[theora] Google Puts Weight Behind Theora
claus at claushoefele.com
Sat Apr 10 17:02:19 PDT 2010
That's great news. I especially like the part where Theorarm became
available under BSD and will be merged back into the main Xiph branch.
Looking forward to giving this library a go on iPhone.
2010/4/11 <theora-request at xiph.org>:
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> Today's Topics:
> 1. Google Puts Weight Behind Theora (Jason Self)
> 2. Re: encoding raw file (.yuv) using ffmpeg2theora (Gregory Maxwell)
> Message: 1
> Date: Fri, 09 Apr 2010 16:38:02 -0700 (PDT)
> From: "Jason Self" <jason at bluehome.net>
> Subject: [theora] Google Puts Weight Behind Theora
> To: theora at xiph.org
> Message-ID: <1270856282.28176 at bluehome.net>
> Content-Type: text/plain; charset="iso-8859-1"
> "... we need a baseline to work from - one standard format that (if all else
> fails) everything can fall back to. This doesn?t need to be the most complex
> format, or the most advertised format, or even the format with the most companies
> involved in its creation. All it needs to do is to be available, everywhere. The
> codec in the frame for this is Ogg Theora..."
> Message: 2
> Date: Sat, 10 Apr 2010 13:40:02 -0400
> From: Gregory Maxwell <gmaxwell at gmail.com>
> Subject: Re: [theora] encoding raw file (.yuv) using ffmpeg2theora
> To: savo at graphics.cs.msu.ru
> Cc: theora at xiph.org
> <p2ke692861c1004101040l84a015f7s8fddf0dc4166ed8d at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
> On Wed, Mar 17, 2010 at 12:10 PM, Alexander Parshin
> <savo at graphics.cs.msu.ru> wrote:
>> I'm trying to use ffmpeg2theora to encode raw (.yuv) files in I420
>> format (just frames, no headers at all), but failed to find
>> corresponding input format. Is there any documentation of supported
>> formats for ffmpeg2theora?
>> Or maybe there is another command-line tool for Windows to encode raw
>> video using Theora algorithm?
>> Thank you for help!
> You might find the following notes from our wiki helpful:
> ==Speed and quality==
> If you need really high speed and don't care if the bitrate is
> enormous (or the quality is really poor) you can use speed level 2.
> The purpose it was created for was from keeping video encoding from
> falling behind on the OLPC. A live encoder could temporarily switch
> to it to catch up, for example. But because it disables half of the
> format, the quality is really terribly except at very high bitrates.
> ==Rate control and quality==
> Another piece of advice is that by default one pass rate control
> imposes a buffering constraint: It does not allow the instantaneous
> bitrate to go above what could be satisfied by a small buffer. This
> is important for real time streaming, but it can be absolutely brutal
> on the quality. Two-pass does not, because other video formats used
> in infinite latency applications don't do any buffer constraint. You
> can use the buf-delay knob to control the amount of buffer constraint.
> ==Encoder_example peculiarities==
> Theora uses the JPEG chroma siting. Encoder_example will automatically
> resample non-jpeg sited input to the JPEG positions. This can be
> surprising if you don't know that it does it.
> Like many other formats Theora must encode an area that is a multiple
> of 16x16 pixels. If you have a video that isn't a multiple of that
> size the tools round up then leave a note in the format to tell the
> decoder to crop down. All tools do this.
> Theora has an offset header that allows the cropped header to be
> some-place other than in one extreme corner of the video. A few
> decoder tools (e.g. mplayer, ffmpeg) have ignored this offset
> parameter and sometimes the crop parameter, causing offset videos to
> come out slightly shifted.
> Encoder_example always centers the video. This makes people more
> likely to notice offset-broken decoders. It does, unfortunately, seem
> to reduce quality for some clips because of how the invisible area can
> interact with motion prediction.
> Regardless of the encoder used you're best off it you can choose sizes
> which are a multiple of 16x16.
> ==The most current Theora encoder==
> You also might want to try out the current encoder rather than the
> older stuff. It's available from SVN at
> http://svn.xiph.org/experimental/derf/theora-ptalarbvorm/ and can
> also be used with ffmpeg2theora.
> Compared to 1.1, the new encoder produces nicely improved visual
> results though watch out because the visual optimizations are not good
> for PSNR (though they do enormously improve SSIM).
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> End of theora Digest, Vol 71, Issue 6
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