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av::av_encode_video produces blurred video from crisp files
9 janvier 2023, par AbdirizakI 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 ofav_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.


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Mac El Capitan can't open ffmpeg output with quicktime
12 novembre 2019, par kilojoulesQuicktime can’t read the output of
ffmpeg
when I try making an animation. It uploads to imgur and plays no problem. A previous thread recommended that I add the-pix_fmt yuv420p
flag. But, on my system, that does not work.ffmpeg
runs without error when I exclude thepix_fmt
flag, but I cannot open the output animation in quicktime.Why won’t quicktime open the animation ? How can I make the animation open with quicktime ?
$ ffmpeg -y -i animation/tigers_${ii}_%05d.png -pix_fmt yuv420p tiger${ii}.mp4
ffmpeg version 4.0.2 Copyright (c) 2000-2018 the FFmpeg developers
built with Apple LLVM version 8.0.0 (clang-800.0.42.1)
configuration: --prefix=/usr/local/Cellar/ffmpeg/4.0.2 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-gpl --enable-libmp3lame --enable-libx264 --enable-libxvid --enable-opencl --enable-videotoolbox --disable-lzma
libavutil 56. 14.100 / 56. 14.100
libavcodec 58. 18.100 / 58. 18.100
libavformat 58. 12.100 / 58. 12.100
libavdevice 58. 3.100 / 58. 3.100
libavfilter 7. 16.100 / 7. 16.100
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 1.100 / 5. 1.100
libswresample 3. 1.100 / 3. 1.100
libpostproc 55. 1.100 / 55. 1.100
Input #0, image2, from 'animation/tigers_1.10_%05d.png':
Duration: 00:00:08.32, start: 0.000000, bitrate: N/A
Stream #0:0: Video: png, rgba(pc), 2023x3036 [SAR 17716:17716 DAR 2023:3036], 25 fps, 25 tbr, 25 tbn, 25 tbc
Stream mapping:
Stream #0:0 -> #0:0 (png (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[libx264 @ 0x7fdd7b800c00] width not divisible by 2 (2023x3036)
Error initializing output stream 0:0 -- Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height
Conversion failed!