On Fri, Dec 08, 2017 at 01:09:50AM -0300, James Almer wrote:
> On 12/8/2017 12:26 AM, wm4 wrote:
> > On Thu, 7 Dec 2017 23:23:51 +0100
> > Michael Niedermayer <mich...@niedermayer.cc> wrote:
> >
> >> On Tue, Nov 21, 2017 at 07:58:18PM +0100, Michael Niedermayer wrote:
> >>> On Sat, Nov 18, 2017 at 09:11:17PM +0100, Michael Niedermayer wrote:
> >>>> On Sat, Nov 18, 2017 at 09:50:33AM +0100, Hendrik Leppkes wrote:
> >>>>> On Sat, Nov 18, 2017 at 3:05 AM, Michael Niedermayer
> >>>>> <mich...@niedermayer.cc> wrote:
> >>>>>> On Fri, Nov 17, 2017 at 09:55:47AM +0100, Hendrik Leppkes wrote:
> >>>>>>> On Fri, Nov 17, 2017 at 5:00 AM, Michael Niedermayer
> >>>>>>> <mich...@niedermayer.cc> wrote:
> >>>>>>>> On Thu, Nov 16, 2017 at 01:51:34PM +0100, Carl Eugen Hoyos wrote:
> >>>>>>>>> 2017-11-16 13:44 GMT+01:00 Michael Niedermayer <mich...@niedermayer.cc>:
> >>>>>>>>>> On Thu, Nov 16, 2017 at 01:04:27AM +0100, Carl Eugen Hoyos wrote:
> >>>>>>>>>>> 2017-11-15 13:34 GMT+01:00 Michael Niedermayer <mich...@niedermayer.cc>:
> >>>>>>>>>>>> Hi all
> >>>>>>>>>>>>
> >>>>>>>>>>>> I intend to make 3.4.1 very soon
> >>>>>>>>>>>
> >>>>>>>>>>> Shouldn't we first decide on how to proceed with #6775?
> >>>>>>>>>>
> >>>>>>>>>> This would be ideal.
> >>>>>>>>>>
> >>>>>>>>>> IIUC this is a regression from bddb2343b6e594e312dadb5d21b408702929ae04
> >>>>>>>>>
> >>>>>>>>> This was confirmed by more than one developer, yes.
> >>>>>>>>>
> >>>>>>>>>> I see a patch that is said to improve 6775, can that be applied and
> >>>>>>>>>> would that resolve this ?
> >>>>>>>>>
> >>>>>>>>> Iiuc, it would not completely resolve the issue, see:
> >>>>>>>>> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=881536
> >>>>>>>>>
> >>>>>>>>>> If so why was it not applied yet ?
> >>>>>>>>>
> >>>>>>>>> The patch did not get support here, see:
> >>>>>>>>> [FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after
EOF
> >>>>>>>>> in compat_decode
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Is someone working on fixing this better than with the available
patch ?
> >>>>>>>>
> >>>>>>>
> >>>>>>> I don't even agree this needs fixing. Those projects use the API wrong.
> >>>>>>
> >>>>>> Had we documented the correct/wrong use precissely in the past when
> >>>>>> these wrong uses where written ?
> >>>>>>
> >>>>>> Because if it was documented then few should have made the mistake.
> >>>>>> But it seems this affects multiple projects, so i wonder if our API
> >>>>>> really excluded the use
> >>>>>>
> >>>>>
> >>>>> Apparently not well enough, but I also don't even understand why you
> >>>>> would *want* to drain in the middle of decoding.
> >>>>>
> >>>>> The only mention of sending NULL/0 packets (in 3.0 docs, before the
> >>>>> new API was introduced) do include the "at the end", however.
> >>>>>
> >>>>> From CODEC_CAP_DELAY:
> >>>>> * Decoders:
> >>>>> * The decoder has a non-zero delay and needs to be fed with
avpkt->data=NULL,
> >>>>> * avpkt->size=0 at the end to get the delayed data until the decoder
no longer
> >>>>> * returns frames.
> >>>>>
> >>>>> From avcodec_decode_video2
> >>>>> * @note Codecs which have the AV_CODEC_CAP_DELAY capability set have a
delay
> >>>>> * between input and output, these need to be fed with avpkt->data=NULL,
> >>>>> * avpkt->size=0 at the end to return the remaining frames.
> >>>>>
> >>>>> There is a few more mentions of the same concept, but as far as I can
> >>>>> see all include the key words "at the end".
> >>>>>
> >>>>
> >>>>> For the suggested patch, draining and flushing in the middle of a
> >>>>> bitstream is still going to result in problems, though, since it
> >>>>> removes all reference frames, for example.
> >>>>> The original behavior cannot really be stored, which was to just keep
> >>>>> feeding frames into the decoder after a drain without a flush.
> >>>>> However, some decoders actually crashed when you did this, so this was
> >>>>> a rather unsafe action to begin with (not an issue any longer, since
> >>>>> this pattern is now blocked).
> >>>>
> >>>> Did the previous code really work if the frame after a flush was not a
> >>>> new keyframe or there was some use of previous references ?
> >>>
> >>> ping
> >>>
> >>> so what is the status of this?
> >>>
> >>> Ticket 6775 is still open, neither a workaround was applied nor was
> >>> it closed as invalid. Only one workaround was proposed which was
> >>> claimed to be worse than the code before.
> >>> It seems the discussion died down.
> >>> If theres no activity on this in the next days then i intend to make
> >>> the release with whats in release/3.4 at the time. I dont think
> >>> blind waiting will do any good, id rather release early and often ...
> >>>
> >>> Also if someone wants to write some release notes about this issue,
> >>> that is IMO a good idea ...
> >>
> >> So this code is completely unmaintained ?
> >> Noone cares about pushing a workaround ?
> >> Noone cares about closing the ticket as wont fix ?
> >> Noone cares about explaining why neither should be done ?
> >>
> >> I intend to make the release tomorrow or as soon as i have time, we
> >> have waited too long already. I can of course wait more if people want
> >> but then please have a plan on resolving the issue that the release is
> >> delayed for
> >
> > I didn't read all of this, but it's probably due to the API user
> > passing as null packet, which indeed signals EOF. What happens if you
> > send more packets after sending EOF has always been undefined behavior,
> > and some audio decoders could crash if you did that. (It's fine if
> > you flush the decoder, of course.) I think I brought it up in the past
> > (and nobody cared), so I added explicit workarounds to my own API usage
> > code to avoid crashes. Why are you making so much noise around it now?
>
> When the old decode API was turned into a wrapper for the new, some
> applications using said API this way started to experience
> issues/crashes that did not happen before. So basically, a change of
> behavior which, as you put it, was apparently undefined.
>
> Some argue it should not crash if it didn't before, others argue that it
> was never meant to be used this way. What Michael wants to know in order
> to release 3.4.1 is, what should be done? Should it be addressed, or
> left as is? If the former, do we apply the patch someone proposed in
> another thread, or something else? If the latter, then the ticket should
> be closed and the discussion ends there.
yes
also to add to this, 6775 is set to the highest priority (critical)
