[FFmpeg-user] problem with limitng output bitrate and VBV underflow warning

negin tebyani negin.tebyani at gmail.com
Sun Apr 9 11:27:17 EEST 2017


forgot to show mediainfo output:

General
Complete name                            : 300from12000.mp4
Format                                   : MPEG-4
Format profile                           : Base Media
Codec ID                                 : isom
File size                                : 18.2 MiB
Duration                                 : 1mn 0s
Overall bit rate                         : 2 547 Kbps
Writing application                      : Lavf56.25.101

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High at L5.0
Format settings, CABAC                   : Yes
Format settings, ReFrames                : 16 frames
Codec ID                                 : avc1
Codec ID/Info                            : Advanced Video Coding
Duration                                 : 1mn 0s
Bit rate                                 : 2 219 Kbps
Nominal bit rate                         : 300 Kbps
Width                                    : 1 280 pixels
Height                                   : 720 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 50.000 fps
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.048
Stream size                              : 15.9 MiB (87%)
Writing library                          : x264 core 142 r2495 6a301b6
Encoding settings                        : cabac=1 / ref=16 / deblock=1:1:1
/ analyse=0x3:0x133 / me=umh / subme=10 / psy=0 / mixed_ref=1 / me_range=16
/ chroma_me=1 / trellis=2 / 8x8dct=1 / cqm=0 / deadzone=21,11 /
fast_pskip=1 / chroma_qp_offset=0 / threads=4 / lookahead_threads=1 /
sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 /
constrained_intra=0 / bframes=10 / b_pyramid=2 / b_adapt=2 / b_bias=0 /
direct=3 / weightb=1 / open_gop=0 / weightp=2 / keyint=288 / keyint_min=24
/ scenecut=42 / intra_refresh=0 / rc_lookahead=60 / rc=cbr / mbtree=1 /
bitrate=300 / ratetol=1.0 / qcomp=0.60 / qpmin=0 / qpmax=35 / qpstep=4 /
vbv_maxrate=300 / vbv_bufsize=1000 / nal_hrd=none / filler=0 /
ip_ratio=1.40 / aq=1:0.00
Language                                 : English

Audio
ID                                       : 2
Format                                   : AAC
Format/Info                              : Advanced Audio Codec
Format profile                           : LC
Codec ID                                 : 40
Duration                                 : 1mn 0s
Duration_LastFrame                       : -11ms
Bit rate mode                            : Constant
Bit rate                                 : 320 Kbps
Channel count                            : 2 channels
Channel positions                        : Front: L R
Sampling rate                            : 48.0 KHz
Compression mode                         : Lossy
Delay relative to video                  : 40ms
Stream size                              : 2.29 MiB (13%)
Language                                 : English


On Sun, Apr 9, 2017 at 12:56 PM, negin tebyani <negin.tebyani at gmail.com>
wrote:

