[Libav-user] Framerate of video is not exact

Wed Apr 28 19:21:49 EEST 2021

Hello,

This seems like an issue I faced with my own attempt at transcoding video
and a fix was suggested by a member of this mailing list (thanks James).
I am not sure that this will resolve your issue but it may, so here goes:

You need to set the AVPacket duration field. This would mean adding
something in the lines of the following line of code before your
av_interleaved_write_frame is called:

// for example, if 25 FPS, and time_base is 12800, then packet.duration =
12800 / 25 = 512
output_packet.duration =
format_context->streams[stream_index]->time_base.den /
format_context->streams[stream_index]->time_base.num /
format_context->streams[stream_index]->avg_frame_rate.num *
format_context->streams[stream_index]->avg_frame_rate.den;

 /* mux encoded frame */
    ret = av_interleaved_write_frame(format_context, output_packet);

Hope this helps!
Vas

On Wed, Apr 28, 2021 at 7:09 PM Exclusive Goods Warehouse <
testchannel256 at gmail.com> wrote:

> Hello,
>
> I'm trying to use "muxing.c" file from the examples. I need to export
> videos in multiple formats with exact fps, let's say 25. I'm using VLC
> player to check the real fps. When i pick .avi format as output, it is
> exactly 25. Hovewer, when i pick .mp4 file, the output video has always
> slightly different framerate, for example 25.166666. This somehow depends
> on duration of the video. Short videos can have even more than 26 fps. This
> does not happen in console tool ffmpeg, just in the file muxing.c. I don't
> want to use the console version though.
> I have no idea how to fix this. Would somebody be so kind and help me?
>
> Here is the output:
>
> [libx264 @ 0x56419e134b00]
> using cpu capabilities: MMX2 SSE2Fast LZCNT SSSE3 SSE4.2 AVX
> [libx264 @ 0x56419e134b00]
> profile High, level 1.3
> [libx264 @ 0x56419e134b00] 264 - core 152 r2854 e9a5903 - H.264/MPEG-4 AVC
> codec - Copyleft 2003-2017 - http://www.videolan.org/x264.html - options:
> cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1
> psy_rd=1,00:0,00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1
> cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=1
> lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0
> bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1
> b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=12 keyint_min=1
> scenecut=40 intra_refresh=0 rc_lookahead=12 rc=abr mbtree=1 bitrate=400
> ratetol=1,0 qcomp=0,60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1,40 aq=1:1,00
> Output #0, mp4, to '/home/****/Videos/test.mp4':
>     Stream #0:0: Video: h264, yuv420p, 352x288, q=2-31, 400 kb/s, 25 tbn
>     Stream #0:1: Audio: aac (LC), 44100 Hz, stereo, fltp, 64 kb/s
> [libx264 @ 0x56419e134b00]
> frame I:13    Avg QP: 9,53  size:  3837
> [libx264 @ 0x56419e134b00] frame P:38    Avg QP: 9,60  size:   974
> [libx264 @ 0x56419e134b00] frame B:100   Avg QP:13,21  size:   970
> [libx264 @ 0x56419e134b00] consecutive B-frames:  8,6%  1,3% 23,8% 66,2%
> [libx264 @ 0x56419e134b00] mb I  I16..4: 77,9% 12,5%  9,7%
> [libx264 @ 0x56419e134b00] mb P  I16..4: 76,4%  4,9%  0,2%  P16..4: 18,1%
>  0,2%  0,3%  0,0%  0,0%    skip: 0,0%
> [libx264 @ 0x56419e134b00] mb B  I16..4:  0,0%  0,0%  0,0%  B16..8: 11,9%
>  0,5%  0,0%  direct:60,1%  skip:27,5%  L0:39,3% L1:56,6% BI: 4,1%
> [libx264 @ 0x56419e134b00] final ratefactor: 6,01
> [libx264 @ 0x56419e134b00] 8x8 transform intra:7,9% inter:39,2%
> [libx264 @ 0x56419e134b00] coded y,uvDC,uvAC intra: 7,0% 15,9% 10,0%
> inter: 0,2% 74,0% 7,7%
> [libx264 @ 0x56419e134b00] i16 v,h,dc,p:  0%  0%  0% 100%
> [libx264 @ 0x56419e134b00] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 19% 17%  6% 57%
>  0%  0%  0%  0%  0%
> [libx264 @ 0x56419e134b00] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 11%  4%  5% 74%
>  4%  0%  0%  2%  1%
> [libx264 @ 0x56419e134b00] i8c dc,h,v,p:  0%  5%  7% 89%
> [libx264 @ 0x56419e134b00] Weighted P-Frames: Y:0,0% UV:0,0%
> [libx264 @ 0x56419e134b00] ref P L0: 98,4%  0,2%  0,6%  0,8%
> [libx264 @ 0x56419e134b00] ref B L0: 90,0%  8,9%  1,1%
> [libx264 @ 0x56419e134b00] ref B L1: 95,9%  4,1%
> [libx264 @ 0x56419e134b00] kb/s:243,60
> [aac @ 0x56419e11d6a0] Qavg: 321,284
>
>
>
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