[vlc-devel] [PATCH] Subtitle delay : fixed sync problem that breaks audio under linux
pthomet at gmail.com
Mon Jun 2 10:41:40 CEST 2014
Actually, you may have to shift the subtitles when they comes from another
source, under the form of a subtitle file that was prepared for another
version of the video you are looking at. I never needed to do it on a DVD.
On Mon, Jun 2, 2014 at 8:09 AM, Julian Scheel <julian at jusst.de> wrote:
> On 02.06.2014 00:28, Pascal Thomet wrote:
>> Thanks for taking the time to answer. I will make some test with a DVD
>> that includes subtitles. Any ideas about other format that should be
>> tested as well ?
> You should take DVB into account. Actually I had DVB in mind with my
> previous mail.
> My impression however is that concerning format like DVD where the
>> subtitles are muxed into the stream, there should really never be any
>> need to delay the subtitles : if the subtitles were out of sync on a
>> dvd, it would means that the DVD is garbage anyway.
> For DVB subtitles I can think of a case where you'd want to resync: On
> live events are delayed some seconds as they are written on the fly. So it
> might be worth shifting them if one prefers proper subtitles over fewer
> overall delay.
> But this is just my 2 cents, in fact I don't use subtitles at all
> personally. So no clue why and when people shift them :)
> Concerning the tooltip I will make it a separate patch.
>> I might take me a few days before I can post a corrected set of patches.
>> Pascal Thomet
>> On Sun, Jun 1, 2014 at 10:47 AM, Julian Scheel <julian at jusst.de
>> <mailto:julian at jusst.de>> wrote:
>> Am 30/05/14 22:04, schrieb Pascal Thomet:
>> This is a follow-up to a patch I made last year
>> When developping it I stumbled upon a prexisting bug that I could
>> not correct at that time.
>> I now propose a correction for this bug, as well as tooltip that
>> explain the use of the hotkeys introduced by
>> tests passed / compile and runs correctly in debug & release modes
>> under linux & OSX
>> 1) Bug correction info :
>> * * * * * * * * *
>> Bug reproduction step : *under linux* (will not happen under OSX)
>> - launch a video that has a subtitle,
>> - press Shift-H ("bookmark audio time"),
>> - wait 5 seconds
>> - press Shift-J ("bookmark subtitle time")
>> - press Shift-K ("sync bookmarks")
>> ==> the audio is broken...
>> (AFAIK this bug seems not to be mentioned on trac.videolan.org
>> The subtitle delay ("spu-delay") was previously implemented by
>> i) setting a variable spu-delay
>> (var_SetTime(... , "spu-delay", ... ))
>> ii) this change raised a callback that finaly lead to calling
>> The reason UpdatePtsDelay() was called is that the subtitle delay
>> was programed the same way as the audio delay (for which it is
>> to wait until the audio is actually demuxed)
>> *However* the situation for subtitles is quite different, as
>> they are all in memory
>> (no need to wait until they are demuxed !)
>> This really depends on the subtitle source. In case of dvb subtitles
>> in mpeg ts they are not all in memory but come muxed into the stream.
>> The code is now more simple (and the bug is fixed !) :
>> - no more delay calculations inside hotkeys.c, everything is
>> inside subtitle.c through callbacks
>> - inside subtitle.c :
>> * adjust_subtitle_time() receives a subtitle timestamp as
>> input and returns
>> that timestamp corrected by spu-delay
>> * set_current_subtitle_by_time() is called when spu-delay
>> is changed
>> 2) Tooltip
>> * * * *
>> imho this should be split into a separate patch.
>> This adds a tooltip in the "Track Synchronization" window
>> on the "subtitle track sycnhronization" label and widget.
>> It explains better the use of the subtitle sync hotkeys
>> (Shift H/J/K)
>> Also tested under Linux & OSX.
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