > > > > > > #EXT-X-TARGETDURATION:<s>
> > > > > > > > > >
> > > > > > > > > > where s is a decimal-integer indicating the target
duration in
> > > > > > > > > > seconds. The EXT-X-TARGETDURATION tag is REQUIRED.
> > > > > > > > > >
> > > > > > > > > > }}}
> > > > > > > > > >
> > > > > > > > > > So as per the spec, the EXT-X-TARGETDURATION should
rounded to 4 instead of 5.
> > > > > > > > > >
> > > > > > > > > > But when I submitted a patch for fixing such an issue
in hlsenc, it was rejected by Steven. See thread
http://ffmpeg.org/pipermail/ffmpeg-devel/2017-September/215630.html more
details. During that time, I was not able to provide a concrete example
with mediastreamvalidator like @beloko has done now. But I thought the
spec was very clear about it without any room for confusion.
> > > > > > > > > >
> > > > > > > > > > @stevenliu
> > > > > > > > > > If you have a change of mind after seeing these
results, please let me know. Maybe I will send a new patch which fixes the
target duration in dashenc, and we can take forward our discussions there.
> > > > > > > > >
> > > > > > > > > The spec said "EXT-X-TARGETDURATION must > EXTINF", we
have talk and you have sent twice patch about it. you can see the spec
said "MUST be less than or equal to the target duration.", attention the
MUST, MUST, MUST, we should don't care the tool, we should care the spec.
If the tool different with the spec, that maybe apple's mistake, you
should push apple.
> > > > > > > > I think you missing the important line "'''when rounded to
the nearest integer'''" in the spec. I am also only talking about the
spec. This is just a pure argument, about interpreting that English line.
This is where I feel some other people in the ffmpeg community should also
pitch in moderate a discussion, rather than leaving it as "'''Maintainer
is always right'''".
> > > > > > > '''Maintainer''' not always right, but can you give me the
mean '''MUST be less than or equal to the target duration''' how should i
understand it?
> > > > > > "'''when rounded to the nearest integer, MUST be less than or
equal to the target duration'''" is in one sentence. That should be read
in conjunction with the phrase "when rounded to the nearest integer". It
means after rounding duration to the nearest integer, it MUST be less than
or equal to the target duration.
> > > > > how should i understand the '''target duration'''?
> > > > > do you mean, when the '''EXTINF''' is '''1.080000''', the
'''EXT-X-TARGETDURATION''' should equal to '''1''' ?
> > > > As per the spec, Yes.
> > > I coding for hls from VERSION 1, from old VERSION,
https://tools.ietf.org/html/draft-pantos-http-live-streaming-03
> > > about the EXT-X-TARGETDURATION said:
> > >
> > >
> > > {{{
> > > 3.2.1. EXT-X-TARGETDURATION
> > >
> > > The EXT-X-TARGETDURATION tag specifies the maximum media file
> > > duration. The EXTINF duration of each media file in the Playlist
> > > file MUST be less than or equal to the target duration. This tag
> > > MUST appear once in the Playlist file. Its format is:
> > >
> > > #EXT-X-TARGETDURATION:<s>
> > >
> > > where s is an integer indicating the target duration in seconds.
> > > }}}
> > >
> > > so, i always understand it to EXT-X-TARGETDURATION must large than
EXTINF,
> > > I have sent a Email to hls team of apple for check this description,
maybe there have some misunderstanding words here.
> > In that version of HLS, floating point segment duration was not
supported. The segment durations were already integers. Hence there is no
question of rounding, when target duration was being defined.
> > But later when the floating point segment duration was supported in
HLS, the definition for target duration was modified to specify "when
rounded to nearest integer" to handle floating point segment durations.
>
> Sorry for my poor English, but i think the '''when rounded to the
nearest integer''' is description for '''The EXTINF duration of each Media
Segment in the Playlist file,''', because the they in one sentence, and
the next sentence said '''longer segments can trigger playback stalls or
other errors''', so, the reason to make there have no '''longer segments
can trigger playback stalls or other errors''' error, not use lrint.
> When EXTINF is 1.080000, set the EXT-X-TARGETDURATION to 2.
Well, let me explain that entire sentence as a pseudo code.
{{{
The EXTINF duration of each Media Segment in the Playlist
file, when rounded to the nearest integer, MUST be less than or equal
to the target duration; longer segments can trigger playback stalls
or other errors.
}}}
{{{
for each media segment {
if (round(EXTINF_duration) <= target_duration) { //when rounded to the
nearest integer, MUST be less than or equal to the target duration
Everything is fine here
} else { // longer segments ...
//Basically when (round(EXTINF_duration) > target_duration)
playback stalls or other errors can be triggered;
}
}
}}}
'''longer segments can trigger playback stalls or other errors''', is
still part of the same sentence. This means longer after rounding to the
nearest integer.
> > >
> > >
> > > > >
> > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
--
Ticket URL: <https://trac.ffmpeg.org/ticket/6915#comment:17>
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