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• React Native and FFMPEG render text differently (Help me)

  6 février 2021, par Douglas Gondim

  I'm creating a video editing app in React Native that allows you to burn subtitles onto any video. I'm facing a problem that the font size on the phone screen doesn't match the font size after the video is rendered.

  


  I can guarantee that the text is being scaled down appropriately on the app side because the video obviously looks smaller on the phone screen than its original size. So the text that I'm placing on top of the video as a preview needs to be scaled down accordingly.

  


  The problem is each different font seems to have a different scale factor when I render the video. So the previewer is ALWAYS off. My solution was to manually scale up/down each font in regards to its approximate width and height factor. But that's a very poor solution.

  


  I assume it has something to do with something called a font.config file that you can set on ffmpeg.

  


  How can I make eg. Arial, 14 in React Native be rendered the same way as Arial, 14 on ffmpeg ? I really need help with that. I don't even know where to look.

  


• can i use -crf and -s option in one command with ffmpeg

  8 octobre 2019, par Trần Tuấn

  I want to create video streaming for phone. To do that i use ffmpeg to convert video into hls. For now i can convert video to hls using this command :

  ffmpeg -y -i video.mp4 -profile:v
  baseline -level 3.0 -crf 51 -start_number 0 -hls_time 10
  -hls_list_size 0 -f hls video.m3u8.

  I know i can reduce video image size by using this command :

  ffmpeg -y -i video.mp4 -profile:v
  baseline -level 3.0 -s 640x360 -r 20 -start_number 0 -hls_time 10
  -hls_list_size 0 -f hls video.m3u8

  can i use both -s and -crf in one command ?
  Because i’m streaming for phone. so size is my main concern.

• H264 decoder in opencv for real time video transmission

  30 mai 2019, par Narendra

  I am writing a client-server application which does real time video transmission from an android based phone to a server. The captured video from the phone camera is encoded using the android provided h264 encoder and transmitted via UDP socket. The frames are not RTP encapsulated. I need it to reduce the overhead and hence the delay.
  On the receiver, I need to decode the incoming encoded frame. The data being sent on the UDP socket not only contains the encoded frame but some other information related to the frame as a part of its header. Each frame is encoded as an nal unit.

  I am able to retrieve the frames from the received packet as a byte array. I can save this byte array as raw h264 file and playback using vlc and everything works fine.
  However, I need to do some processing on this frame and hence need to use it with opencv.
  Can anyone help me with decoding a raw h264 byte array in opencv ?
  Can ffmpeg be used for this ?