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• Extract frames as images from an RTMP stream in real-time

  7 novembre 2014, par SoftForge

  I am streaming short videos (4 or 5 seconds) encoded in H264 at 15 fps in VGA quality from different clients to a server using RTMP which produced an FLV file. I need to analyse the frames from the video as images as soon as possible so I need the frames to be written as PNG images as they are received.

  Currently I use Wowza to receive the streams and I have tried using the transcoder API to access the individual frames and write them to PNGs. This partially works but there is about a second delay before the transcoder starts processing and when the stream ends Wowza flushes its buffers causing the last second not to get transcoded meaning I can lose the last 25% of the video frames. I have tried to find a workaround but Wowza say that it is not possible to prevent the buffer getting flushed. It is also not the ideal solution because there is a 1 second delay before I start getting frames and I have to re-encode the video when using the transcoder which is computationally expensive and unnecessarily for my needs.

  I have also tried piping a video in real-time to FFmpeg and getting it to produce the PNG images but unfortunately it waits until it receives the entire video before producing the PNG frames.

  How can I extract all of the frames from the stream as close to real-time as possible ? I don’t mind what language or technology is used as long as it can run on a Linux server. I would be happy to use FFmpeg if I can find a way to get it to write the images while it is still receiving the video or even Wowza if I can find a way not to lose frames and not to re-encode.

  Thanks for any help or suggestions.

• Trim video file to edit-out silent parts

  18 décembre 2018, par karel

  I have video recordings of webinars with long silent gaps in them. I need to edit out the silent parts (both the audio and corresponding video tracks). I need to do this through a linux command and be able to do this as a batch action for several video files.
  Ideal scenario is to run a command that :

  1. detects long silent gaps (longer than defined time threshold, e.g. 5
     seconds)
  2. cuts out long silent sections and leaves only 5 seconds of
     silent video bet ween all ’loud’ video sections.

  In another post I found this great script (below). It does the job, but it a) doesn’t leave in extra silent 5 seconds of video which I need after every ’loud’ video part, and b) doesn’t compile produced video files into one composed video file (this problem is less of an issue for me, although it would be great to do that in the same command).

  I didn’t figure out how to modify the script to do this.

  Thanks beforehand for any suggestion.

  ffmpeg -i input.mkv -filter_complex "[0:a]silencedetect=n=-90dB:d=0.3[outa]" -map [outa] -f s16le -y /dev/null |& F=’-aq 70 -v warning’ perl -ne ’INIT $ss=0 ; $se=0 ; if (/silence_start : (\S+)/) $ss=$1 ; $ctr+=1 ; printf "ffmpeg -nostdin -i input.mkv -ss %f -t %f $ENVF -y %03d.mkv\n", $se, ($ss-$se), $ctr ; if (/silence_end : (\S+)/) $se=$1 ; END printf "ffmpeg -nostdin -i input.mkv -ss %f $ENVF -y %03d.mkv\n", $se, $ctr+1 ; ’ | bash -x

• Encoding from FFMPEG to MPEG-DASH, WebM with Keyframe Clusters to work with MediaSource API

  1er mai 2016, par Chris Nolet

  I’m currently sending a video stream to Chrome, to play via the MediaSource API.

  As I understand it, MediaSource only supports MP4 files encoded with MPEG-DASH, or WebM files that have clusters beginning with keyframes (otherwise it raises the error : Media segment did not begin with keyframe).

  Is there any way to encode in MPEG-DASH or keyframed WebM formats with FFMPEG in real-time ?

  EDIT :

  I just tried it with ffmpeg ... -f webm -vcodec vp8 -g 1 ... so that every frame is a keyframe. Not the ideal solution. It does work with MediaStream now though. Any way to sync up the segments with the keyframes in WebM so not every frame needs to be a keyframe ?

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  Reference Questions on WebM / MP4 and MediaSource :

  Media Source Api not working for a custom webm file (Chrome Version 23.0.1271.97 m)

  MediaSource API and mp4