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• -12909 error decoding h264 stream with intra-refresh

  2 juillet 2024, par ciclopez

  I'm making an iOS app that decodes an h264 stream using video-toolbox. I create the stream with ffmpeg on a PC and send it to an iPhone using RTP. It's working nicely when I use this command to create it :

  



  ffmpeg -y -f:v rawvideo -c:v rawvideo -s 1280x720 -pix_fmt bgra -r 30 -an -i - -pix_fmt yuv420p -c:v libx264 -tune zerolatency -preset fast -b:v 5M -refs 1 -g 30 -profile:v high -level 4.1 -f rtp rtp://192.168.1.100:5678


  



  The iPhone receives and displays all the frames. However, when I enable intra-refresh

  



  -intra-refresh 1


  



  decoding fails with error code -12909 (-8969 on simulator) when VTDecompressionSessionDecodeFrame() is called.

  



  I take care of processing UDP packets to extract NAL Units, so I triple checked this process and discarded a problem with this part of the code.

  



  I didn't find any info about Video-toolbox not supporting intra-refresh, so the question is, does Video-toolbox support intra-refresh ? and if it does, am I missing something in the ffmpeg side that makes the stream not supported by Video-toolbox ?
Do I have to add something to the CMVideoFormatDescriptionRef apart from creating it with SPS and PPS data using CMVideoFormatDescriptionCreateFromH264ParameterSets() ?

  


• How To Concatenate Two MP4 Videos With Different Aspect Ratios and Resolutions

  11 novembre 2017, par PortableDiag

  I am using ffmpeg to concatenate multiple MP4 videos, two at a time. The problem I am having is that the videos are often different resolutions and aspect ratios. One might come from a 480p webcam with a 1:1 aspect ratio and the other a brand new iPhone with 4k video and rectangular aspect ratio. Currently I must choose and set the aspect ratio manually and this results in one of the two videos becoming distorted, depending on the selected aspect ratio.

  How can I merge two videos so that the overall viewing field has a square aspect ratio but videos with a rectangular aspect ratio will be scaled to fit inside.

  I am using this command to merge the videos :

  ffmpeg -threads 1 -i '/518.mp4' -i '/516.mp4' -y -filter_complex "[0:v]scale=1080x1920,setpts=PTS-STARTPTS,setdar=0/1[v0];[1:v]scale=1080x1920,setpts=PTS-STARTPTS,setdar=0/1[v1];[v0][0:a][v1][1:a]concat=n=2:v=1:a=1" '/partial1.mp4'

  This is the result : https://www.dropbox.com/s/x1un7z1ljwr6tty/merged_newsort.mp4?dl=0

  Is it possible to apply a border to the rectangular video to give them a square aspect ratio ?

  How can I keep prevent distortion from occurring during the merge process ?

  Thanks in advance.

• HEVC video cutting issues using FFmpeg

  4 novembre 2017, par Dmitry Katkevich

  I need to cut videos using FFmpeg and I cannot transcode original videos (because of the performance reason). And I ran into a problem with HEVC videos from IPhone : there are glithes in the beginning of the cutted video.

  Here is how we converted videos before issue :

  ffmpeg.exe -i original.MOV -c:v copy -c:a aac -ss 4 -y good.mp4

  But for HEVC video there are glitches for 1 second in the beginning of the cutted video :

  

  Then I’ve tried to put seek option before input video :

  ffmpeg.exe -ss 4 -i original.MOV -c:v copy -c:a aac -y good.mp4

  The result seems good :

  

  After some googling it turns out that -ss option before input is faster but less accurate whereas -ss option after input and before output is slower but more accurate.

  So my questions are :

  • Why -ss option behaves differently then it is put before/after input ?

  • Is there a way to avoid glitches using output seek ffmpeg option ?

  • What does ’more/less accurate’ mean ? Does it mean that the seek may be too big or to little (bigger/less than we specified) ? How big may be this difference ?