[FFmpeg-user] set image width only?

[Tim Nicholson]

On 09/09/11 07:20, Tim Nicholson wrote:
> On 09/09/11 03:35, lovelove wrote:
>>
>> lovelove wrote:
>>>
>>> I don't really understand the difference between
>>> *-s 400x300*
>>> and
>>> *-vf "scale=400:300"*
>>>
>>
>> Aside from the difference from the -s parameter being unclear,
>> the -vf scale parameter you suggested to me somehow interferes with key
>> frame detection.
>>
>> This extracts all key frames of a video as single images:
>> *ffmpeg.exe -i inputfile.avi -vf select="eq(pict_type\,PICT_TYPE_I)"
>> -vsync
>> 0 -f image2 outputfile.AVI-%03d.tif**
>>
>> But when adding -vf scale, *ALL* images are extracted, not just
>> keyframes:
>> *ffmpeg.exe -i inputfile.avi -vf select="eq(pict_type\,PICT_TYPE_I)"
>> -vsync
>> 0 -vf "scale=400:-1" -f image2 outputfile.AVI-%03d.tif**
>>
>> What's going wrong? thank you.
>>
>
> At a guess, because you haven't ordered the filters the resize is
> happening first and therefore all frames become keyframes...
>
> You need to take the ouptut of the select and feed it into the scale...
>
> Try:-
>
> ffmpeg.exe -i inputfile.avi -vsync 0 -vf
> "select=eq(pict_type\,PICT_TYPE_I) [select]; [select] scale=400:-1
> [out]" -f image2 outputfile.AVI-%03d.tif
>
>

And before someone else points it out, this can be simplified to:-

ffmpeg.exe -i inputfile.avi -vsync 0 -vf 
"select=eq(pict_type\,PICT_TYPE_I), scale=400:-1" -f image2 
outputfile.AVI-%03d.tif

Read up on http://ffmpeg.org/ffmpeg.html#SEC113 about the filtergraph 
syntax.

-- 
Tim

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