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• How do websites render custom videos programatically ?

  18 juillet 2020, par Eric Smith

  I've noticed a number of websites such as https://biteable.com, https://animoto.com/apps/online-video-maker, etc. that are essentially online video editors that allow users to apply effects, add custom text, etc. and render a video as a result.

  


  I've done a bit of research but can't find any high-level answers on how these websites accomplish creating videos programmatically. I've seen mention of "FFmpeg", but this seems like it would only be able to accomplish basic tasks such as converting a series of images into a video (am I wrong ?).

  


  I know very little about video rendering and was hoping someone had an idea to get me started in my research. Are there libraries that exist that can aid to accomplish what these websites are doing ? Or are these websites starting from the ground up with lower-level languages to accomplish this ?

  


• Bash script to automate FFmpeg operations fails when calling the command, but copy-pasting the generated command into the terminal works [duplicate]

  28 février, par GaboScharff99

  I wrote a bash script which automates a number of conversion operations on video files using FFmpeg. Oddly enough, the FFmpeg call itself now fails when running the script, with a very confusing error message, I might add, but when I copy the command generated by the script into the terminal and run it, it works flawlessly. I'm sorry to insert such a long code block here, but considering how strange this error is, it might be anywhere in the script, so here it is :

  


  #!/bin/bash

audioTrack=1
subSource=1
subTrack=0
transcodeVideo=1
transcodeAudio=1
volumeMultiplier=1
degradeToStereo=0
subLanguage="Japanese"

while getopts "t:ns:vam:dl:h" opt; do
    case "$opt" in
        t) audioTrack=${OPTARG};;
        n) subSource=0;;
        s) subTrack=${OPTARG};;
        v) transcodeVideo=0;;
        a) transcodeAudio=0;;
        m) volumeMultiplier=${OPTARG};;
        d) degradeToStereo=1;;
        l) subLanguage=${OPTARG};;
        h)
            echo "Options:"
            echo "-t [integer]: Audio track number. Default: 1."
            echo "-n: If included, subtitles will be taken from internal source."
            echo "-s [integer]: Subtitles track number. Default: 0."
            echo "-v: If included, video source will be copied without transcoding."
            echo "-a: If included, audio source will be copied without transcoding."
            echo "-m [number]: Volume multiplier. If 1, volume is unaffected. Default: 1"
            echo "-d: If included, audio will be degraded to stereo."
            echo "-l [language]: Subtitles language. Only used for external subtitles source. Default: Japanese."
            exit 0
        ;;
    esac
done

echo "Audio track: $audioTrack."
echo "Subtitles track: $subTrack."
params="-map 0:0 -map 0:$audioTrack -map $subSource:$subTrack -c:v"

if [[ $transcodeVideo -eq 1 ]]; then
    echo "Video will be transcoded."
    params="$params hevc"
elif [[ $transcodeVideo -eq 0 ]]; then
    echo "Video will be copied without transcoding."
    params="$params copy"
fi

params="$params -c:a"

if [[ $transcodeAudio -eq 1 ]]; then
    echo "Audio will be transcoded."
    params="$params libopus"
elif [[ $transcodeAudio -eq 0 ]]; then
    echo "Audio will be copied without transcoding."
    params="$params copy"
fi

if [[ $volumeMultiplier -ne 1 ]]; then
    echo "Volume will be multiplied by a factor of $volumeMultiplier."
    params="$params -filter:a 'volume=$volumeMultiplier'"
else
    echo "Volume will be unaffected."
fi

if [[ $degradeToStereo -eq 1 ]]; then
    echo "Audio will be degraded to stereo."
    params="$params -ac 2"
elif [[ $degradeToStereo -eq 0 ]]; then
    echo "Audio will not be degraded to stereo."
fi

params="$params -c:s copy"

if [[ $subSource -eq 1 ]]; then
    echo "Subtitles source is external."
    echo "Subtitles language is $subLanguage."
    params="$params -metadata:s:s:0 title='' -metadata:s:s:0 language='$subLanguage'"
else
    echo "Subtitles source is internal."
fi

if [[ -f titles.txt ]]; then
    echo "A titles.txt file was found. Titles will be changed according to it."
    echo "Please check titles.txt to make sure the titles are correct."
    changeTitles=1
    counter=0
else
    echo "A titles.txt file was not found. Titles will not be changed."
    changeTitles=0
fi

read -p "Are these options correct? (y/n) " choice

case "$choice" in
    y|Y)
        echo "Initiating conversion sequence. This may take a while..."

        mkdir output
        currentParams=""

        shopt -s nullglob
        for i in *.mp4 *.mkv; do
            currentParams=$params
            fileNameNoExtension=$(echo $i | rev | cut -f 2- -d '.' | rev)

            if [[ $subSource -eq 1 ]]; then
                currentParams="-f srt -i $fileNameNoExtension.srt $currentParams"
            fi

            if [[ $changeTitles -eq 1 ]]; then
                ((counter++))
                currentParams="$currentParams -metadata title='$(awk "NR==$counter" titles.txt)'"
            fi

            ffmpeg -i "$i" $currentParams "output/$fileNameNoExtension.mkv"
        done

        echo "Conversion finished!"
    ;;
    n|N) echo "Operation canceled. Exiting.";;
    *) echo "Invalid input. Try again.";;
esac


  


  The directory I'm running this in contains six video files :

  


  

  1. E1 - The Pirates of Orion.mkv

  


  2. E2 - Bem.mkv

  


  3. E3 - The Practical Joker.mkv

  


  4. E4 - Albatross.mkv

  


  5. E5 - How Sharper Than a Serpent's Tooth.mkv

  


  6. E6 - The Counter-Clock Incident.mkv

  