> I am using this commad to transcode a video with 12000k bitrate to a lower
> bitrate like 300k.
>
> here is my command:
>
> ffmpeg -i 12000.mp4 -movflags faststart -c:v libx264 -x264opts
> 'keyint=288:min-keyint=24:8x8dct:sliced-threads=0' -deblock 1:1 -flags
> +loop -b:v 300k -maxrate 300k -bufsize 1000k -tune psnr  -vf
> "scale=-1280:720:flags=spline+full_chroma_inp+full_chroma_int+accurate_rnd+bitexact"
> -acodec libfdk_aac -b:a 320k -coder 1 -me_range 16 -sc_threshold 42 -bf 10
> -q:v 1 -qmin 0 -qmax 35 -trellis 2 -mbtree 1 -mixed-refs 1 -preset veryslow
> video.mp4
>
> I need the bitrate to be 2000, but after using this command and using
> media info, I see that bitrate is different from what I specified (2000 for
> ecample) and there is a nominal bitrate which is what I specified in my
> command.
>
> and during the convert process i get the VBV underflow warning after a
> short time passes. until that warning hasn't showed up, the bitrate seems
> to be fine. but after that the bitrate starts to get higher.
>
> here is my console output:
>
> [libx264 @ 0x20bb0c0] VBV underflow (frame 2992, -20064 bits)
> [libx264 @ 0x20bb0c0] VBV underflow (frame 2993, -13888 bits)
> [libx264 @ 0x20bb0c0] VBV underflow (frame 2995, -520 bits)
> [libx264 @ 0x20bb0c0] VBV underflow (frame 2996, -992 bits)
> [libx264 @ 0x20bb0c0] VBV underflow (frame 2997, -1320 bits)
> [libx264 @ 0x20bb0c0] VBV underflow (frame 2998, -9528 bits)
> [libx264 @ 0x20bb0c0] VBV underflow (frame 2999, -744 bits)
> [mp4 @ 0x20ba1e0] Starting second pass: moving the moov atom to the
> beginning of the file
> frame= 3000 fps= 13 q=-1.0 Lsize=   18665kB time=00:01:00.01
> bitrate=2547.9kbits/s
> video:16252kB audio:2346kB subtitle:0kB other streams:0kB global
> headers:0kB muxing overhead: 0.363480%
> [libx264 @ 0x20bb0c0] frame I:15    Avg QP:30.80  size: 46683
> [libx264 @ 0x20bb0c0] frame P:592   Avg QP:31.14  size: 16537
> [libx264 @ 0x20bb0c0] frame B:2393  Avg QP:34.69  size:  2570
> [libx264 @ 0x20bb0c0] consecutive B-frames:  0.8%  3.3%  5.4%  9.6%  3.3%
> 76.2%  0.7%  0.0%  0.6%  0.0%  0.0%
> [libx264 @ 0x20bb0c0] mb I  I16..4: 37.0% 48.8% 14.2%
> [libx264 @ 0x20bb0c0] mb P  I16..4:  9.1%  9.4%  1.0%  P16..4: 24.2%  7.5%
>  5.7%  0.8%  0.1%    skip:42.2%
> [libx264 @ 0x20bb0c0] mb B  I16..4:  0.4%  0.2%  0.0%  B16..8: 17.9%  4.2%
>  0.7%  direct: 0.9%  skip:75.6%  L0:37.7% L1:49.0% BI:13.3%
> [libx264 @ 0x20bb0c0] 8x8 transform intra:46.4% inter:49.8%
> [libx264 @ 0x20bb0c0] direct mvs  spatial:99.9% temporal:0.1%
> [libx264 @ 0x20bb0c0] coded y,uvDC,uvAC intra: 18.8% 27.9% 7.3% inter:
> 5.6% 3.5% 0.3%
> [libx264 @ 0x20bb0c0] i16 v,h,dc,p: 29% 46% 10% 15%
> [libx264 @ 0x20bb0c0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 11% 19% 55%  3%  2%
>  3%  3%  2%  3%
> [libx264 @ 0x20bb0c0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 26% 30% 17%  3%  5%
>  6%  5%  4%  4%
> [libx264 @ 0x20bb0c0] i8c dc,h,v,p: 65% 20%  8%  6%
> [libx264 @ 0x20bb0c0] Weighted P-Frames: Y:5.6% UV:4.6%
> [libx264 @ 0x20bb0c0] ref P L0: 57.1% 15.8% 13.9%  3.3%  2.4%  1.7%  1.3%
>  0.6%  0.6%  0.8%  0.5%  0.4%  0.4%  0.4%  0.4%  0.3%
> [libx264 @ 0x20bb0c0] ref B L0: 84.1%  9.0%  2.3%  1.4%  0.6%  0.6%  0.6%
>  0.2%  0.2%  0.3%  0.2%  0.2%  0.1%  0.1%  0.1%
> [libx264 @ 0x20bb0c0] ref B L1: 96.4%  3.6%
> [libx264 @ 0x20bb0c0] kb/s:2218.78
>
>
> and here is a demo of video:
>
> https://streamable.com/e6dbg
>
>
>
>
>
>
>


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