[FFmpeg-user] Drawtext - complex expression to show feet+frames

[Mark Burton]

> On 11 Apr 2017, at 21:13, Moritz Barsnick <barsnick at gmx.net> wrote:
> 
> On Tue, Apr 11, 2017 at 19:36:36 +0100, Mark Burton wrote:
>> New here, hope this is an appropriate question layout...
> 
> To start things off, we always prefer to see the (or an example of an)
> actual ffmpeg command line and its complete, uncut console output. I'll
> show you why below.

Sorry about that, looking around the list I didn’t see many doing that so I left it out, but absolutely will do in future. Here is the full output of the original command (which used ’t’).

ffmpeg version N-85343-gd0a3143-tessus Copyright (c) 2000-2017 the FFmpeg developers
  built with Apple LLVM version 8.0.0 (clang-800.0.42.1)
  configuration: --cc=/usr/bin/clang --prefix=/opt/ffmpeg --extra-version=tessus --enable-avisynth --enable-fontconfig --enable-gpl --enable-libass --enable-libbluray --enable-libfreetype --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopus --enable-libschroedinger --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-libzmq --enable-libzvbi --enable-version3 --disable-ffplay --disable-indev=qtkit
  libavutil      55. 60.100 / 55. 60.100
  libavcodec     57. 92.100 / 57. 92.100
  libavformat    57. 72.100 / 57. 72.100
  libavdevice    57.  7.100 / 57.  7.100
  libavfilter     6. 84.100 /  6. 84.100
  libswscale      4.  7.100 /  4.  7.100
  libswresample   2.  8.100 /  2.  8.100
  libpostproc    54.  6.100 / 54.  6.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'in.mov':
  Metadata:
    major_brand     : qt  
    minor_version   : 537199360
    compatible_brands: qt  
    creation_time   : 2017-04-11T17:11:18.000000Z
    timecode        : 01:00:00:00
  Duration: 00:01:00.00, start: 0.000000, bitrate: 118696 kb/s
    Stream #0:0(eng): Video: dnxhd (DNXHD) (AVdn / 0x6E645641), yuv422p(tv, bt709/unknown/unknown), 1920x1080, 116391 kb/s, SAR 1:1 DAR 16:9, 24 fps, 24 tbr, 24k tbn, 24k tbc (default)
    Metadata:
      creation_time   : 2017-04-11T17:11:18.000000Z
      handler_name    : Apple Alias Data Handler
      encoder         : Avid DNxHD Codec
    Stream #0:1(eng): Audio: pcm_s24le (in24 / 0x34326E69), 48000 Hz, stereo, s32 (24 bit), 2304 kb/s (default)
    Metadata:
      creation_time   : 2017-04-11T17:11:18.000000Z
      handler_name    : Apple Alias Data Handler
    Stream #0:2(eng): Data: none (tmcd / 0x64636D74) (default)
    Metadata:
      creation_time   : 2017-04-11T17:11:32.000000Z
      handler_name    : Apple Alias Data Handler
      timecode        : 01:00:00:00
Stream mapping:
  Stream #0:0 -> #0:0 (dnxhd (native) -> mjpeg (native))
Press [q] to stop, [?] for help
[swscaler @ 0x7fe116012800] deprecated pixel format used, make sure you did set range correctly
Output #0, mov, to 'out.mov':
  Metadata:
    major_brand     : qt  
    minor_version   : 537199360
    compatible_brands: qt  
    timecode        : 01:00:00:00
    encoder         : Lavf57.72.100
    Stream #0:0(eng): Video: mjpeg (jpeg / 0x6765706A), yuvj422p(pc), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 24 fps, 12288 tbn, 24 tbc (default)
    Metadata:
      creation_time   : 2017-04-11T17:11:18.000000Z
      handler_name    : Apple Alias Data Handler
      encoder         : Lavc57.92.100 mjpeg
    Side data:
      cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: -1
frame= 1440 fps=148 q=4.0 Lsize=  210807kB time=00:00:59.95 bitrate=28802.1kbits/s speed=6.18x    
video:210798kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.004177%

>> I’ve been trying to learn more about expression evaluation and some
>> of the more complex aspects of controlling drawing text.
> 
> Good job so far!

It really is amazing how powerful this part of ffmpeg is, what you have given me below is quite astounding!

> 0+00
>> 0+01
>> 0+02
>> 0+03
>> 0+04
>> 0+05
>> 0+06
>> 0+07
>> 0+08
>> 0+09
>> 0+10
>> 0+11
>> 0+12
>> 0+13
>> 0+14
>> 0+15
>> 1+00
>> 1+01
>> … and so on.
> 
> Mathematically, the first part is the frame number divided by 16
> (rounded down to integer), the second part the frame number modulo 16 -
> is that right?

Yes, thats correct.

>> drawtext=fontsize=80:fontcolor=white:fontfile=$fontFile:text='%{eif\:0+(t/((1/24)*16))\:d}':x=(w/2)-text_w:y=(h-text_h)/2,
>> drawtext=fontsize=55:fontcolor=white:fontfile=$fontFile:text='+':x=(w/2)+5:y=(h-text_h)/2" \
> [...]
>> The first drawtext for the feet value is 99% accurate, but sometimes
>> it does not change to the next number of the exact frame it should.
> 
> This is where the output from your ffmpeg command comes in handy. It
> would/might tell us the actual framerate. My guess is it's 23.976, or
> more precisely 24000/1001, and not 24. That would explain the slight
> offset.

I am true 24fps, not 23.976. Now that your expression uses frame_num though, I don’t think this will be an issue will it.

>> Is there a way to use a per frame value instead of ’t’?
> You did obviously read the documentation. :-) You seem to have missed
> the expression variable "n, frame_num" though.

You sort of got me! I’ve been using ’n’ for straight forward frame count burnins in my other setups, but I couldn't see a way to use this for the feet and frame counter.

>> Any advice on where to begin with the frames counter. It needs to
>> start at 0, count on every frame to 15 and then restart at 0 on the
>> next frame.
> 
> The frame counter is 'n', it starts at zero, as documented. The rest is
> just math, as explained above. This is called a "modulo operation". The
> expression evaluation for "text" also supports the modulo operation:
> mod(n,16).
> 
> To achieve what you desire, I used:
> $ ffmpeg .... -vf "drawtext=fontsize=80:fontcolor=white:text='%{eif\:n/16\:d}+%{eif\:mod(n,16)\:d}'" [...]
> 
>> Lastly (perhaps I’m dreaming here!) could this theoretically all be
>> combined into a single expression with ability to set the starting
>> counter to 12+06 for example and have it count accurately from there?
>> Had to ask!
> 
> Stop dreaming:
> "12+6" is 198 (12*16+6) higher, just add that to 'n':
> $ ffmpeg .... -vf "drawtext=fontsize=80:fontcolor=white:text='%{eif\:(n+198)/16\:d}+%{eif\:mod((n+198),16)\:d}" […]

This is amazing, I’m blown away by how you have solved everything in one very neat line. I can’t thank you enough for taking the time to respond in such good detail and providing a solution beyond what I expected was possible.

> I haven't figured out how to format "12+6" as "12+06" though. Good luck
> trying! :) (I know how to fake it, but there may be a proper way with
> formatting expressions.)

Yes, thats really the only thing left to do here - I was looking at how this could work and did wonder if the same principles that apply to printf could be applied, but having tried a few variations of ‘d', it seems not. Hmm.

Thank again Moritz, this is huge for me!

Kind regards
Mark