[FFmpeg-user] filterstats broadcast legal report

[Dave Rice]

Hi Carles,

> On Feb 11, 2015, at 1:45 PM, Carles Vila <cvilad at gmail.com> wrote:
> 
> Hi all,
> I'd like to set up a command to find out if a video is broadcast legal.
> I've tried to understand how signalstats works but I need some help.
> I tried the examples in the ffmpeg filter documentation, like the one
> pasted below, but I'd like to customize it to my needs.
> 
> Ideally It would output a list of frames that do not meet broadcast specs.
> 
> FWIW, the video is Quicktime wrapped DNxHD.
> Thank you!
> 
> 
> $ ffprobe -f lavfi movie=INPUTFILE.mov,signalstats="stat=brng" -show_frames
> ffprobe version 2.4.2 Copyright (c) 2007-2014 the FFmpeg developers
>  built on Oct 28 2014 17:39:46 with Apple LLVM version 5.1
> (clang-503.0.40) (based on LLVM 3.4svn)
>  configuration: --prefix=/usr/local/Cellar/ffmpeg/2.4.2 --enable-shared
> --enable-pthreads --enable-gpl --enable-version3 --enable-nonfree
> --enable-hardcoded-tables --enable-avresample --enable-vda --cc=clang
> --host-cflags= --host-ldflags= --enable-libx264 --enable-libfaac
> --enable-libmp3lame --enable-libxvid --enable-libfreetype
> --enable-libtheora --enable-libvorbis --enable-libvpx --enable-librtmp
> --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libvo-aacenc
> --enable-libass --enable-ffplay --enable-libspeex --enable-libschroedinger
> --enable-libfdk-aac --enable-libopus --enable-frei0r --enable-libopenjpeg
> --extra-cflags='-I/usr/local/Cellar/openjpeg/1.5.1_1/include/openjpeg-1.5 '
>  libavutil      54.  7.100 / 54.  7.100
>  libavcodec     56.  1.100 / 56.  1.100
>  libavformat    56.  4.101 / 56.  4.101
>  libavdevice    56.  0.100 / 56.  0.100
>  libavfilter     5.  1.100 /  5.  1.100
>  libavresample   2.  1.  0 /  2.  1.  0
>  libswscale      3.  0.100 /  3.  0.100
>  libswresample   1.  1.100 /  1.  1.100
>  libpostproc    53.  0.100 / 53.  0.100
> Input #0, lavfi, from 'movie=INPUTFILE.mov,signalstats=stat=brng':
>  Duration: N/A, start: 0.000000, bitrate: N/A
>    Stream #0:0: Video: rawvideo (Y42B / 0x42323459), yuv422p, 1920x1080
> [SAR 1:1 DAR 16:9], 25 tbr, 25 tbn, 25 tbc
> [FRAME]
> media_type=video
> key_frame=1
> pkt_pts=0
> pkt_pts_time=0.000000
> pkt_dts=0
> pkt_dts_time=0.000000
> best_effort_timestamp=0
> best_effort_timestamp_time=0.000000
> pkt_duration=1
> pkt_duration_time=0.040000
> pkt_pos=577024
> pkt_size=4147200
> width=1920
> height=1080
> pix_fmt=yuv422p
> sample_aspect_ratio=1:1
> pict_type=I
> coded_picture_number=0
> display_picture_number=0
> interlaced_frame=0
> top_field_first=0
> repeat_pict=0
> TAG:lavfi.signalstats.YMIN=12
> TAG:lavfi.signalstats.YLOW=58
> TAG:lavfi.signalstats.YAVG=74.9742
> TAG:lavfi.signalstats.YHIGH=84
> TAG:lavfi.signalstats.YMAX=241
> TAG:lavfi.signalstats.UMIN=36
> TAG:lavfi.signalstats.ULOW=145
> TAG:lavfi.signalstats.UAVG=150.074
> TAG:lavfi.signalstats.UHIGH=158
> TAG:lavfi.signalstats.UMAX=166
> TAG:lavfi.signalstats.VMIN=47
> TAG:lavfi.signalstats.VLOW=98
> TAG:lavfi.signalstats.VAVG=106.101
> TAG:lavfi.signalstats.VHIGH=112
> TAG:lavfi.signalstats.VMAX=174
> TAG:lavfi.signalstats.SATMIN=0
> TAG:lavfi.signalstats.SATLOW=24
> TAG:lavfi.signalstats.SATAVG=32.6906
> TAG:lavfi.signalstats.SATHIGH=42
> TAG:lavfi.signalstats.SATMAX=99
> TAG:lavfi.signalstats.HUEMED=313
> TAG:lavfi.signalstats.HUEAVG=308.107
> TAG:lavfi.signalstats.YDIF=0
> TAG:lavfi.signalstats.UDIF=0
> TAG:lavfi.signalstats.VDIF=0
> TAG:lavfi.signalstats.BRNG=0.00231144
> [/FRAME]

This means that 0.00231144% of the frame is outside of broadcast range (Y within 16-235 and U/V within 16-240) which in your file is about 4,793 pixels. I vaguely remember someone referring a broadcast standards document  which referred to broadcast legal not considering 100% of pixels to be within that range, but considered broadcast legal to mean somewhat less than 100% of the pixels had to be in the stated ranges. Unfortunately I can't remember what amount of outliers was tolerated or what the spec was.

The output of 
ffprobe -f lavfi movie=INPUTFILE.mov,signalstats="stat=brng" -show_entries frame_tags=lavfi.signalstats.BRNG -of flat

may be easier to parse in your scenario since the output will include the frame numbers, like

frames.frame.567.tags.lavfi_signalstats_BRNG="0"
frames.frame.568.tags.lavfi_signalstats_BRNG="0"
frames.frame.569.tags.lavfi_signalstats_BRNG="0"

then you would need to grep out the lines where BRNG exceed some defined threshold. Hope this helps.
Dave Rice