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Charles Mason | 12 Jun 18:34

FFMEG2Threora Bug

Today I was transcoding a video using the latest release of
ffmpeg2theora and noticed some strange artifacts in the output video.
In areas which are very white small black marks appear. I was
transcoding the blender open movie "Big Buck Bunny" and its very
noticeable on the credits in particular. The source video was their
official 1080p .ogg download.

I have uploaded a screen grab of the problem. It appears worst in the
credits but if you look closely it is in the entire video.

http://img365.imageshack.us/my.php?image=ffmpeg2theorabugzs7.png

I have included the ffmpeg2theora command I was running.

ffmpeg2theora.exe big_buck_bunny_1080p_stereo.ogg -V 5000 -x 1280 -y
720 -A 192 -c 2 -H 44100 --no-skeleton -o "Bug Buck Bunny.ogv"

I haven't noticed this on previous versions of ffmpeg2theora although
I haven't tried this source material with it. I have tried playing it
in VLC as well as the Theora playing app I am currently working on.
The latter uses the latest libtheora release with the new decoder api.
Both show the same output so I assume its a bug in the encoder.

Has any one else come across this problem?

Charlie M
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"Ivo Emanuel =?iso-8859-1?q?Gon=E7alves=22?= | 12 Jun 22:09

Re: FFMEG2Threora Bug

 j has made several changes since 0.21.  Can you compile from SVN and
re-test?  If it's still there we have a... situation.

-Ivo
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Charles Mason | 13 Jun 10:56

Re: FFMEG2Threora Bug

On Thu, Jun 12, 2008 at 9:09 PM, Ivo Emanuel Gonçalves
<justivo <at> gmail.com> wrote:
>  j has made several changes since 0.21.  Can you compile from SVN and
> re-test?  If it's still there we have a... situation.

I will have a ago, although I havn't compiled ffmpeg2theora from
source as yet so it may me a while.

If anyone has a recent windows build of the ffmpeg2theora SVN handy it
would save me sometime :)

In the mean time I shall attempt to compile it my self.

Charlie M
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Conrad Parker | 13 Jun 01:05
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Re: FFMEG2Threora Bug

2008/6/13 Charles Mason <charlie.mas <at> gmail.com>:
> Today I was transcoding a video using the latest release of
> ffmpeg2theora and noticed some strange artifacts in the output video.
> In areas which are very white small black marks appear. I was
> transcoding the blender open movie "Big Buck Bunny" and its very
> noticeable on the credits in particular. The source video was their
> official 1080p .ogg download.

You're transcoding from compressed Ogg Theora to compressed Ogg Theora?

Conrad.
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"Ivo Emanuel =?iso-8859-1?q?Gon=E7alves=22?= | 13 Jun 05:50

Re: FFMEG2Threora Bug

On 6/13/08, Conrad Parker <conrad <at> metadecks.org> wrote:
> You're transcoding from compressed Ogg Theora to compressed Ogg Theora?

That does work in ffmpeg2theora.  Weird glitches that are not result
of the compression should not appear, though.  If they are there, then
it's a bug.

Actually, direct transcoding is useful in certain situations, like say
your original source is Theora and you want to lower the file-size to
place it in your web site, so you end up doing it.  A similar feature
for oggenc has been requested so many times, it's not even funny, so
it's good that ffmpeg2theora can do it.

-Ivo
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Charles Mason | 13 Jun 10:50

Re: FFMEG2Threora Bug

On Fri, Jun 13, 2008 at 12:05 AM, Conrad Parker <conrad <at> metadecks.org> wrote:
> 2008/6/13 Charles Mason <charlie.mas <at> gmail.com>:
>> Today I was transcoding a video using the latest release of
>> ffmpeg2theora and noticed some strange artifacts in the output video.
>> In areas which are very white small black marks appear. I was
>> transcoding the blender open movie "Big Buck Bunny" and its very
>> noticeable on the credits in particular. The source video was their
>> official 1080p .ogg download.
>
> You're transcoding from compressed Ogg Theora to compressed Ogg Theora?

Yeah, on the face of it sounds crazy I know. However may app needs to
be able to join a number of separate ogg files into a single logical
stream. Because the setup headers are missing from all but the first
stream, everything about the streams must be identical. For various
reasons I can't simply have multiple ogg streams in the output. Not
least the fact that most current Theora players will only play the
first stream, despite the spec allowing an unlimited number.

So for Theora that means the frame rate, target bit rate, and the
resolution all must be identical. For Vorbis streams the sample rate,
target bit rate and total channels all must be identical. Also because
each encoder implementation is able to produce different setup packets
(to allow improvements in the encoder) they all need to be encoded
with the same implementation of the encoder and likley the same
version.

On the face of it this might seem like a lot of restrictions but for
my particular needs its fine. To make this process work the app has to
adjust the granualpos timestamps on each Theora / Vorbis packet. It
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