Re: [Mjpeg-developer] mpeg2enc with MJPEG Tools 1.9.0rc2 buggy !

[stefan <st...@sf...>]

stefan schrieb:
>> First, if you are encoding for DVD do *NOT* use '-q 1 -b 9000'!
>>     
>
> Which is very mpeg2enc related. I now know several encoders (ffmpeg 
> included), which produce a *lot* less bitrate-spikes and seem to avoid 
> them completely in 2-pass-mode ... I have even seen some files where 
> there have not been any spikes...
>
>   
>> If you use "-q 3" or "-q 4" the problem appears to go away.
>>     
> Sorry,... not here... :-(
>   
>> Ideally and eventually '-q' should go away completely.  ALl that should
>> be specified is a desired average bitrate and a tolerance (how much
>> above/below the average is acceptable).
>>   
>>     
> Huh? I don't regard this to be a good idea. There is no harm, if an 
> encoder uses less bits than specified by the bitrate. Imagine a 
> completly black frame: P+B frames could be close to zero-size (just the 
> overhead to say the decoder "same than before"...).
>
> I think, mpeg2enc needs two bitrate-modes:
>
> 1) variable bitrate-mode: A local and short second pass is just used to 
> chop off bitrate-spikes. That is, whenever the encoder realizes that 
> there was a spike, it goes back some frames (a GOP?) and reencodes them 
> with a lower q-scale again. But only for that spike...
>
> 2) average-bitrate-mode or "filesize-mode": Here it makes some sense to 
> specify an upper-bound-tolerance, only.

and in case someone asks... an average-bitrate, of course...

>  The encoder must not go beyond 
> this. If not possible otherwise, then use 2 passes... This mode should 
> fit a file as close as possible to a given file-size/average-bitrate...
>
> hmm,... seems like I must use ffmpeg, currently...
>
> cu
> Stefan
>
>
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