[FFmpeg-devel] [PATCH] Change default behaviour of scale filter from 'progressive' to 'auto'

Tim Nicholson nichot20 at yahoo.com
Wed Apr 4 16:15:08 CEST 2012

----- Original Message -----
> From: Baptiste Coudurier <baptiste.coudurier at gmail.com>
> To: FFmpeg development discussions and patches <ffmpeg-devel at ffmpeg.org>
> Cc: Tim Nicholson <nichot20 at yahoo.com>
> Sent: Wednesday, 4 April 2012, 2:48
> Subject: Re: [FFmpeg-devel] [PATCH] Change default behaviour of scale filter from 'progressive' to 'auto'
> On 04/03/2012 09:07 AM, Tim Nicholson wrote:
>>  diff --git a/tests/ref/vsynth1/dnxhd_1080i b/tests/ref/vsynth1/dnxhd_1080i
>>  index f8f6df0..de4732e 100644
>>  --- a/tests/ref/vsynth1/dnxhd_1080i
>>  +++ b/tests/ref/vsynth1/dnxhd_1080i
>>  @@ -1,4 +1,4 @@
>>   027c985483caab9397592bf27477dce1 *./tests/data/vsynth1/dnxhd-1080i.mov
>>   3031911 ./tests/data/vsynth1/dnxhd-1080i.mov
>>  -0c651e840f860592f0d5b66030d9fa32 *./tests/data/dnxhd_1080i.vsynth1.out.yuv
>>  -stddev:    6.29 PSNR: 32.15 MAXDIFF:   64 bytes:   760320/  7603200
>>  +3c3226518a0f56468bf56a6682e31fae *./tests/data/dnxhd_1080i.vsynth1.out.yuv
>>  +stddev:   14.22 PSNR: 25.07 MAXDIFF:  119 bytes:   760320/  7603200
> A default change that produces a difference like this is unacceptable IMHO.
> This is quite a big difference.

If this was a real world case would agree. However the fate test deliberately puts progressive material in an interlaced stream, and then back again. If you do the same round trip with interlaced material the results are very different. The results are only worse because the stream is being handled in the format it claims to be, rather than blindly handled progressively.

Should we not have a more realistic fate test?

Is it really sensible for the default mode to handle interlaced material as progressive so that every time a scale filter is auto inserted there is a risk of degradation if it is not spotted and replaced with a manually configured instance?

It is surely better to handle material according to the way it is flagged, and then override the flag if it is believed to be wrong.

It will be interesting to see the figures adding in Michaels new interlace detect feature.....

> -- 
> Baptiste COUDURIER



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