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• Adjusting PTS when switching between streams

  5 septembre 2017, par Ruben Sanchez Castellano

  My application needs to switch between two (or more) streams at the input while there is only one output (you could think about as a stream multiplexer). The frames from the input are decoded and then re-encoded again due to an overlay stuff.

  So to arrange the AVFrame PTS I calculate an interval before encoding the frames. But the thing is when I switch between a RTMP stream and a MP4 file, the video is delayed a bit every time I switch. So, at the third switch the resulting stream is out of sync.

  I don’t know if I’m missing something I have to modify on the frame before encoding. I also though about creating an independent PTS for frames at the output but I don’t know how to create it.

  The input streams could have different FPS, timebases or codecs and the application must be able to deal with all of them.

• Is it possible to create new mp4 file from a single streaming byte range chunk ?

  11 janvier 2021, par bevinlorenzo

  If I have a remote mp4 file on a server that supports Byte Ranges, is it possible to retrieve a single byte range and create a new/self-contained mp4 from that range data ?

  



  If I try and write a returned byte range data directly to an mp4 file using fs.createWriteStream(remoteFilename) it doesn't get the video meta data (duration, dimensions, etc) that it needs to be playable.

  



  When I get a byte range that starts with 0 and ends with XX the output mp4 is playable, but will have the duration meta-data of the entire video length and will freeze the screen when the byte range is done for the remainder of the duration time.

  



  How else can I take a byte range and create a stand-alone .mp4 file from that stream object ?

  



  The whole point of this is to avoid downloading the entire 10 minute file before I can make a 5 second clip using ffmpeg. If I can calculate and download the byte range, there should be a way to write it to a standalone mp4 file.

  



  Thanks in advance for any help you can provide.

  


• FFmpeg - feeding output of encode operation to filter

  21 août 2017, par nsp

  I wanted to know if we can feed the output of an encode operation to a "filter_complex" with a command like :

  ffmpeg -i input.mp4 -c:v libx264 -s:v 1920x1080 -b:v 10000k "[encoder-output-1]" \
  
  -c:v libx264 -s:v 1280x720 -b:v 5000k "[encoder-output-2]" \
  
  -c:v libx264 -s:v 640x360 -b:v 2000k "[encoder-output-3]" \
  
  -filter_complex "[encoder-output-1][0:v]psnr" -f null - \
  
  -filter_complex "[encoder-output-2][0:v]psnr" -f null -\
  
  -filter_complex "[encoder-output-3][0:v]psnr" -f null - 

  If we can do something like this, how should one name the output pad of the encoder, so that one can reference/map it in the filter_complex
  If not, please let me know what is the easiest way to achieve something like this.

  Note :

  1. I would be using third party encoders that don’t have the capability to calculate PSNR scores internally. Thus, I would like to compute the PSNR within an FFmpeg filter.