[FFmpeg-user] Confusion about fieldmatch, decimate and framerate (now with yadif)

Nicholas Robbins nickrobbins at yahoo.com
Thu Dec 12 19:02:06 CET 2013

> On Thursday, December 12, 2013 11:25 AM, L. Lee <llee040 at sbcglobal.net> wrote:

> > On 12/9/13, 8:44 PM, "Nicholas Robbins" <nickrobbins at yahoo.com> 
> wrote:
>> The 'decimate' filter after fieldmatch would take care of the frame 
> rate
>> coversion, but it just throws out the extra frame, so it wouldn't change
>> the fact that fieldmatch was labeling frames as interlaced, but yadif
>> wasn't deinterlacing them.
> That hasn¹t been my experience at all. The frame rate of the output may be
> the same, but unless the filter chain and all other options are the same,
> the encoding results might be entirely different.
> Laine Lee

I'm not sugesting that it would be identical, but it seems that the problem is between fieldmatch and yadif so tacking ,decimate onto the end would not change if yadif caught the frames. I tested and the I get the "still interlaced" frames at the same places.

Frame #8158 at 272.205 is still interlaced time=00:04:31.96 bitrate=2607.8kbits/s    
[Parsed_fieldmatch_1 @ 0x306d9d4f20] Frame #8159 at 272.239 is still interlaced
[Parsed_fieldmatch_1 @ 0x306d9d4f20] Frame #8160 at 272.272 is still interlaced

Furthermore, if decimate does its job right the frame rate is already 24000/1001 since it was 30000/1001 and decimate drops every fifth frame. I checked and the decimated version has a frame rate of 23.97. So I don't thinking adding the fps filter at the end should change things. Also, I just checked, and it doesn't. Same output and error.


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