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• ffmpeg is setting start_time to a negative value on output

  16 mai 2016, par Éric

  We’ve been using an old version of ffmpeg for a while and now we need to upgrade to a more recent version (e.g. 2.6) and we have issues with it while converting .mov to .mp4.

  For instance I have a .mov video file that has two streams, video and audio, both with start_time=0 and when I convert it using :

  ffmpeg -i my_file.mov my_file.mp4

  the output mp4 has an audio stream with start_time=-0.021333.

  The FORMAT section, as shown by ffprobe -show_format -show_streams my_file.mp4
  also has start_time=-0.021333

  The previous version of ffmpeg we were using didn’t have this issue...

  When we play the output mp4 file in a web browser using < video > it’s all good while playing but if we pause the video and seek here and there we notice that all the frames are off by 1. The first frame is duplicated and the last frame is missing !

  In other words :

  dom.currentTime = 0 shows the first frame
  
  dom.currentTime = 1/24 (fps is 24) shows the first frame again
  
  dom.currentTime = 2/24 shows the second frame instead of the third frame
  
  dom.currentTime = 3/24 shows the third frame instead of the fourth frame
  
  ...

  We believe this is caused by the field start_time=-0.021333

  This is a major issue for us...

  It’s repro on chrome and firefox but somehow safari is not having issues with this...

  After googling this we found that we’re not the only one with this issue but it’s not clear what the solution is.

  Someone suggested to use the "-c:a copy" arguments and it worked on some files but gave an error on some others :

  Could not write header for output file #0 (incorrect codec parameters ?) : Invalid argument

  So this doesn’t seem to be a robust solution...

  Any help would be appreciated.

• aaccoder : rewrite PNS implementation

  6 septembre 2015, par Rostislav Pehlivanov

  aaccoder : rewrite PNS implementation
  This commit rewrites the PNS implementation and significantly
  
  improves sonic quality.
  The previous implementation marked an incredibly big amount
  
  of SFBs to predict when there was no need for this and this
  
  resulted in quite a large amount of artifacts. Also the
  
  quantization was incorrect (av_clip(4+log2f(...))) which
  
  led to 3x the intensity for PNS values leading to even more
  
  artifacts.
  This commit rewrites the PNS search function and introduces
  
  a major change : the PNS values are synthesized and are compared
  
  to the current coefficients in addition to passing through
  
  the revised checks to see whether PNS can be used.
  This decreases distortions and makes the current PNS implementation
  
  mainly focused on replacing any low-power non-zero bands as well
  
  as adding any zeroed bands back.
  The current encoder’s performance is enough (especially with
  
  IS) so PNS isn’t really required except to fill in the occasional
  
  few bands as well as extend any zeroed high frequency, so this
  
  combination which is already enabled by default works
  
  to get as much quality as it can within the bits allowed.
  Signed-off-by : Rostislav Pehlivanov <atomnuker@gmail.com>
  

  • [DH] libavcodec/aaccoder.c

• Solution for VB6 to broadcast Webcam

  11 juillet 2014, par vantrung -cuncon

  Sorry, I know VB6 is decades ago, but I’m in a situation that I have to use VB6 to deliver live webcam stream beetween 2 PC in Server - Client Model program. Vb6-code holds the connection then I have no choice but to transfer all data via that connection.

  I’ve tried weeks for this, uncountable approaches but went to nowhere.
  My efforts focused on 3 major approaches :

  1/ Use ffmpeg to record live webcam as ".avi" file on hard disk, transfer parts of file to other end & play it. But I’ve stucked with a media-player that can play a "being written" avi file.

  Windows Media Player control told me "file already in use..." & VLC Plugin can’t even be added to VB6 (axvlc.dll).

  2/ Use ffmpeg to save live webcam as avi file, transfer each bit of that file to the other end, then in other end, extract 24 images / second from the avi to display continously in a picture box.
  This approach is ok except that my hard disk get fulled of images in a time of wink and my program get very slow before hanging.

  3/ Use ffmpeg to stream the live webcam to a rtp-port like this :

  ffmpeg -f dshow -i video="Lenovo EasyCamera" -vcodec mpeg2video -pix_fmt yuv422p -f rtp -an rtp://224.1.2.3:8191

  I’ve successfully watch the stream in VLC, but VLC(axvlc.dll) refused to be integrated into ancient VB6. And more important, I don’t know how to redirect/reroute the rtp stream to other PC with VB6.

  Any one please light me up ? (Any 3rd party component is welcomed)