[MEncoder-users] mkv to hard sub avi to m4v command line options and sync problems

[James Hastings-Trew]

Reimar Döffinger wrote:
> On Sun, Jan 17, 2010 at 07:55:06AM -0600, James Hastings-Trew wrote:
>   
>> Reimar Döffinger wrote:
>>     
>>> On Sun, Jan 17, 2010 at 07:17:06AM -0600, James Hastings-Trew wrote:
>>>       
>>>> v4r4n wrote:
>>>>         
>>>>> $> mencoder -oac copy -ovc raw -sub subtitles.srt -sub-bg-alpha 255 -utf8 -o
>>>>> output.srt.avi input.avi
>>>>>
>>>>> to make a large raw with baked subtitles, then Handbrake to re-encode that
>>>>> into an iPod .m4v file.  This works well enough, but the original visual
>>>>> artifacts that I saw in the raw are still there.
>>>>>           
>>>> I'm not sure how you could expect it to be otherwise. That command
>>>> line leads me to believe the artifacts are part of the original .mkv
>>>> file, since raw would not add any artifacts of it's own.
>>>>         
>>> Wrong, it will introduce decoding errors if you do not use -noskip.
>>>       
>> Are you saying that it will skip decoding frames, not just skip
>> storing them?
>>     
>
> ?? No idea what you mean.
> I mean it will skip storing the encoded data belong to whatever
> frame it decides to drop, and that frame may have been referenced
> by later encoded frames which is does copy - this breaks decoding
> of those frames.
> So with -ovc raw and an encoded format a skipped frame (as can happen
> when you do not use -noskip) can mean there is one frame missing in
> the resulting frame and there are possible another several 100
> that are there bug can not be decoded correctly.
> For those that can not be decoded correctly, FFmpeg uses error-concealment
> and since that is quite good you usually see it only as the output
> looking blocky, blurry or otherwise low quality.
> The error-concealment can be tuned with -lavdopts ec=...  but it seems
> it can't be disabled...
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>   
I thought -ovc raw just stored uncompressed video, not encoded frames.