[FFmpeg-devel] [PATCH] add top video filter

Mark Himsley mark at mdsh.com
Mon Mar 28 21:35:19 CEST 2011

On 28/03/2011 19:39, Michael Niedermayer wrote:
> On Mon, Mar 28, 2011 at 02:47:20PM +0100, Mark Himsley wrote:
>> Dear developers,
>> Converting to and from interlaced PAL DV files, with their  
>> bottom-field-first interlace field order, can be a pain. Converting tff  
>> files to DV results in tff DV files, which are hard to work with in  
>> editing software.
>> The attached filter can:
>> Convert field order by either moving all of the lines in the picture up  
>> by 1 line (bff to tff conversion) or down by 1 line (tff to bff  
>> conversion). The remaining line, the bottom line in bff to tff  
>> transforms or the top line in tff to bff transforms, is filled by  
>> copying the closest line in that field.
>> Previous to this filter I have used a filter chain like this to do bff  
>> to tff conversion.
>> format=yuv422p,crop=720:575:0:1,pad=720:576:0:0:black
>> but that chain does not fill the remaining line.
>> -- 
>> Mark
>>  doc/filters.texi         |   29 +++++++
>>  libavfilter/Makefile     |    1 
>>  libavfilter/allfilters.c |    1 
>>  libavfilter/vf_top.c     |  184 +++++++++++++++++++++++++++++++++++++++++++++++
> i think vshift or vmove or something like that is a better name

I chose the filter name 'top' to match the -top command. I'm not keen on
vshift or vmove because, in my mind, they don't describe the purpose of
the filter - to change between top and bottom field first.

But it's only a name, so it's not something I'm going to stress about :-)

> off topic a bit:
> also theres another way to convert between top & bottom field first
> and that is to combine 2 fields from 2 seperate frames

Yes indeed. Removing the very first field and the very last field from a
clip will also swap the fields of the whole clip. But the down sides are
that you've lost a whole frame off the clip's duration and, more
importantly, video cuts which were on frame boundaries are now in the
middle of frames - making re-editing much more difficult.

Back on topic...

> [...]
>> +static int query_formats(AVFilterContext *ctx)
>> +{
>> +    enum PixelFormat pix_fmts[] = {
>> +        PIX_FMT_YUV444P,  PIX_FMT_YUV422P,
>> +        PIX_FMT_YUVJ444P, PIX_FMT_YUVJ422P,
>> +        PIX_FMT_RGB24,    PIX_FMT_BGR24,
>> +        PIX_FMT_ARGB,     PIX_FMT_ABGR,
>> +        PIX_FMT_RGBA,     PIX_FMT_BGRA,
>> +        PIX_FMT_NONE
>> +    };
> i think the filter could easily be made to support more formats

It won't currently support formats with half-vertical resolution chroma.
I think it's beyond my mathematical capabilities to move that chroma up
of down by half a line.

Or perhaps this filter should leave the half-vertical resolution chroma
where it is... I think some experiments need to be done with chroma-key
recorded on DV and converted to IMX-30, for instance.

But, yes, you're right that this might not be a complete list of formats
that can be supported by this filter.



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