[MPlayer-users] Mencoder fails: Cannot initialize video driver

[Da Rock]

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> Date: Wed, 23 Jan 2008 21:11:35 -0500
> To: mplayer-users at mplayerhq.hu
> From: dalias at aerifal.cx
> Subject: Re: [MPlayer-users] Mencoder fails: Cannot initialize video driver
> 
> On Thu, Jan 24, 2008 at 01:44:36AM +0000, Da Rock wrote:
>> 
>> Sorry, what exactly does the keyint do? I thought it was simply the
>> fps output based on the context it was put in. What is the bitrate
>> overhead you're talking about too (while we're on this subject)?
> 
> Please don't top-post.
> 
> Keyint has nothing to do with fps. It's the interval between
> successive I (intra) frames. In all modern video codecs, most frames
> are encoded as a difference from a past (or sometimes future) frame.
> Only a few frames are encoded as stand-alone images that can be
> decoded on their own. These are the I frames and they are MUCH larger
> than other frames because they cannot take advantage of similarity to
> adjacent frames.
> 
> However, the vast, vast majority of players can only seek to I frames.
> (Seeking to a non-I frame is basically just seeking to an I frame
> followed by decoding a large number of subsequent frames.) Lowering
> the keyint therefore improves efficient fine-grained seeking, but at
> the expense of compression efficiency. If keyint is 120, that means 1
> I-frame every 120 frames. So if your video is 30 fps, that would be
> one I frame (point you can seek to) every 4 seconds.
> 
> Rich
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Thanks for the very concise answer on that. So I frames are key frames and the keyint is like (forgive the example) the frames used for tweening in flash.

What are the B frames if I can press you further? Are they the interval frames?

How much effect on quality does changing this variable make? Is the quality of the video improved or only the seeking?

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