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• Video parameters for best web scrolling performance [duplicate]

  22 février 2018, par biven

  This question already has an answer here :

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  There is web application which provides next workflow. User uploads video -> backend(by using ffmpeg) transform this video for smaller size(320x240) -> web browser plays transformed video. Key feature of this application should be excellent scrolling possibility of video by progress bar. I mean that video should be scrolled as smoothly as possible (without any jumps) when user moves progress bar position back and forward.

  I thought that small size of video helps to provide good scrolling possibility. But that’s incorrect. I have 2 different videos, one scrolling perfect(as I want), second has same resolotion(320x240), but it is scrolling with jumps and breaks.

  By ffprobe I compared both videos and I have next results :

  Video 1(good scrolling) :

  libavutil      56.  7.100 / 56.  7.100
  
    libavcodec     58.  9.100 / 58.  9.100
  
    libavformat    58.  5.100 / 58.  5.100
  
    libavdevice    58.  0.101 / 58.  0.101
  
    libavfilter     7. 11.101 /  7. 11.101
  
    libswscale      5.  0.101 /  5.  0.101
  
    libswresample   3.  0.101 /  3.  0.101
  
    libpostproc    55.  0.100 / 55.  0.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'spacetestSMALL_512kb.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: mp41
  
      creation_time   : 1970-01-01T00:00:00.000000Z
  
      title           : small test video - http://www.archive.org/details/alanoakleysmalltestvideo
  
      encoder         : Lavf51.10.0
  
      comment         : license:  http://www.copyright.gov/
  
    Duration: 00:00:48.32, start: 0.000000, bitrate: 555 kb/s
  
      Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 320x240, 505 kb/s, 25 fps, 25 tbr, 25 tbn, 50 tbc (default)
  
      Metadata:
  
        creation_time   : 1970-01-01T00:00:00.000000Z
  
        handler_name    : VideoHandler
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 45 kb/s (default)
  
      Metadata:
  
        creation_time   : 1970-01-01T00:00:00.000000Z
  
        handler_name    : SoundHandler

  Video 2(bad scrolling) :

  libavutil      56.  7.100 / 56.  7.100
  
    libavcodec     58.  9.100 / 58.  9.100
  
    libavformat    58.  5.100 / 58.  5.100
  
    libavdevice    58.  0.101 / 58.  0.101
  
    libavfilter     7. 11.101 /  7. 11.101
  
    libswscale      5.  0.101 /  5.  0.101
  
    libswresample   3.  0.101 /  3.  0.101
  
    libpostproc    55.  0.100 / 55.  0.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'e10b1c93-5325-4500-ae7c-12ccd0f617bd.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf58.5.100
  
    Duration: 00:00:07.96, start: 0.000000, bitrate: 428 kb/s
  
      Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 320x240 [SAR 4:3 DAR 16:9], 391 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 33 kb/s (default)
  
      Metadata:
  
        handler_name    : SoundHandler

  What is the key parameter of video which provide possibility for good scrolling in web browser ?

• FFMpeg cannot start using Process API

  8 juin 2021, par Prophet Lamb

  So I am trying to use FFProbe to retrieve media information using the Process API, I am on Net 5 and wish to stay cross-platform compatible.
Before I started fiddling around I tried FFMpeg Core to retrieve metadata, but it works only on windows, and cannot handle multiline tags, only the last line is parsed.
So I tried to manually pipe the output to my application.
Initially I've used CliWrap to neatly pipe the output to a StringBuilder as I usually do in other repositories.

  


  var output = new StringBuilder();
var args = new[] { "-i", filePath };
var pResult = await Cli.Wrap(GetFFProbeFilePath())
    .WithArguments(args)
    .WithStandardOutputPipe(PipeTarget.ToStringBuilder(output))
    .ExecuteAsync(cancellationToken);


  


  

  • filePath : any media file.

  


  • GetFFProbeFilePath() : scrubbs %PATH% for ffmpeg, returns "C :\ProgramData\chocolatey\bin\ffprobe.exe".

  


  • cancellationToken : None for test-cases.

  


  


  But that did not work. The output always stays empty.
So I ran the following command using non-elevated cmd : C:\\ProgramData\\chocolatey\\bin\\ffprobe.exe -i my/lovely/file.mp3
and the console displays the output fully, with no error.

  


  Naturally it's the fault of CliWrap cause I am perfect ; that's why I replaced it with a plain Process API call :

  


  var output = new StringBuilder();
using (var p = new Process())
{
    p.StartInfo.FileName = "C:\\ProgramData\\chocolatey\\bin\\ffprobe.exe";
    p.StartInfo.Arguments = String.Join(' ', args);
    p.StartInfo.UseShellExecute = false;
    p.StartInfo.RedirectStandardOutput = true;
    p.Start();
    output.Append(await p.StandardOutput.ReadToEndAsync());
    await p.WaitForExitAsync(cancellationToken);
}


  


  Still the output is empty. So instead of using a pipe that I write to the output of a file :

  


  using var p = new Process();
p.StartInfo.FileName = "C:\\ProgramData\\chocolatey\\bin\\ffprobe.exe";
p.StartInfo.Arguments = " -i \"" + filePath + "\" 2> " + "\"C:\\temp\\metadata.log\"";
if (!p.Start())
    throw new Exception();
await p.WaitForExitAsync(cancellationToken);


  


  

  • C:\temp\ : 777

  


  


  The temporary file is not created, from that I conclude that the process has not exited successfully. Even though no exception is thrown (I tried piping the errors as well : nothing).

