[MEncoder-users] Wrongly guessed bitrates for 2x700 MB CDs

[Loren Merritt]

On Thu, 21 Sep 2006, Dominik 'Rathann' Mierzejewski wrote:
> On Thursday, 21 September 2006 at 12:34, Trent Piepho wrote:
>> On Thu, 21 Sep 2006, Dominik 'Rathann' Mierzejewski wrote:
>>>
>>> Delete the files you got in the -ovc frameno pass and don't use -oac copy
>>> when encoding video. Instead, encode the audio in every video pass.
>>
>> Why does using -oac copy matter in the non-final passes?  It seems like you
>> could use -oac copy for the first pass, and then use -oac mp3lame in the
>> final pass.
>>
>> What would be faster, is if there was a -oac null option, sort of like -ovc
>> frameno.  It wouldn't actually encode any audio, just be a filler for things
>> like bitrate estimating and mutlti-pass encoding.
>
> Doesn't it mess up A-V sync if you use a different audio stream in each pass?
> I thought frameno was deprecated for this reason.

In order to maintain sync, mencoder sometimes has to srop or duplicate 
frames. If you encode with a different audio stream (or no audio), then it 
drops different (or no) frames, which messes up the mapping of 
frame <-> frame number. The video codec depends on that mapping, otherwise 
the 2pass algorithm doesn't work.

--Loren Merritt