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• av::av_encode_video produces blurred video from crisp files

  9 janvier 2023, par Abdirizak

  I am using the av::av_encode_video() function to produce a .mp4 video from png files, as in this answer. I pay special attention for the png files to be perfectly crisp, i.e. I plot matrices to png with exactly the same dimensions, so that every matrix cell maps to one cell in the png. Here is code to illustrate what I mean :

  


  library(av)

n.times <- 24*10
n.row <- 50
n.col <- 26

out.dir <- "/Users/Abdirizak/Documents/some/directory/"

for (i in 1:n.times) {
   
   current.mat <- matrix(data = rnorm(n.row*n.col), nrow = n.row, ncol = n.col)
   
   setwd(out.dir)
   png(filename = paste0(i, ".png"), width = n.row, height = n.col)
   
   par(mar = rep(0,4))
   image(current.mat)
   
   dev.off()
   
}

setwd(out.dir)
png.files <- paste0(out.dir, list.files(pattern = ".png$"))

av::av_encode_video(input = png.files, output = "000.mp4", framerate = 24)


  


  Now, even though my input .png files are perfectly crisp, the output .mp4 video is blurry. How can I prevent that from happening ? I.e. how can I get a perfectly crisp video ? (I am aware that this will likely inflate the file size of the .mp4 file)

  


  I already digged a bit into the vfilter argument of av_encode_video() and the underlying ffmpeg filter graphs on here, but could not yet really get the hang on it.

  


  I am looking at the .mp4 file through QuickTime Player on MacOS Ventura 13.0.1, and using R version 4.2.2 through RStudio 2022.12.0.353

  


  Edit 9.1.2023 :

  


  To further clarify, here is an example screenshot of a png image (not the original png file because that one appears too small here) :

  


  

  


  As I said, a perfectly crisp image.

  


  On the other hand, a screenshot of the .mp4 movie looks like this :

  


  

  


  Somewhat unsatisfactory. Any suggestions are welcome.

  


• ffmpeg video duration is not equal to duration after hls process

  9 décembre 2022, par Timur Khazhiev

  Problem

  


  For videofile input I preprocess/encode it to libx264. Then I'm trying to cut video into 2 second chunks except last one (last one being < 2 seconds) using hls processing

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  ffmpeg -v error -i video.mp4 -x264-params "keyint=60:min-keyint=60:scenecut=0" 
-hls_time 2 -hls_list_size 0 -hls_segment_filename chunk%03d.ts index.m3u8


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  which follows this problem

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  then looking into index.m3u8 file reveals that sum of all chunks' durations does not add up to original video duration :

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  % ffprobe -loglevel quiet -print_format flat -show_entries format=duration index.m3u8     

format.duration="204.880000"

% ffprobe -loglevel quiet -print_format flat -show_entries format=duration video.mp4 

format.duration="204.892813"


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  Moreover duration of a chunk in index.m3u8 is not the same as in chunk file.

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  % ffprobe -loglevel quiet -print_format flat -show_entries format=duration chunk000.ts

format.duration="2.023222"

% cat index.m3u8
#EXTM3U
#EXT-X-VERSION:3
#EXT-X-TARGETDURATION:2
#EXT-X-MEDIA-SEQUENCE:0
#EXTINF:2.000000,
chunk000.ts
#EXTINF:2.000000,
chunk001.ts
#EXTINF:2.000000,
chunk002.ts
...


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  Misc

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  Used these videos : Me at the zoo and I finally found a useful monorail.

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  OS : macos Monterey 12.3.1 (21E258)

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  ffmpeg version 5.1.2 Copyright (c) 2000-2022 the FFmpeg developers
built with Apple clang version 14.0.0 (clang-1400.0.29.102)
configuration: --prefix=/usr/local/Cellar/ffmpeg/5.1.2 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox
libavutil      57. 28.100 / 57. 28.100
libavcodec     59. 37.100 / 59. 37.100
libavformat    59. 27.100 / 59. 27.100
libavdevice    59.  7.100 / 59.  7.100
libavfilter     8. 44.100 /  8. 44.100
libswscale      6.  7.100 /  6.  7.100
libswresample   4.  7.100 /  4.  7.100
libpostproc    56.  6.100 / 56.  6.100


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  What I tried

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  &#xA;
  • Preprocess/transcode video before proceeding with hls

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  • Force keyframes before proceeding with hls

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  • Use 1, 3, 4 seconds chunks

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  • Use different GOP sizes

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  • -hls_flags split_by_time

  &#xA;

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  but it leads to same result or very unequal chunks

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  Questions

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  &#xA;
  1. Is it ok or I'm missing something ?

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  2. If not, what parameters/options should I use to force chunks to be precisely 2 seconds ?

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• Attempting to encode .png images to video format .avi. Getting an output error

  23 janvier 2023, par Trey King

  Here is the problem. My code is :

  &#xA;

  cat *.png | ffmpeg -framerate 30 -f image2pipe -i -c:a copy -c:v libx264 -crf 18 -preset veryslow - output.avi


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  output is :

  &#xA;

  ffmpeg -framerate 30 -f image2pipe -i -c:a copy -c:v libx264 -crf 18
-preset veryslow - output.avi ffmpeg version 5.1.2-essentials_build-www.gyan.dev Copyright (c) 2000-2022 the FFmpeg developers   built with gcc 12.1.0 (Rev2, Built by MSYS2 project)   configuration: --enable-gpl --enable-version3 --enable-static
--disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-lzma --enable-zlib --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-sdl2 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxvid --enable-libaom --enable-libopenjpeg --enable-libvpx --enable-libass --enable-libfreetype --enable-libfribidi --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-ffnvcodec --enable-nvdec --enable-nvenc --enable-d3d11va --enable-dxva2 --enable-libmfx --enable-libgme --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libtheora --enable-libvo-amrwbenc --enable-libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-librubberband   libavutil      57. 28.100 / 57. 28.100   libavcodec     59. 37.100 / 59. 37.100   libavformat   
59. 27.100 / 59. 27.100   libavdevice    59.  7.100 / 59.  7.100   libavfilter     8. 44.100 /  8. 44.100   libswscale      6.  7.100 / 
6.  7.100   libswresample   4.  7.100 /  4.  7.100   libpostproc    56.  6.100 / 56.  6.100
-c:a: Protocol not found Did you mean file:-c:a?


  &#xA;

  I am not sure how to proceed.

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  A one liner that I found elsewhere.

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