________________________________
From: Brian Matherly <pez4br...@yahoo.com>
To: James Board <jpboa...@yahoo.com>; Dan Dennedy <d...@dennedy.org>
Cc: "mlt-devel@lists.sourceforge.net" <mlt-devel@lists.sourceforge.net>
Sent: Tuesday, July 23, 2013 5:41 PM
Subject: Re: [Mlt-devel] Delete segments from input video file, output to
another file
>>> I'm a new melt user. I want to do something simple. I'd like to take
>>> an existing avi file (in a raw format: no inter-frame compression like
>>> mpeg) and delete some segments. I tried a simple command like this
>>>
>>> melt InFile.avi in=80 out=120 -consumer avformat:OutFile.avi
>>>
>>> My intent was that only frames 80 to 120 will be in the output
>>> file OutFile.avi. But when I view OutFile.avi, all frames are the same
>>> as frame 80 in the input file. So this did not
>work.
>>>
>>> How can I correctly use melt to delete segments from an AVI file?
>>
>>That is correct, but probably your AVI is not seekable or readable by
>>libavformat or MLT, or the particular version of libavformat your MLT
>>build is using requires some more avformat encoding parameters to be
>>set. I suggest that you use Shotcut to get acquainted with MLT and try
>>some things out. Look at the XML it generates. See if it can play and
>>seek on the file you are trying to read.
>
>Thanks for your help. The AVI file was generated by mencoder, so if
>melt uses the same libraries that mencoder uses, then it should be
>readable? DOes that make sense? Anyway, what is 'shotcut'?
>Did you mean 'shortcut'? I searched on the MLT documentation
>page http://www.mltframework.org/bin/view/MLT/Documentation
>for either and it didn't find anything.
>Thanks.
Shotcut is essentially a GUI wrapper around the MLT library. I think the reason
that Dan suggested that you look at it is because sometimes it can be easier to
discover things by visual inspection and "clicking around" until you achieve
your desired result.
Another thing you can try is to use melt without specifying the consumer. If
you do that, melt automatically selects the SDL consumer and the result is
displayed on your screen. This way you can immediately see the result without
opening the file in an player each time.
mencoder and mlt both use libavcodec under the hood to provide codec support.
Just because libavcodec can encode a particular codec does not necessarily mean
it can decode it. You would have to check the codec support for the particular
codec you are using. As an experiment, it would be interesting to use a more
common codec to see if you can achieve the desired result. For example, use
mencoder to encode the video as mpeg2 and see if it works with melt the way you
want.
~BM
I tried about 10 different video formats and could not get melt to
work correctly with any of them. When I try to extract my video segment
melt doesn't print any errors, and when I try to play the extracted
segment, it shows the first image in the segment, which is the
proper image. So, I think melt must understand that format. But
the problem is that all of the extracted frames are the same as that
first frame.
Many of the input formats I tried were raw formats were each frame was
stored whole and the pixels were in a YUV or RGB format. I was
thinking that would be the lowest common denominator and should
work with anything. I also tried mpeg2 formats as well.
If I try to play the file to the screen without specifying a consumer,
melt usually displays a single image, then no other. However, in the
xterm where I ran melt, it displays successive frame numbers as if
everything is playing normally.
If you can provide a simple ffmpeg command to convert my video
to a format that melt supports, please send it to me. Or, if you can
let me know which format melt supports, that would be good.
I'd rather not spend however much time building a complex
GUI based on MLT if MLT doesn't support any of the formats
that my video is in.
Thanks.
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