On further digging i found that in producer_avformat.c:seek_video, if i
replace AVSEEK_FLAG_BACKWARD with AVSEEK_FLAG_ANY, then that "faulty" video
plays smoothly. It points to some issue with keyframes. What i was doing is
that i was generating series of PNG files using a
canvas-based-firefox-extended-animation script. Then i was stitching those
PNG files into a Theora video, using `ffmpeg -r 24 -qscale 31 -i %07d.png
output.ogv`. Most of the videos were running fine in melt, except one or
two. My idea was to put those small pieces of videos into kdenlive and make
an animated music video. So, as this or other specific video was not
working as expected, it was eating my brain alive :). But AVSEEK_FLAG_ANY
boosted some neurons and i finally realized that i need to put keyframe at
the begining of the video. Hence i tried `ffmpeg -r 24 -qscale 31 -i
%07d.png -g 1 output.ogv`, which puts keyframe in every frame, (although
using -g 1000 would work as well) and the resulted video worked smoothly on
melt without any code modification. I was even able to run that "faulty"
video properly after converting it using `ffmpeg -qscale 31 -i old.ogv -g 1
new.ogv`.
On Sat, Jun 16, 2012 at 6:45 AM, Dan Dennedy <[email protected]> wrote:
> On Thu, Jun 14, 2012 at 9:51 PM, Sujoy Roy <[email protected]> wrote:
> > I have uploaded the "specific" video using ftp. The filename is
> > beating_bars.ogv. While debugging through producer_avformat.c, i checked
> the
> > value of pkt.dts after av_read_frame being called in producer_get_image.
> And
> > found that its value is jumping from 0, 1 to directly to 169. And if i
> press
> > shift+h, then it goes back to the begining and plays perfectly ok, and
> value
> > of pkt.dts increases smoothly from 0,1,2,3, ...
> > After digging through this phenomena of shift+h, i found that when i am
> > pressing shft+h, it is calling reopen_video.
>
> There is something that is preventing libavformat from properly
> seeking within the first 20% or so of this file. When I play it in
> avplay and seek in the 5% to 20% range, then it too pauses for a while
> until time "catches up" to the stream. So, even if it were possible to
> overcome the problem playing from the beginning, if you set an in
> point somewhere before 169, then it will have a problem. If I force
> the clip to be non-seekable within
> producer_avformat.c:get_basic_info() then it does play fine, and that
> looks to be the only real workaround. The test for seek-ability passes
> on this clip, but it is not desirable to make the test more stringent.
> Usually, there are more false negatives than false positives. I could
> add a force_seekable property to the consumer so people can choose to
> workaround faulty clips for simple, sequential playback or transcode
> scenarios.
>
> > - Sujoy
> >
> >
> > On Fri, Jun 15, 2012 at 6:09 AM, Dan Dennedy <[email protected]> wrote:
> >>
> >> On Tue, Jun 12, 2012 at 11:36 AM, Sujoy Roy <[email protected]>
> wrote:
> >> > When i play a "specific" Theora video using melt, it freezes (sort
> of)
> >> > the
> >> > melt-screen upto first 190 frames, then it moves as expected. But it
> >> > plays
> >> > smoothly in ffmpeg or totem player, no freezing; i am on Fedora 16. I
> >> > have
> >> > downloaded the source code of melt. But there is no text containing
> >> > "theora" in those files. I guess the video decoding is being handled
> by
> >> > libavformat. Any tip about where to dive-in to find the cause of the
> >> > video
> >> > freezing?
> >>
> >> See src/modules/avformat/producer_avformat.c
> >>
> >> I am in the middle of a complete overhaul of the seek and sync in that
> >> piece of code. Likely your file will be affected as well as possibly
> >> any fix you come up with. If you upload it via anonymous ftp to
> >> dennedy.org, then I will take a look at it in the midst of checking my
> >> code changes.
> >>
> >> --
> >> +-DRD-+
> >
> >
> >
> >
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>
>
>
> --
> +-DRD-+
>
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