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• Incorrect height for U and V channel when creating video from jpgs using ffmpeg

  27 juillet 2022, par Chu Bun

  I use the method in the ffmpeg source sample decode_video.c to decode a series of jpgs into AVFrames. Then use the method in the sample encode_video.c to combine the AVFrames into a video file.

  


  AV_CODEC_ID_MJPEG is used to set up the decoder for the jpgs. The output frames have the format AV_PIX_FMT_YUVJ422P which has (full-width x full-height) Y-channel, and (half-width x full-height) U and V channels. The problem is when I try to encode the frames, ffmpeg seems to expect (half-width x half-height) U and V channels. As a result the colors are stretch in the vertical direction and do not match with the image in the Y-channel.

  


  I could not figure out how to either decode the jpgs into YUV420 (half-width x half-height) frames, or encode frames in YUV422 format. Any pointers ?

  


• Swift : How can I generate Mp4 video from programmaticall output ? [closed]

  21 août 2020, par Mount Ain

  This question is specifically to Swift programming language for Linux & macOS platforms.To understanding the concept, I used Swift programming language. But not depend on Swift programming language. C or C++ is also good to me.

  


  I can generate JPEG image from NSView by using NSBitmapImageRep. But Linux I don't what I want to do. So, the first thing I need to know is the step to generate JPEG image by programmatically without using the NSView. I really don't know How hard it is. But I want to learn how it's work. I feel It's the way to fill the color into pixels one by one to combine a Image. But I don't know How to do in programming. I knew the same way is used in videos by packing the series of image with audio & subtitle & other meta info.

  


  If you ask about compression, I really want to know How Twitter & YouTube compressing uploaded videos without loss of quality.

  


  So what is the concept,

  


  

  1. To generate a JPEG image by programmatically without using NSView ?

  


  2. To generate MPEG-4 video by group of JPEG images ?

  


  


  Thanking in advance...

  


• Flash player seek not working when ffmpeg encoded with gop(-g) = 1 [migrated]

  3 mars 2015, par Brian

  I am trying to deliver video content with frame-by-frame viewing via the SMP Flash player. For encoding, I am using FFMPEG with the x264 video codec for files with .mp4 containers. I am using the latest ffmpeg build and using the OSMF SMP flash video player.

  I am taking a series of png files and creating a .mp4 file :

  ffmpeg -nostdin -loglevel warning  -i out.%d.png -g 1 -crf 15 -c:v libx264 -movflags faststart -pix_fmt yuv420p -r 24 out.mp4

  By encoding with the gop(-g) flag = 1, I am encoding to make each frame a keyframe. When I seek using the scrub bar of the SMP flash player, it always seeks to the start of the video. If I play and scrub/seek the video using the default HTML player, it works perfectly.

  When I encode with the gop(-g) flag = 2, the SMP Flash player scrubs/seeks and plays correctly.

  It looks like there may be some kind of bug or incompatibility with the Flash player. I have found this problem mentioned back in 2009. I think my only hope is to find a work around. Any suggestions ?