  


  Here's the titles.txt file, for completion's sake :

  


  Star Trek: The Animated Series - Season 2, Episode 1 - The Pirates of Orion
Star Trek: The Animated Series - Season 2, Episode 2 - Bem
Star Trek: The Animated Series - Season 2, Episode 3 - The Practical Joker
Star Trek: The Animated Series - Season 2, Episode 4 - Albatross
Star Trek: The Animated Series - Season 2, Episode 5 - How Sharper Than a Serpent's Tooth
Star Trek: The Animated Series - Season 2, Episode 6 - The Counter-Clock Incident


  


  And finally, here's the error message given by FFmpeg on the terminal for every video file when running the command :

  


  Unable to find a suitable output format for 'Trek:'
Trek:: Invalid argument


  


  Maybe there are better ways to handle all of this, but first and foremost, I would like to figure out why the command fails with such a confusing error message. The only place where the string 'Trek :' is found is in the title taken from titles.txt, but I don't understand why that's seemingly being passed to the name of the output file instead of the title, and apparently only when running the script.

  


  Thanks a lot for your answers ! I know this is quite a bit of text, so I really appreciate you taking your time to read through this.

  


• PHP and FFmpeg : works on terminal but ffmpeg error when in shell_exec

  25 janvier 2014, par user2128983

  I'm in front of a problem I can't solve !

  I try to convert videos using the ffmpeg tool. When I paste the command on the server terminal (ssh root), it works fine. But, when I try in my PHP script using shell_exec, it returns the error "Error while opening encoder ...".

  Here is the command I use :

  ffmpeg -y -i VIDEOIN.mov -preset medium -strict -2 -c:v libx264 -b:v 1000k -pass 1 -f mp4 VIDEOOUT.mp4 null 1>logfile.txt 2>&1 &

  And my PHP script :

  $dir = 'videos/'.$uuid;
  
  $out = $dir.'video.mp4';
  
  $log = $dir.'transcoding_log.txt';
  
  $preset = 'medium';
  
  $bitrate = 1000;
  
  
  
  $cmd = "ffmpeg -y -i ".$in." -preset ".$preset." -strict -2 -c:v libx264 -b:v ".$bitrate."k -pass 1 -f mp4 ".$out." null 1>".$log." 2>&1 &";
  
  @file_put_contents($dir.'cmd.log', $cmd); // to debug
  
  shell_exec($cmd);

  Here is the log file created in the PHP script :

  ffmpeg version 1.0.8 Copyright (c) 2000-2013 the FFmpeg developers
  
  built on Sep 12 2013 11:57:09 with gcc 4.7 (Debian 4.7.2-5)
  
  configuration: --prefix=/usr --extra-cflags='-g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security ' --extra-ldflags='-Wl,-z,relro' --cc='ccache cc' --enable-shared --enable-libmp3lame --enable-gpl --enable-nonfree --enable-libvorbis --enable-pthreads --enable-libfaac --enable-libxvid --enable-postproc --enable-x11grab --enable-libgsm --enable-libtheora --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libx264 --enable-libspeex --enable-nonfree --disable-stripping --enable-libvpx --enable-libschroedinger --disable-encoder=libschroedinger --enable-version3 --enable-libopenjpeg --enable-librtmp --enable-avfilter --enable-libfreetype --enable-libvo-aacenc --disable-decoder=amrnb --enable-libvo-amrwbenc --enable-libaacplus --libdir=/usr/lib/x86_64-linux-gnu --disable-vda --enable-libbluray --enable-libcdio --enable-gnutls --enable-frei0r --enable-openssl --enable-libass --enable-libopus --enable-fontconfig --enable-libfdk-aac --enable-libdc1394 --disable-altivec --dis  libavutil      51. 73.101 / 51. 73.101
  
    libavcodec     54. 59.100 / 54. 59.100
  
    libavformat    54. 29.104 / 54. 29.104
  
    libavdevice    54.  2.101 / 54.  2.101
  
    libavfilter     3. 17.100 /  3. 17.100
  
    libswscale      2.  1.101 /  2.  1.101
  
    libswresample   0. 15.100 /  0. 15.100
  
    libpostproc    52.  0.100 / 52.  0.100
  
  Input #0, matroska,webm, from 'videos/18352678af96ecb5/origin.webm':
  
    Metadata:
  
      creation_time   : 2010-05-20 08:21:12
  
    Duration: 00:00:32.48, start: 0.000000, bitrate: 533 kb/s
  
      Stream #0:0(eng): Video: vp8, yuv420p, 640x360, SAR 1:1 DAR 16:9, 25 fps, 25 tbr, 1k tbn, 1k tbc (default)
  
      Stream #0:1(eng): Audio: vorbis, 44100 Hz, mono, s16 (default)
  
  [libx264 @ 0x19c05a0] using SAR=1/1
  
  [libx264 @ 0x19c05a0] using cpu capabilities: MMX2 SSE2Fast SSEMisalign LZCNT
  
  [libx264 @ 0x19c05a0] ratecontrol_init: can't open stats file
  
  Output #0, mp4, to 'videos/18352678af96ecb5/video.mp4':
  
      Stream #0:0(eng): Video: h264, yuv420p, 640x360 [SAR 1:1 DAR 16:9], q=-1--1, pass 1,     90k tbn, 25 tbc (default)
  
      Stream #0:1(eng): Audio: none, 44100 Hz, mono, s16, 128 kb/s (default)
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (vp8 -> libx264)
  
    Stream #0:1 -> #0:1 (vorbis -> libfaac)
  
  Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as     bit_rate, rate, width or height

  EDIT 1 :

  I compiled ffmpeg with the latest revision but the problem still occurs.