[FFmpeg-user] Framerate Question

Jared McIntyre jmcintyre at dfsoftware.com
Mon Mar 5 04:02:22 CET 2012

I'm re-encodeing broadcast video. The source was apparently 720 30fps, but is being broadcast 60fps where every frame appears twice. I thought I'd try to save some space by re-encoding and using 30fps to cut out every other frame. I used the following command:

ffmpeg -i in.mpg -acodec libfaac -ab 160k -crf 23.1 -vcodec libx264 -tune animation -preset faster -profile baseline -f mp4 -r 29.97 out.mp4

I was a bit surprised to find out that if I used -r 29.97 I would get a file with half the frames, but a larger size than if I hadn't done so. I'm sure I'm misunderstanding something, but is this the expected behavior? Here is the log data in case about the encodeing:

Seems stream 0 codec frame rate differs from container frame rate: 119.88 (120000/1001) -> 59.96 (90000/1501)
Input #0, mpeg, from 'in.mpg':
  Duration: 00:02:30.91, start: 0.328367, bitrate: 11748 kb/s
    Stream #0.0[0x1e0]: Video: mpeg2video (Main), yuv420p, 1280x720 [PAR 1:1 DAR 16:9], 38810 kb/s, 59.96 fps, 59.96 tbr, 90k tbn, 119.88 tbc
    Stream #0.1[0x80]: Audio: ac3, 48000 Hz, 5.1, s16, 384 kb/s
[buffer @ 0x101a33900] w:1280 h:720 pixfmt:yuv420p tb:1/1000000 sar:1/1 sws_param:
[libx264 @ 0x10204a000] using SAR=1/1
[libx264 @ 0x10204a000] using cpu capabilities: MMX2 SSE2Fast SSSE3 FastShuffle SSE4.1 Cache64
[libx264 @ 0x10204a000] profile Constrained Baseline, level 3.1
[libx264 @ 0x10204a000] 264 - core 115 - H.264/MPEG-4 AVC codec - Copyleft 2003-2011 - http://www.videolan.org/x264.html - options: cabac=0 ref=4 deblock=1:1:1 analyse=0x1:0x111 me=hex subme=4 psy=1 psy_rd=0.40:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=1 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=0 threads=3 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=0 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=20 rc=crf mbtree=1 crf=23.1 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:0.60
Output #0, mp4, to 'out.mp4':
    encoder         : Lavf52.110.0
    Stream #0.0: Video: libx264, yuv420p, 1280x720 [PAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 2997 tbn, 29.97 tbc
    Stream #0.1: Audio: libfaac, 48000 Hz, 5.1, s16, 160 kb/s
Stream mapping:
  Stream #0.0 -> #0.0
  Stream #0.1 -> #0.1

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