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• What is faster, Raw PCM audio files, or mp3 files decoded with FFmpeg ?

  8 janvier 2020, par Matthew Strom

  I’m pretty deep into the development of my Android app, and as I mess around with my audio files a second time to try longer audio clips (1000ms long), I am now getting audio glitches again. Before I was not getting any glitches with 160ms long files.

  • Background : I’m making a metronome, so imagine roughly 100 lines of code in the callback to constantly figure out what audio file to play and for how long.

  Without getting into my code, I was just wondering if file size or file type has any impact on performance ? I believe I’m using the sample Player rendering class (source) (for Raw file input) which seems to load the audio data of the file each callback. This would Perhaps loading data from a larger array would slow it down ? Although, It could also be the new features/logic that I’m adding to the callback.

  I know it is talked about frequently about using mp3’s and decoding with FFmpeg. Has anyone done any bench-marking between mp3 and raw, and is there any performance advantage to using mp3’s, or is it mainly to cut down on your APK size ?

  Sorry if this has been discussed somewhere, however, I wasn’t able to find any articles mentioning this aspect between the two file types. Looking more closely at the rendering class, my gut tells me that file size "shouldn’t" be a factor... Otherwise I’ll continue to debug and maybe get some systraces in if I can.

• Is there a way to apply a curve bend in ffmpeg ?

  25 mars 2020, par stevendesu

  I have four cameras each feeding me a different portion of a basketball court. Due to the slight offset of the cameras physical locations and lens distortion around the edges of the camera, I cannot simply stitch the videos together without some kind of correction.

  I’ve looked into ffmpeg’s perspective filter, as well as the lenscorrection filter. In the former case it was only able to create a trapezoid, not the curved image I want. In the latter case using negative values to k1 and k2 seemed to be heading in the right direction, but it either disorted the top and bottom of the image to the point of being nonsensical noise, or it zoomed in to the image so much that I lost important details.

  For the sample picture below, ultimately I want the midcourt line (the blue vertical line on the right side) to be vertical, and I want the mess of wires on the white desk at the bottom to remain visible and identifiable.

  Given a video which looks like the following :

  

  I wish to produce something like the following :

  

  This image was made using the "Curve Bend" filter in GIMP, but I just eye-balled it - so it’s not perfect. Ideally once I get the exact parameters the midcourt line will be perfectly vertical

  When using the lenscorrection filter, no values for k1 and k2 seemed to get the effect I want :

  Negative k1, negative k2 :

  

  Negative k1, positive k2 :

  

  Positive k1, negative k2 :

  

  Positive k1, positive k2 :

  

  In general :

  • negative / negative distorted the image beyond recognition
  • negative / positive looked alright, but the midcourt line was off the screen and it wasn’t clear if any distortion had been applied
  • positive / negative looked the best, but while the top and bottom curved in the middle of the left and right actually bulged out, leaving the midcourt line distorted
  • positive / positive was the opposite of the desired effect

• Using Unicast RTSP URIs via ffmpeg

  6 août 2019, par Chris Marshall

  I’m fairly new to ffmpeg, so I’d certainly appreciate being given an "M" to "RTFM." The ffmpeg docs are...not-so-easy...to navigate, but I’m trying.

  The goal is to develop a compiled server that incorporates ffmpeg, but first, I need to get it working via CLI.

  I have a standard AXIS Surveillance camera (AXIS M5525-E), set up as an ONVIF device (but that isn’t really relevant to this issue).

  When I query it, I get the following URI as its video streaming URI :

  rtsp://192.168.4.12/onvif-media/media.amp?profile=profile_1_jpeg&streamtype=unicast

  The IP is local to a sandboxed network.

  I add the authentication parameters to it, like so :

  rtsp://<login>:<password>@192.168.4.12/onvif-media/media.amp?profile=profile_1_jpeg&amp;streamtype=unicast
  
  </password></login>

  (Yeah, I know that’s not secure, but this is just for testing and feasibility study. The whole damn sandbox is an insecure mess).

  Now, if I use VLC to open the URI, it works great (of course). Looking at it with a packet analyzer, I see the following negotiation between the device and my computer (at .2 - Clipped for brevity) :

  Id = 11
  
  Source = 192.168.4.12
  
  Destination = 192.168.4.2
  
  Captured Length = 82
  
  Packet Length = 82
  
  Protocol = TCP
  
  Date Received = 2019-08-06 12:18:37 +0000
  
  Time Delta = 1.342024087905884
  
  Information = 554 -> 53755 ([ECN, ACK, SYN], Seq=696764098, Ack=3139240483, Win=28960)
  
                      °
  
                      °
  
                      °
  
  Id = 48
  
  Source = 192.168.4.12
  
  Destination = 192.168.4.2
  
  Captured Length = 366
  
  Packet Length = 366
  
  Protocol = TCP
  
  Date Received = 2019-08-06 12:18:38 +0000
  
  Time Delta = 2.09382700920105
  
  Information = 554 -> 53755 ([ACK, PUSH], Seq=696765606, Ack=3139242268, Win=1073)

  Followed immediately by UDP stream packets.

  If, however, I feed the same URI to ffmpeg :

  ffmpeg -i rtsp://<login>:<password>@192.168.4.12/onvif-media/media.amp?profile=profile_1_jpeg&amp;streamtype=unicast -c:v libx264 -crf 21 -preset veryfast -g 30 -sc_threshold 0 -f hls -hls_time 4 /Volumes/Development/webroot/fftest/stream.m3u8
  
  </password></login>

  I get nothing. No negotiation at all between the device and my computer.

  After that, if I then remove the &streamtype=unicast argument, I get a negotiation, and a stream :

  Id = 10
  
  Source = 192.168.4.12
  
  Destination = 192.168.4.2
  
  Captured Length = 82
  
  Packet Length = 82
  
  Protocol = TCP
  
  Date Received = 2019-08-06 10:37:48 +0000
  
  Time Delta = 3.047425985336304
  
  Information = 554 -> 49606 ([ECN, ACK, SYN], Seq=457514925, Ack=2138974173, Win=28960)
  
                      °
  
                      °
  
                      °
  
  Id = 31
  
  Source = 192.168.4.12
  
  Destination = 192.168.4.2
  
  Captured Length = 345
  
  Packet Length = 345
  
  Protocol = TCP
  
  Date Received = 2019-08-06 10:37:49 +0000
  
  Time Delta = 3.840152025222778
  
  Information = 554 -> 49606 ([ACK, PUSH], Seq=457516393, Ack=2138975704, Win=1039)

  I will, of course, be continuing to work out why this is [not] happening, and will post any solutions that I find, but, like I said, I’m fairly new to this, so it’s entirely possible that I’m missing some basic stuff, and would appreciate any guidance.

  Thanks !