Why does avconv change the fps when deinterlacing?

I have a .MTS 1080i of 25fps (mediainfo) that I deinterlaced with avconv -i input.MTS -vf yadif -c:a copy output.mp4. As the wiki says, the default value for yadif is 0 which "outputs one frame for each frame".

My question is, why does output.mp4 have 50fps? Also, is it normal that it is much smaller than the input?

As requested:

wantoast@crunchbang:~/videos/video/videocamera$ avconv -i 00000.MTS
avconv version 0.8.16-6:0.8.16-1, Copyright (c) 2000-2014 the Libav developers
  built on Sep 16 2014 23:10:48 with gcc 4.7.2
Input #0, mpegts, from '00000.MTS':
  Duration: 00:00:37.44, start: 1.000033, bitrate: 16506 kb/s
  Program 1 
    Stream #0.0[0x1011]: Video: h264 (High), yuv420p, 1920x1080 [PAR 1:1 DAR 16:9], 50 fps, 50 tbr, 90k tbn, 50 tbc
    Stream #0.1[0x1100]: Audio: ac3, 48000 Hz, stereo, s16, 256 kb/s
    Stream #0.2[0x1200]: Subtitle: pgssub
At least one output file must be specified

wantoast@crunchbang:~/videos/video/videocamera$ avconv -i 00000.MTS -vf yadif -c:a copy output.mp4
avconv version 0.8.16-6:0.8.16-1, Copyright (c) 2000-2014 the Libav developers
  built on Sep 16 2014 23:10:48 with gcc 4.7.2
Input #0, mpegts, from '00000.MTS':
  Duration: 00:00:37.44, start: 1.000033, bitrate: 16506 kb/s
  Program 1 
    Stream #0.0[0x1011]: Video: h264 (High), yuv420p, 1920x1080 [PAR 1:1 DAR 16:9], 50 fps, 50 tbr, 90k tbn, 50 tbc
    Stream #0.1[0x1100]: Audio: ac3, 48000 Hz, stereo, s16, 256 kb/s
    Stream #0.2[0x1200]: Subtitle: pgssub
[buffer @ 0xa5eb40] w:1920 h:1080 pixfmt:yuv420p
[yadif @ 0xa5cba0] mode:0 parity:-1 auto_enable:0
[libx264 @ 0xa59b00] using SAR=1/1
[libx264 @ 0xa59b00] using cpu capabilities: MMX2 SSE2Fast SSSE3 FastShuffle SSE4.2 AVX
[libx264 @ 0xa59b00] profile Main, level 4.2
[libx264 @ 0xa59b00] 264 - core 123 r2189 35cf912 - H.264/MPEG-4 AVC codec - Copyleft 2003-2012 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x1:0x111 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=1 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=6 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=0 b_adapt=1 b_bias=0 direct=1 weightb=0 open_gop=1 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.25 aq=1:1.00
Output #0, mp4, to 'output.mp4':
  Metadata:
    encoder         : Lavf53.21.1
    Stream #0.0: Video: libx264, yuv420p, 1920x1080 [PAR 1:1 DAR 16:9], q=-1--1, 50 tbn, 50 tbc
    Stream #0.1: Audio: ac3, 48000 Hz, stereo, 256 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (h264 -> libx264)
  Stream #0:1 -> #0:1 (copy)
Press ctrl-c to stop encoding
frame= 1870 fps= 16 q=-1.0 Lsize=   29093kB time=37.38 bitrate=6375.8kbits/s dup=935 drop=0    
video:27902kB audio:1170kB global headers:0kB muxing overhead 0.070776%
[libx264 @ 0xa59b00] frame I:122   Avg QP:22.47  size: 49023
[libx264 @ 0xa59b00] frame P:1748  Avg QP:25.43  size: 12923
[libx264 @ 0xa59b00] mb I  I16..4: 61.9%  0.0% 38.1%
[libx264 @ 0xa59b00] mb P  I16..4:  2.8%  0.0%  0.5%  P16..4: 36.5%  2.8%  1.7%  0.0%  0.0%    skip:55.7%
[libx264 @ 0xa59b00] coded y,uvDC,uvAC intra: 38.5% 80.0% 19.8% inter: 7.1% 27.2% 0.2%
[libx264 @ 0xa59b00] i16 v,h,dc,p: 35% 18% 15% 31%
[libx264 @ 0xa59b00] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 28% 18% 35%  4%  3%  3%  4%  3%  2%
[libx264 @ 0xa59b00] i8c dc,h,v,p: 50% 18% 26%  6%
[libx264 @ 0xa59b00] Weighted P-Frames: Y:1.1% UV:0.7%
[libx264 @ 0xa59b00] ref P L0: 63.3%  9.7% 13.0% 13.9%  0.1%
[libx264 @ 0xa59b00] kb/s:6111.45

wantoast@crunchbang:~/videos/video/videocamera$ avconv -i output.mp4 
avconv version 0.8.16-6:0.8.16-1, Copyright (c) 2000-2014 the Libav developers
  built on Sep 16 2014 23:10:48 with gcc 4.7.2
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x216e460] multiple edit list entries, a/v desync might occur, patch welcome
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf53.21.1
  Duration: 00:00:37.47, start: 0.000000, bitrate: 6358 kb/s
    Stream #0.0(und): Video: h264 (Main), yuv420p, 1920x1080 [PAR 1:1 DAR 16:9], 6111 kb/s, 50 fps, 50 tbr, 50 tbn, 100 tbc
    Stream #0.1(und): Audio: ac3, 48000 Hz, stereo, s16, 256 kb/s
At least one output file must be specified

Wantoast

Posted 2014-10-19T16:02:13.373

Reputation: 31

Please include the full command-line output of your conversion command as well as avconv -i output.mp4. – slhck – 2014-10-19T16:26:01.497

1As for your second question: Yes, because it uses the default options to re-encode the video bitstream, which is likely to result in a low bitrate and consequently in low quality output. – slhck – 2014-10-19T16:30:01.750

Added. And how can I know what these defaults are exactly? – Wantoast – 2014-10-19T17:00:42.217

Hm, I don't know why it doesn't show 25. The original should be 50 fields per second, yielding 25 frames. The output should just show 25 fps. The default encoder for your build is x264, which uses a Constant Rate Factor of 23 to encode. This is a sensible default, so it's not a big issue in your case. You can use -crf 18 to force better quality, for example.

– slhck – 2014-10-19T17:42:41.313

The default x264 options for some reason aren't using 8x8dct. Does avconv target the h.264 main profile (instead of the normal high profile) for .mp4 output? Use -preset slower -crf 18 (or whatever, but 18 is usually transparent). Use -profile high if it's still not using 8x8dct=1, unless you're targeting obsolete devices which don't support it. Use a lossless codec instead (huffyuv maybe?) if you're going to edit after deinterlacing, before encoding to a final file. – Peter Cordes – 2014-12-26T19:52:55.753

Why does avconv change the fps when deinterlacing?

No answers