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• 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 ?

• Get PTS from raw H264 mdat generated by iOS AVAssetWriter

  26 décembre 2012, par kolyuchiy

  I'm trying to simultaneously read and write H.264 mov file written by AVAssetWriter. I managed to extract individual NAL units, pack them into ffmpeg's AVPackets and write them into another video format using ffmpeg. It works and the resulting file plays well except the playback speed is not right. How do I calculate the correct PTS/DTS values from raw H.264 data ? Or maybe there exists some other way to get them ?

  Here's what I've tried :

  1. Limit capture min/max frame rate to 30 and assume that the output file will be 30 fps. In fact its fps is always less than values that I set. And also, I think the fps is not constant from packet to packet.

  2. Remember each written sample's presentation timestamp and assume that samples map one-to-one to NALUs and apply saved timestamp to output packet. This doesn't work.

  3. Setting PTS to 0 or AV_NOPTS_VALUE. Doesn't work.

  From googling about it I understand that raw H.264 data usually doesn't contain any timing info. It can sometimes have some timing info inside SEI, but the files that I use don't have it. On the other hand, there are some applications that do exactly what I'm trying to do, so I suppose it is possible somehow.

• How to split video to 3 parts by ffmpeg ?

  14 avril 2014, par user3524742

  I want to split video to 3 parts in batch mode. So, I have this code :

  @echo off
  
  for %%i in ("*.mp4") do ffmpeg -i "%%i" -vcodec copy -acodec copy -ss 00:00:00 -t 00:00:05 D:\Ebook\%%~nxi_1.mp4
  
  for %%i in ("*.mp4") do ffmpeg -i "%%i" -vcodec copy -acodec copy -ss 00:00:05 -t 00:00:10 D:\Ebook\%%~nxi_2.mp4
  
  for %%i in ("*.mp4") do ffmpeg -i "%%i" -vcodec copy -acodec copy -ss 00:00:10 D:\Ebook\%%~nxi_3.mp4
  
  pause

  It works but having some problem :
  1. It save file : .mp4_1.mp4. How to remove ".mp4" ?
  2. When filename of video contain space character. It shows error : "Invalid argument". How to fix it ?

  Thank you very much !