[FFmpeg-user] Question about CBR bit rate settings

Wed Apr 19 18:42:04 EEST 2017

I think you're right, the tutorial is probably outdated.

On 4/15/17, Gil Yoder <gil.yoder at oabs.org> wrote:
> According to Korbel in *FFmpeg Basics*, "To set the constant bit rate for
> the output, three parameters must have the same value: bitrate (-b option),
> minimal rate (-minrate) and maximal rate (-maxrate)" (p. 62). That makes
> sense as far as it goes, but it is a bit unclear in my mind. It appears to
> me that -minrate and -maxrate effect only the video output. Is that right?
>
>
>
> If so, -b:v should be used instead of -b, along with -maxrate and -minrate
> to set the CBR of the video stream if the output has both audio and video.
> Is that correct?
>
>
>
> In such, the total bit rate will be the sum of the -b:v and -b:a options
> plus the demuxing overhead. Please, correct me if that's not right.
>
>
>
> I ask because I'm trying to construct an argument to produce a low bitrate
> live stream. So far I've come up with the following argument:
>
>
>
> ffmpeg -hide_banner -f dshow -sample_rate 11025 -video_size qvga -i
> video="HP Deluxe Webcam KQ246AA":audio="Microphone (Logitech USB Headset)"
> -f flv -r 15 -c:v libx264 -crf 30 -preset veryfast -maxrate 96k -minrate 96k
> -b:v 96k -bufsize 198k -pix_fmt yuv420p -g 30 -c:a aac -b:a 24k -metadata
> copyright="Copyright 2017 OABS" -metadata artist="Gil Yoder"
> "rtmp://***.****.***/live3/yoder?u=gil&e=1492253342&h=32628F7B51A3943A9D57FE
> 1B9D389328"
>
>
>
> This is the output for a short session:
>
>
>
> Guessed Channel Layout for Input Stream #0.1 : stereo
>
> Input #0, dshow, from 'video=HP Deluxe Webcam KQ246AA:audio=Microphone
> (Logitech USB Headset)':
>
>   Duration: N/A, start: 342651.162000, bitrate: N/A
>
>     Stream #0:0: Video: rawvideo (YUY2 / 0x32595559), yuyv422, 320x240, 30
> fps, 30 tbr, 10000k tbn, 10000k tbc
>
>     Stream #0:1: Audio: pcm_s16le, 11025 Hz, stereo, s16, 352 kb/s
>
> Stream mapping:
>
>   Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
>
>   Stream #0:1 -> #0:1 (pcm_s16le (native) -> aac (native))
>
> Press [q] to stop, [?] for help
>
> [libx264 @ 00000000025760a0] using cpu capabilities: MMX2 SSE2Fast SSSE3
> SSE4.2 AVX
>
> [libx264 @ 00000000025760a0] profile High, level 1.2
>
> [libx264 @ 00000000025760a0] 264 - core 148 r2762 90a61ec - H.264/MPEG-4 AVC
> codec - Copyleft 2003-2017 - http://www.videolan.org/x264.html - options:
> cabac=1 ref=1 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=2 psy=1
> psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=0 8x8dct=1
> cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=0 threads=7
> 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=1 keyint=30 keyint_min=3 scenecut=40
> intra_refresh=0 rc_lookahead=10 rc=crf mbtree=1 crf=30.0 qcomp=0.60 qpmin=0
> qpmax=69 qpstep=4 vbv_maxrate=96 vbv_bufsize=198 crf_max=0.0 nal_hrd=none
> filler=0 ip_ratio=1.40 aq=1:1.00
>
> Output #0, flv, to
> 'rtmp://***.****.***/live3/yoder?u=gil&e=1492253342&h=32628F7B51A3943A9D57FE
> 1B9D389328':
>
>   Metadata:
>
>     copyright       : Copyright 2017 OABS
>
>     artist          : Gil Yoder
>
>     encoder         : Lavf57.67.100
>
>     Stream #0:0: Video: h264 (libx264) ([7][0][0][0] / 0x0007),
> yuv420p(progressive), 320x240, q=-1--1, 96 kb/s, 15 fps, 1k tbn, 15 tbc
>
>     Metadata:
>
>       encoder         : Lavc57.86.103 libx264
>
>     Side data:
>
>       cpb: bitrate max/min/avg: 96000/0/96000 buffer size: 198000 vbv_delay:
> -1
>
>     Stream #0:1: Audio: aac (LC) ([10][0][0][0] / 0x000A), 11025 Hz, stereo,
> fltp, 24 kb/s
>
>     Metadata:
>
>       encoder         : Lavc57.86.103 aac
>
> [flv @ 000000000259f240] Failed to update header with correct
> duration.7.2kbits/s dup=0 drop=3 speed=1.02x
>
> [flv @ 000000000259f240] Failed to update header with correct filesize.
>
> frame=  936 fps=7.6 q=-1.0 Lsize=    1354kB time=00:02:04.86 bitrate=
> 88.8kbits/s dup=0 drop=3 speed=1.02x
>
> video:949kB audio:363kB subtitle:0kB other streams:0kB global headers:0kB
> muxing overhead: 3.117937%
>
> [libx264 @ 00000000025760a0] frame I:32    Avg QP:25.15  size: 17474
>
> [libx264 @ 00000000025760a0] frame P:253   Avg QP:30.90  size:  1266
>
> [libx264 @ 00000000025760a0] frame B:651   Avg QP:35.10  size:   141
>
> [libx264 @ 00000000025760a0] consecutive B-frames:  7.2%  0.2%  0.3% 92.3%
>
> [libx264 @ 00000000025760a0] mb I  I16..4:  2.3%  5.2% 92.5%
>
> [libx264 @ 00000000025760a0] mb P  I16..4:  0.3%  0.4%  0.3%  P16..4: 33.4%
> 9.0%  7.5%  0.0%  0.0%    skip:49.1%
>
> [libx264 @ 00000000025760a0] mb B  I16..4:  0.0%  0.0%  0.0%  B16..8:  3.5%
> 1.7%  0.2%  direct: 3.8%  skip:90.7%  L0:27.9% L1:42.5% BI:29.6%
>
> [libx264 @ 00000000025760a0] 8x8 transform intra:8.1% inter:14.6%
>
> [libx264 @ 00000000025760a0] coded y,uvDC,uvAC intra: 92.4% 95.3% 88.1%
> inter: 6.0% 6.4% 0.1%
>
> [libx264 @ 00000000025760a0] i16 v,h,dc,p: 50% 20% 18% 13%
>
> [libx264 @ 00000000025760a0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 31% 11% 23%  7%
> 6%  6%  5%  5%  7%
>
> [libx264 @ 00000000025760a0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 30% 20% 10%  5%
> 7%  9%  6%  5%  8%
>
> [libx264 @ 00000000025760a0] i8c dc,h,v,p: 42% 18% 30%  9%
>
> [libx264 @ 00000000025760a0] Weighted P-Frames: Y:43.1% UV:34.8%
>
> [libx264 @ 00000000025760a0] kb/s:62.44
>
> [aac @ 00000000041a8900] Qavg: 645.025
>
>
>
> The actual fps produced is less than desired, but the video doesn't look too
> bad, and the audio sounds okay for voice. Is there a way to improve the A/V
> without increasing bandwidth utilization?
>
>
>
> Gil Yoder
>
>
>
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