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• Screencasting with hardware-accelerated gnome-3 [closed]

  30 octobre 2012, par Jeroen

  I am running Ubuntu 12.04 with gnome 3 shell, and I would like to create a screencast. I have tried using recordMyDesktop, Kazam Screencaster, and ffmpeg but all suffer from the same problem, which I think has to do with hardware acceleration in Gnome 3. The recorded videos all get very glitchy with blue space for all operations that use some sort of effect. Here is an example recording : http://www.stat.ucla.edu/ jeroen/files/screencast.mkv.

  The only method that does not seem to suffer from this, is the (largely undocumented) CTRL+SHIFT+R shortcut in gnome 3 that will start a recording. However, this feature is very buggy otherwise and often crashes when I enable audio input.

  My machine has a GeForce GT 120 with Apple LED Cinema monitor. I am using the proprietary nvidia drivers that ship with Ubuntu 12.04. Is there any way I can record the video as it appears on my screen ? I know I can avoid the problem by switching to gnome2 or unity 2d or anything that does not use effects, but I would prefer to make the recordings in my regular gnome 3 environment.

• Best Web Video Encoding Practices for IOS (FFMpeg)

  21 juin 2012, par MagicMushroom

  I am working on an online video repository system for a client, written mostly in PHP. At the moment I am building a mobile version of our desktop website. Our desktop site allows users to watch videos in the browser, much like YouTube.

  My client uploads videos through the manager interface I have created, and my application uses FFmpeg on the server to transcode his videos into several resolutions and bitrates. I am no expert on FFmpeg, and while I do not know the ins and outs of each individual setting, I do understand how it works as a whole. Right now, we are using the mp4 container format with the h.264 codec to encode our videos. Our command looks like :

  ffmpeg -y -i "INPUT FILE.mov" -f mp4 -s 640x480 -vcodec libx264 -preset fast -maxrate 1500 -bitrate 1000 -bufsize 4096 -acodec libfaac -ab 192 -ac 2 "OUTPUT_FILE.mp4" >> "FILE.log" 2>&1 &

  I'm hoping to gain information about best practices with encoding video for web streaming on IOS and other mobile devices using FFmpeg. What resolutions and settings make for good mobile streaming video ? How can I ensure maximum compatibility across the sea of Android devices ?

• 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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  • 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

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  but it leads to same result or very unequal chunks

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  Questions

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  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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