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• FFmpeg CRF control using x264 vs libvpx-vp9

  19 octobre 2016, par igon

  I have some experience using ffmpeg with x264 and I wanted to do a comparison with libvpx-vp9. I tested a simple single pass encoding of a raw video, varying the crf settings and presets both with x264 and libvpx-vp9. I am new to libvpx and I followed this and this carefully but I might have still specified wrong combination of parameters since the results I get do not make much sense to me.

  For x264 I did:

  ffmpeg -i test_video.y4m -c:v libx264 -threads 1 -crf  -preset  -y output.mkv 
  

  and obtained the following results:

  codec  , settings                        , time        , PSNR      ,bitrate
  libx264,['-crf', '20', '-preset', 'fast'],13.1897280216, 42.938337 ,15728
  libx264,['-crf', '20', '-preset', 'medium'],16.80494689, 42.879753 ,15287
  libx264,['-crf', '20', '-preset', 'slow'],25.1142120361, 42.919206 ,15400
  libx264,['-crf', '30', '-preset', 'fast'],8.79047083855, 37.975141 ,4106
  libx264,['-crf', '30', '-preset', 'medium'],9.936599016, 37.713778 ,3749
  libx264,['-crf', '30', '-preset', 'slow'],13.0959510803, 37.569511 ,3555
  

  This makes sense to me, given a crf value you get a value of PSNR and changing the preset can decrease the bitrate but increase the time to encode.

  For libvpx-vp9 I did:

  ffmpeg -i test_video.y4m -c:v libvpx-vp9 -threads 1 -crf  -cpu-used  -y output.mkv 
  

  First of all I thought from tutorials online that the -cpu-used option is equivalent to -preset in x264. Is that correct? If so what is the difference with -quality? Furthermore since the range goes from -8 to 8 I assumed that negative values where the fast options while positive values the slowest. Results I get are very confusing though:

  codec     , settings                      , time        , PSNR     ,bitrate
  libvpx-vp9,['-crf', '20', '-cpu-used', '-2'],19.6644911766,32.54317,571
  libvpx-vp9,['-crf', '20', '-cpu-used', '0'],176.670887947,32.69899,564
  libvpx-vp9,['-crf', '20', '-cpu-used', '2'],20.0206270218,32.54317,571
  libvpx-vp9,['-crf', '30', '-cpu-used', '-2'],19.7931578159,32.54317,571
  libvpx-vp9,['-crf', '30', '-cpu-used', '0'],176.587754965,32.69899,564
  libvpx-vp9,['-crf', '30', '-cpu-used', '2'],19.8394429684,32.54317,571
  

  Bitrate is very low and PSNR seems unaffected by the crf setting (and very low compared to x264). The -cpu-used setting has very minimal impact and also seems that -2 and 2 are the same option.. What am I missing? I expected libvpx to take more time to encode (which is definitely true) but at the same time higher quality transcodes. What parameters should I use to have a fair comparison with x264?

  Edit: Thanks to @mulvya and this doc I figured that to work in crf mode with libvpx I have to add -b:v 0. I re-ran my tests and I get:

      codec     , settings                                 , time        , PSNR     ,bitrate
  libvpx-vp9,['-crf', '20', '-b:v', '0', '-cpu-used', '-2'],57.6835780144,45.111158,17908
  libvpx-vp9,['-crf', '20', '-b:v', '0', '-cpu-used', '0'] ,401.360313892,45.285367,17431
  libvpx-vp9,['-crf', '20', '-b:v', '0', '-cpu-used', '2'] ,57.4941239357,45.111158,17908
  libvpx-vp9,['-crf', '30', '-b:v', '0', '-cpu-used', '-2'],49.175855875,42.588178,11085
  libvpx-vp9,['-crf', '30', '-b:v', '0', '-cpu-used', '0'] ,347.158324957,42.782194,10935
  libvpx-vp9,['-crf', '30', '-b:v', '0', '-cpu-used', '2'] ,49.1892938614,42.588178,11085
  

  PSNR and bitrate went up significantly by adding -b:v 0

• Setting EBP data via FFMPEG

  14 octobre 2016, par user2475310

  With FFMPEG can we insert EBP data on certain frames? If so what is the command?

  We have IDR frames that must have EPB data.

• Does libx265 and libx264 libraries implement a decoder ?

  10 octobre 2016, par Kevino

  I have one question about these 2 codec library developped by videolan.

  Does x265(libx265) implements a decoder? Same question for x264(libx264).

  Thank you for your answers.

• How does one encode a series of images into H264 using the x264 C API ?

  23 septembre 2016, par Rella

  How does one use the x264 C API to encode RBG images into H264 frames? I already created a sequence of RBG images, how can I now transform that sequence into a sequence of H264 frames? In particular, how do I encode this sequence of RGB images into a sequence of H264 frame consisting of a single initial H264 keyframe followed by dependent H264 frames?

• Issue with openh264enc gstreamer plugin and tcp connections

  20 septembre 2016, par agaldos

  I am trying to stream over TCP encoded video into a EC2 Instance. Using "x264enc" encoder, all works correctly. I get the frames and generate the video correctly.

  The issue comes when I try to use the "openh264enc" encoder.

  If I put in the server "nc -l -p 5555" I can check that data is arriving into the port but when I put the pipeline goes to PREROLLING state and nothing more happens. If I cut the process in the sender, this message appears in the server:

  ubuntu@ip-172-31-87-56:~$ gst-launch-1.0 -e -v tcpserversrc host=ec2-52-29-128-23.eu-central-1.compute.amazonaws.com port=5555 ! h264parse ! mpegtsmux ! filesink location=file.ts
  Setting pipeline to PAUSED ...
  /GstPipeline:pipeline0/GstTCPServerSrc:tcpserversrc0: current-port = 5555
  Pipeline is PREROLLING ...
  ERROR: from element /GstPipeline:pipeline0/GstH264Parse:h264parse0: No valid frames found before end of stream
  Additional debug info:
  gstbaseparse.c(1281): gst_base_parse_sink_event_default (): /GstPipeline:pipeline0/GstH264Parse:h264parse0  
  ERROR: pipeline doesn't want to preroll.
  Setting pipeline to NULL ...
  /GstPipeline:pipeline0/GstTCPServerSrc:tcpserversrc0: current-port = 0
  Freeing pipeline ...
  

  Pipeline used in the EC2 Instance, the server:

  gst-launch-1.0 -e -v tcpserversrc host=ec2-52-29-128-23.eu-central-1.compute.amazonaws.com port=5555 ! h264parse ! mpegtsmux ! filesink location=file.ts
  

  Sender pipeline with x264enc:

  gst-launch-1.0 -e videotestsrc horizontal-speed=5 ! x264enc ! tcpclientsink port=5555 host=52.29.128.23
  

  Sender pipeline with openh264enc:

  gst-launch-1.0 -e videotestsrc horizontal-speed=5 ! openh264enc ! tcpclientsink port=5555 host=52.29.128.23