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• How to optimize video to animated GIF conversion using PHP + shell commands

  15 mars 2012, par user1070798

  I have a web application that converts any video into an animated GIF. The app runs in PHP and the following steps are executed through php's shell_exec :

  1. Scale video to smaller dimensions, if they are large (ffmpeg -i $in -s 200x150 -an $out)
  2. Use ffmpeg to extract 1 jpeg every x seconds (ffmpeg -i $in -ss $ss -vframes 1 $out)

  3. Convert jpegs to animated GIF using imagick (convert -delay $delay -loop 0 $dir/* $out)

     aside - the reason I don't use the ffmpeg gif89a output is because the quality sucks.

  I want to be able to except any major image format, but the most common will probably be .flv (flash) and .avi/.mpg.

  My application runs fine, but I am a perfectionist and it needs to be faster for scalability.

  My web server has 16 cores and I would like to utilize them as much as possible, but .flv multi-threading appears to not be supported by ffmpeg, while .avi and some others are supported. Also, ffmpeg doesn't support multi-threading when outputting to jpegs.

  Does anyone know of any other programs that support multi-threading for .flv and others ? Are there any more efficient methods to create an animated GIF from video, while maintaining relatively decent quality (aka not the 100-color palette that ffmpeg supports) ?

  Also, if anyone knows which codecs might perform best for stages 1 and 2, particularly with flv, I'd love to know. I've done hours of testing, but there are just so many options I haven't come to any solid conclusions.

  ***Update : My online app is working well so far animated gif generator. I would still love to make it faster though, so if anyone has run into similar circumstances... let me know !

• How to quantify and compare video quality

  24 mars 2015, par user940154

  I have a set of uncompressed videos in YUV format.

  I have obtained several derived copies in various formats and resolutions from these yuv files using FFmpeg transcoding. (YUVs ----> X Derived Copies)

  What I have also done is, transcode the yuv’s into same resolution AVIs, and now obtained the same set of derived (transcoded) videos treating the AVIs as master. (AVIs ----> X Derived Copies)

  Now I wish to compare the quality of transcoded videos, when derived from AVIs to those derived from YUVs.

  Is there any way for me to do this using FFmpeg. How ? If not, can you please suggest some good open source software to do this.

  Thanks

• FFMPEG Audio, video out of sync

  5 mars 2012, par geeknizer

  I'm creating Video using FFMPEG from pngs. The problem is on creating the video, and combining with video, its never in sync.

  Create video :

  ffmpeg -i /home/ubuntu/pngs/* -vcodec libvpx -r 25 -b 1024k -y video.avi

  generate audio

  ffmpeg -y -f s16le -ar 44100 -ac 2 -i wav_file.wav -acodec libvorbis video.avi

  these snapshots were taken at 25fps from a video. Audio is also extracted from same source.