thumbnailing I frames

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thumbnailing I frames

emanuele fumagalli
Hi all,

Is there a way to get a thumbnail for every Intra frame?

Ususally I use:

ffmpeg -y -i c:\red_bull.mp4 -f image2 -ss 12 -vframes 1 -an pic.png

 

to get a specific second image.

 

Thanks for any help

 

bye

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Re: thumbnailing I frames

Michel Bardiaux-2
emanuele fumagalli a écrit :
> Hi all,
>
> Is there a way to get a thumbnail for every Intra frame?

No, because I-frames are not completely predictable, unless special care
has been taken during encoding.

You will have to modify the source code of ffmpeg.c

>
> Ususally I use:
>
> ffmpeg -y -i c:\red_bull.mp4 -f image2 -ss 12 -vframes 1 -an pic.png
>
>  
>
> to get a specific second image.


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Re: thumbnailing I frames

Adrian Boeing
Hi,

I am also interested in this problem,

>> Hi all,
>>
>> Is there a way to get a thumbnail for every Intra frame?
>>    
>
> No, because I-frames are not completely predictable, unless special care
> has been taken during encoding.
>
> You will have to modify the source code of ffmpeg.c
>  

Would you be able to provide more information as to what needs to be done?

(Virtualdub, for example, lets you very quickly skip between keyframes
for previewing by holding the shift key, and I would like to do the
same...)
(see: http://www.virtualdub.org/docs_processing.html)

Thanks,
-Adrian

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Re: thumbnailing I frames

Michel Bardiaux-2
Adrian Boeing a écrit :

> Hi,
>
> I am also interested in this problem,
>>> Hi all,
>>>
>>> Is there a way to get a thumbnail for every Intra frame?
>>>    
>> No, because I-frames are not completely predictable, unless special care
>> has been taken during encoding.
>>
>> You will have to modify the source code of ffmpeg.c
>>  
>
> Would you be able to provide more information as to what needs to be done?

When av_read_packet returns there is a flag in the packet telling you
whether it's a key frame. A quick-and-dirty way is to use the image2
output container (auto-numbered 1-image files) and automatically delete
the images that do not come from key frames.

>
> (Virtualdub, for example, lets you very quickly skip between keyframes
> for previewing by holding the shift key, and I would like to do the
> same...)

That's a different requirement. av_seek_frame *will* always position you
on a key frame.

Greetings,
--
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Re: thumbnailing I frames

Robert Ramiega
In reply to this post by emanuele fumagalli
  Hi!

On Fri, Dec 14, 2007 at 10:31:45PM +0900, Adrian Boeing wrote:
> Hi,
>
> (Virtualdub, for example, lets you very quickly skip between keyframes
> for previewing by holding the shift key, and I would like to do the
> same...)

 Correct me if I'm wrong but isn't VD scanning file while opening? While
scanning, I guess, it can easily detect which frames are key ones.

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