  


  Then I proceed to run this command 20x and wonder why it works in ps & cmd, but not in C# :

  


  C:\ProgramData\chocolatey\bin\ffprobe.exe -i  my/lovely/file.mp3 2> "C:\temp\metadata.log"

  


  Until I ran it using [Win]+[R], and I got a graphic glich and Windows Error Reporting instead of the process completing, the file was not created. After some experimenting I found that the same behaviour for start + the command in cmd.

  


  Why in (insert deity of preference) name is there a difference between [Win]+[R] and cmd, and why does it crash when run from C# ? How do I overcome this weird behaviour, while still being cross-platform compatible ?

  


  This entire affair works just fine in linux by the way.

  


  Edit :
When starting the cmd process manually, FFProbe is called correctly, but I still do not retrieve any data on the output pipeline, since cmd.exe doesn't write anything, and I can't pipe FFProbe.

  


  var output = new StringBuilder();
_ = await Cli.Wrap("cmd.exe")
   .WithArguments("/C ffprobe -i \"my/lovely/file.mp3\" 2> \"C:\\temp\\metadata.log\"") 
   .WithStandardOutputPipe(PipeTarget.ToStringBuilder(output))
   .ExecuteAsync(cancellationToken);


  


  This actually creates the metadata.log file, but no output since I only redirect the output of cmd.exe, not ffprobe.
My current thought is, that I could open a conhost and manually pipe the ffprobe output to the console input by providing the pipeline explicitly in the command arguments which again would not work in linux the same way, that kind of defeats the purpose.

  


• Random audio/video sync issue with libcamera-vid + ffmpeg on raspberry pi 3a+

  8 mai, par kepperi

  I have been working on camera software, which will stream live fullhd video to Cloudflare Stream via RTMPS protocol. Everything is mostly working nicely, but I have occasional A/V sync issues with the streams : Stream might start with correct A/V sync and it will stay correct until the end (1-2 h stream), but sometimes the A/V sync is misaligned like 1-2 sec so, that the audio is either behind or ahead of the video stream. And it will be like that until the end of the stream, then next stream might be just fine.

  


  I'm using libcamera-vid for the video and ffmpeg for the audio, muxing and sending all to Cloudflare. This is my command :

  


  libcamera-vid 
  --width 1920 --height 1080 --framerate 30 --timeout 0 
  --nopreview true --inline 1 --codec h264 --verbose 0 
  --intra 90 --bitrate 4000000 --output - | 
ffmpeg 
  -use_wallclock_as_timestamps 1 -loglevel error 
  -probesize 10M -analyzeduration 5M 
  -fflags +genpts -thread_queue_size 512 -f h264 -framerate 30 -i - 
  -thread_queue_size 8192 -itsoffset 0.7 
  -f alsa -channels 1 -ar 44100 -i hw:1,0 
  -c:v copy -c:a aac -b:a 96000 -fflags +genpts -async 1 -shortest -f flv - | 
( sleep 5; ffmpeg -re -i - -c copy -f flv "rtmps://live.cloudflare.com:443/live/..."


  


  So I can control initial A/V sync with -itsoffset and it is working, but still I encounter those random sync differences.

  


  I have also added the second ffmpeg command with 5 sec sleep to give the first ffmpeg process enough time to align with video and audio input before sending them to Cloudflare, but this seems not helping.

  


  I have also tried with Gstreamer, which fixed the AV issue completely, but it had weird glitches on video frames if the audio was enabled. Seemed like it tried to match the audio and video timestamps on fly and that caused warps/jumps and ghost frames on video. Audio was just fine.

  


  Here is my Gstreamer command (which will also have the same libcamera-vid piped in via fdsrc)

  


  GST_CLOCK_SYSTEM=1 gst-launch-1.0 -v
   fdsrc blocksize=524288 !
   h264parse config-interval=1 disable-passthrough=true !
   queue max-size-buffers=200 max-size-time=4000000000 max-size-bytes=0 !
   flvmux name=mux streamable=true latency=200 !
   queue max-size-buffers=200 max-size-time=4000000000 max-size-bytes=0 !
   rtmpsink sync=false location="rtmps://live.cloudflare.com:443/live/..."
   alsasrc device=hw:1,0 buffer-time=1000000 latency-time=200000 !
   audio/x-raw,rate=44100,channels=1,format=S16LE !
   queue leaky=downstream max-size-buffers=500 max-size-time=15000000000 max-size-bytes=0 !
   audioconvert ! audioresample ! avenc_aac bitrate=96000 ! aacparse !
   queue max-size-buffers=100 max-size-time=4000000000 max-size-bytes=0 ! mux.


  


  With Gstreamer, I have been experimenting different sizes of buffers, but no luck getting rid of the video glitches. If I remove audio from that gst-launch-1.0 command, video is just perfect.

  


  Hardware :

  


  

  • RPI 3A+ (tested also with RPI4)

  


  • RPI HQ M12 camera module

  


  • Cheap USB tiny mic (like this : https://www.digikey.fi/fi/products/detail/seeed-technology-co-ltd/114992002/10451894)

  


  


  I have also tried MUX instead of Cloudflare Stream, both acts identically so I guess the problem is not in receiving end encoding. This is also the reason I have not yet tried to "stream" into file.

  


  Currently I'm in a process of testing the libcamera-vid with raw yuv420 + ffmpeg but with ffmpeg encoding the video instead of just having encoded h264 from libcamera-vid. This is done with RPI4 since it has enough CPU for it.

  


  All help is appreciated !