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• How can I automate video encoding using FFmpeg

  30 janvier 2020, par park joh

  I want to find the optimal encoding for a video using FFmpeg and looking for a script to automate that.

  there is VMAF (libvmaf) that helps us to measure the quality of the results, I look for a script or a way to use it to decide what is the best flags to encode each video based on libvmaf score.

  For example, I want to get a list of :
  FFmpeg (flag list and values), VMAF score, total size, average bitrate, max bitrate, min bitrate

  Then I would be able to choose the encoding flags based on that list and my bitrate preference.

  Do anyone know how to compose that kind of a script/ direct me to exist one (or existing flag of FFmpeg that I don’t know that do exactly that...)

• avcodec/atrac9dec : Don't confuse max_depth of VLC with max codelength

  4 novembre 2020, par Andreas Rheinhardt

  avcodec/atrac9dec : Don't confuse max_depth of VLC with max codelength
  The whole point of VLCs with their tables is to read more than one bit
  
  at a time ; therefore max_depth, the number of times one has to
  
  (maximally) read further bits is given by ceil(max_code_length / table_bits)
  
  which in the case of ATRAC9's coefficient VLCs gives an upper bound of
  
  two. Instead the maximum length of a code of the given VLC has been used
  
  (which is not even a compile-time constant). Use two instead.
  Furthermore, given that this was the only usage of the field containing
  
  the maximum of all the code lengths of a given VLC the field has been
  
  removed from its containing struct.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavcodec/atrac9dec.c
  • [DH] libavcodec/atrac9tab.h

• ffmpeg video stream delay in playback ?

  22 février 2017, par user685869

  I’m trying to capture and stream video from a 5MP USB camera using ffmpeg 3.2.2 on Windows. Here’s the command line that I’m using :

  ffmpeg -f dshow -video_size 320x240 -framerate 30 -i video="HD USB Camera" -vcodec libx264 -preset ultrafast -tune zerolatency -g 60 -f mpegts udp://192.168.1.100:10000

  The destination for my stream (an Ubuntu box on the same subnet) is running ffplay via :

  ffplay -i udp://127.0.0.1:10000

  This works but the video stream seems like it’s delayed by 8 - 10 seconds. It’s my understanding that the destination can’t begin displaying the stream until it receives an I-frame so I tried specifying a GOP value of 60 thinking that this would cause an I-frame to be inserted every 2 seconds (@ 30 FPS).

  The Windows machine that’s doing the transcoding is running an i7-3840QM @ 2.80GHz and has 32 GB RAM. FFmpeg appears to be using very little CPU (like 2%) so it doesn’t seem like it’s CPU bound. Just as a test, I tried ingesting an MP4 file and not doing any transcoding (ffmpeg -re -i localFile.mp4 -c copy -f mpegts udp://192.168.1.100:10000) but it still takes several seconds before the stream is displayed on the Ubuntu system.

  On a related note, I’m also evaluating a trial version of the Wowza Streaming Engine server and when I direct my ffmpeg stream to Wowza, I get the same 8 - 10 second delay before the Wowza test player starts playing it back. For what it’s worth, once the stream starts playing, it seems to be running fine (other than the fact that everything is "behind" by several seconds).

  I’m new to video streaming so I might be missing something obvious here but can anyone tell me what might be causing this delay or suggest how I might further troubleshoot the problem ? Thank you !