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• How to create a DASH VOD for Chromecast with ffmpeg ?

  19 novembre 2020, par Oleg Yablokov

  I need to serve long videos ( 2 hours) from a web server to mobile clients and the clients should be able to play the videos via Chromecast. I have chosen mpeg-dash for this purpose : video encoder is h.264 (level 4.1), audio is aac (although I've tried diffrent ones).

  


  I've tried ffmpeg, MP4Box and some other tools to generate videos ; most of the time I succeeded playing them on VLC or on a mobile client (locally), but not with Chromecast.

  


  I've tried Amazon's Elastic Transcoder and it worked, but it gave me one big file whereas I need many small segments.

  


  CORS are set.

  


  Chromecast remote debugging didn't help much.

  


  Do you know how to do this ?

  


• why ffmpeg starts many processes

  29 octobre 2020, par james

  I have a doubt about the functioning of the ffmpeg program, I noticed that after starting the program on a 4gb memory raspberry pi4 many processes are started, is it normal or is there something wrong with my program ? I remember that on an amazon ec2 instance by controlling with htop only one process was created

  


  Code I used

  


  from subprocess import Popen

ffmpeg_process = Popen(["ffmpeg", "-hide_banner", "-loglevel", "panic", "-y", "-i", "./video/video1.mp4",
                        "-vcodec", "h264", "-acodec", "mp3", "./video/video2.mp4"],
                        start_new_session=True)

ffmpeg_process.wait()


  


  

  


• FFMPEG H264 with custom overlay per frame

  4 octobre 2020, par La bla bla

  We have a stream that is stored in the cloud (Amazon S3) as individual H264 frames. The frames are stored as framexxxxxx.264, the numbering doesn't start from 0 but rather from some larger number, say 1000 (so, frame001000.264)

  


  The goal is to create a mp4 clip which is either timelapse or just faster for inspection and other checking (much faster, compressing around 3 hours of video down to < 20 minutes), this also requires we overlay the frame number (the filename) on the frame itself

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  At first I was creating a timelapse by pulling from S3 only the keyframes (i-frames ? still rather new to codecs & stuff) and overlaying the filename on them and saving as png (which probably isn't needed, but that's what I did) using (this command is used inside a python script)

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  ffmpeg -y -i {h264_name} -vf \"scale=1920:-1, 
drawtext=fontfile=/usr/share/fonts/truetype/ubuntu-font-family/Ubuntu-B.ttf:fontsize=34:text={txt}:fontcolor=white:x=50:y=50:bordercolor=black:borderw=2\" 
-c:a copy -pix_fmt yuv420p {basename}.png


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  after this I combined all the frames by using python to convert the lowest numbered frame to 0.png and incrementing (so it would be continuous, because I only used keyframes the numbers originally weren't sequential) and running

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  ffmpeg -y -f image2 -i %d.png -r {self.params.fps} -vcodec libx264 -crf {self.params.crf} -pix_fmt yuv420p {out_file}


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  and this worked great, but the difference between keyframes was too long to allow for proper inspection

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  so now for the question(s)

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  since I know frames that are not keyframes (p-frames ?) can't be used alone by ffmpeg, the method of overlaying the file name and converting it to png (or keep as h264, same thing) won't work, or at least, I couldn't find a way for it to work, maybe there's a way to specify a frame's keyframe ?, how can one overlay the filename (and not the frame number as shown here for example)

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  Also, is it possible to skip some p-frames between the keyframes ? (so if a keyframe is every 30 frames, we would take a keyframe, a frame 15 frames later, and next another keyframe)

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  I thought about using ffmpeg's pipe option to feed it with the files as they're being downloaded, but I'm not sure if I can specify drawtext this way

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  Also, if there's another alternative that can achieve that (at first I was converting to png, using python and OpenCV to add the filename and then merging the pngs to mp4, but then I found drawtext can do that in a single command so I used it)

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