Re: [Mlt-devel] [filter avfilter.crop] Unexpected return format

[Dan D. <da...@de...>]

Multiple instances of crop is simply not supported/possible.

On Tue, Oct 11, 2016, 2:20 PM Geoffroy Montel <geo...@gm...>
wrote:

Dear Dan

Many thanks for your quick answer. It makes perfectly sense !

I've always used melt native crop, and it's great, but I'm facing a slight
issue right now when chaining two native crops. That's why I was starting
to test avfilter crop.

Anyway, let's share my experiment with chaining two native crops :

Let's say I have this picture :
http://thepopmanifesto.com/issue09/images/content/kindness-2.jpg
Image size is 642px x 800px

1. If I want to crop center this picture, the picture aspect ratio is
preserved

melt kindness-2.jpg in=0 out=100 -attach-track crop center=1 -profile
hdv_720_25p -consumer avformat:kindness.mp4

Good !

2. If I want to crop the source image from (0,0) to (300,300), the picture
aspect ratio is preserved and I only get the top left section of the image,
centered in the screen

melt kindness-2.jpg in=0 out=100 -attach-clip crop left=0 top=0 right=342
bottom=500 -profile hdv_720_25p -consumer avformat:kindness.mp4

Good !

3. If I want to chain the two crops, which means I want to take the top
left section of the image, then center crop it to remove black borders, it
does not work

melt kindness-2.jpg in=0 out=100 -attach-clip crop left=0 top=0 right=342
bottom=500 -attach-track crop center=1 -profile hdv_720_25p -consumer
avformat:kindness.mp4

First, I don't see a portion of the top left corner of the image and
second, the image aspect ratio is not preserved.

Of course this example is oversimplified, I would not have to chain two
crops, but only one crop with the right 16/9 ratio.
It only makes sense when I'm also adding affine transitions between the
left/top/right/bottom crop and the center crop.

Let me know if I'm not taking the right approach !

Thanks again for your time and patience, all the best

Geoffroy




2016-10-11 8:21 GMT+02:00 Dan Dennedy <da...@de...>:

Well, basically, many avfilters are simply incompatible, and we blacklist
some, but we have not taken the time to audit all of them, and they are
adding many all the time. In this case, the error occurs because the output
width and height do not match the width and height that MLT needs - as
expected for a crop. In MLT, at some point, all video frames need to
conform in order to allow mixing or to give the output consumer what it
requested in a consistent manner. For that MLT automatically adds
normalization filters to deinterlace, change field order, scale, pad,
resample audio, correct # audio channels, etc. MLT's native crop filter is
special because it has two pars: one that is first in normalization and one
the user adds that directs the first one. This allows the scaling and
padding filters to apply to the output of the first part. In short,
avfilter.crop cannot work in MLT, and you should use the MLT crop filter.
In the context of all of this, crop has an interesting behavior that you
can observe in shotcut or similar. You first need to figure out what
resolution and aspect ratio you want as a result, use that as a MLT
profile, and then crop. You cannot simply say take this input crop X from
top and bottom, compute the result for me, and give it to me.

On Mon, Oct 10, 2016 at 11:09 PM Geoffroy Montel <
geo...@gm...> wrote:

Dear list,

I've been trying to use avfilter crop filter, but I'm getting some errors.

melt crop.jpg in=0 out=100 -attach avfilter.crop av.x=0 av.y=0 av.out_w=300
av.out_h=300 -progress -consumer avformat:crop.mp4

returns

[filter avfilter.crop] Unexpected return format

and the image is not cropped.

Am I doing something wrong ?

Thanks in advance for your help, all the best

geoffroy

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