[FFmpeg-trac] #6915(avformat:open): DASH audio segments duration doesn't match exactly with video segments duration.
FFmpeg
trac at avcodec.org
Thu Dec 21 17:33:50 EET 2017
#6915: DASH audio segments duration doesn't match exactly with video segments
duration.
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Reporter: beloko | Owner: stevenliu
Type: defect | Status: open
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:22 stevenliu]:
> Replying to [comment:21 j_karthic]:
> > Replying to [comment:19 stevenliu]:
> > > Replying to [comment:18 stevenliu]:
> > > > Replying to [comment:17 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.
> > > >
> > > > what will happen when just round the target duration ？i think the
EXTINF will large than target duration
> > > round up it is no problem, but round down will have different result
for users understand,This is why implement an api to process it for round
up.
> > Well as long as it follows the spec, we need not worry. If the players
were implemented as per the HLS spec then they should handle this case
correctly.
>
> I will try to fix this problem
Oh! I am glad that we are on the same page. Thanks for your understanding.
Regarding the fix, I think fixing the target duration is good enough. For
that I have already sent a patch. http://ffmpeg.org/pipermail/ffmpeg-
devel/2017-December/222745.html
It is theoretically not possible to get audio duration to exactly 4.00000
seconds. Because an AAC frame size is 1024 which is not a divisor of
4*48000 or 4*44100. So the audio segment can't be cut at exact 4.00000
seconds. Even the HLS spec is fine with that. In section 6.2.4. Providing
Variant Streams, it mentions that the target duration of all variants to
be same. No explicit mention for the EXTINF duration indirectly means that
those durations need not be exactly same(as it is not possible
theoretically).
{{{
Each Media Playlist in each Variant Stream MUST have the same
target duration. The only exceptions are SUBTITLES Renditions and
Media Playlists containing an EXT-X-I-FRAMES-ONLY tag, which MAY
have different target durations if they have an EXT-X-PLAYLIST-
TYPE of VOD.
}}}
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--
Ticket URL: <https://trac.ffmpeg.org/ticket/6915#comment:24>
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