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• ARM compiler shoot-out, round 2

       
  20 août 2009, par Mans — ARM, Compilers

  In my recent test of ARM compilers, I had to leave out Texas Instrument’s compiler since it failed to build FFmpeg. Since then, the TI compiler team has been busy fixing bugs, and a snapshot I was given to test was able to build enough of a somewhat patched FFmpeg that I can now present round two in this shoot-out.

  The contenders this time were the fastest GCC variant from round one, ARM RVCT, and newcomer TI TMS470. With the same rules as last time, the exact versions and optimisation options were like this :

  • CodeSourcery GCC 2009q1 (based on 4.3.3), -mfpu=neon -mfloat-abi=softfp -mcpu=cortex-a8 -std=c99 -fomit-frame-pointer -O3 -fno-math-errno -fno-signed-zeros -fno-tree-vectorize
  • ARM RVCT 4.0 Build 591, -mfpu=neon -mfloat-abi=softfp -mcpu=cortex-a8 -std=c99 -fomit-frame-pointer -O3 -fno-math-errno -fno-signed-zeros
  • TI TMS470 4.7.0-a9229, --float_support=vfpv3 -mv=7a8 -O3 -mf=5

  
  To keep things fair, I left the vectoriser off also with the TI compiler. The table below lists the decoding times for the sample files, this time normalised against the participating GCC compiler. Remember, smaller numbers are better. Also keep in mind that this test was done with a development snapshot of TMS470, not an approved release.

  Sample name	Codec	Code type	GCC	RVCT	TI
  cathedral	H.264 CABAC	integer	1.00	0.95	1.02
  NeroAVC	H.264 CABAC	integer	1.00	0.96	1.05
  indiana_jones_4	H.264 CAVLC	integer	1.00	0.92	1.02
  NeroRecodeSample	MPEG-4 ASP	integer	1.00	1.01	1.08
  Silent_Light	MP3	64-bit integer	1.00	0.48	0.72
  When_I_Grow_Up	FLAC	integer	1.00	0.87	0.93
  Lumme-Badloop	Vorbis	float	1.00	0.94	1.05
  Canyon	AC-3	float	1.00	0.88	1.01
  lotr	DTS	float	1.00	1.00	1.08

  Overall, the TI TMS470 compiler comes off slightly worse than GCC. In two cases, however, it was significantly better than GCC, but not as good as RVCT. Incidentally, those were also the ones where RVCT scored the biggest win over GCC.

  My conclusions from this test are twofold :

  • ARM’s own compiler is very hard to beat. They do seem to know how their chips work.
  • GCC is incredibly bad at 64-bit arithmetic on 32-bit machines.

  The logical next step is to test these compilers with vectorisation enabled. FFmpeg should offer plenty of opportunities for this feature to shine. Unfortunately, that test will have to wait until the RVCT vectoriser is fixed. The current release does not compile FFmpeg with vectorisation enabled.

• Why is ffmpeg transcoding speed going down over time ?

  24 mars 2021, par Nikola R.

  I'm executing basic ffmpeg command to transcode input MP4 video to output MP4 video (both using H264 as video codec, and stripping out audio, for simplicity) :

  



  ffmpeg -i input-video.mp4 -b:v 20000k -an -vcodec libx264 output-video.mp4


  



  Transcoding is initially pretty fast (around 60-70 fps for first 20 or so frames), and then starts dropping steadily, ending at around 30 fps after 5000 frames.

  



  Is this inherent behavior ? If so, why does it happen ?
Also, is there any better option for the command line that would improve speed (besides using -threads) ?

  



  Would it be better to cut the input video and process it as smaller chunks, getting overall higher speed per sequence ? (I'm afraid that chunking might affect encoder's RD optimization)

  


• Using ffmpeg to generate dash manifest and it cannot be played by dash.js

  18 mars 2019, par Punkhead

  I’m using ffmpeg to encode incoming stream via rtmp protocol, the code as following :

  ffmpeg -re -i rtmp://localhost:1935${StreamPath} -use_timeline 1 /
  
  -use_template 1 -window_size 10 -min_seg_duration 5000 -f dash out.mpd

  The manifest looks like this :

  <?xml version="1.0" encoding="utf-8"?>
  
  <mpd xmlns="urn:mpeg:dash:schema:mpd:2011" profiles="urn:mpeg:dash:profile:isoff-live:2011" type="static" mediapresentationduration="PT1M36.4S" minbuffertime="PT8.3S">
  
      <programinformation>
  
      </programinformation>
  
      <period start="PT0.0S">
  
          <adaptationset contenttype="video" segmentalignment="true" bitstreamswitching="true" framerate="30/1">
  
          <representation mimetype="video/mp4" codecs="avc1.640028" width="1920" height="1080" framerate="30/1">
  
              <segmenttemplate timescale="15360" initialization="init-stream$RepresentationID$.m4s" media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startnumber="4">
  
                  <segmenttimeline>
  
                      <s t="384000" d="128000"></s>
  
                      <s d="71680"></s>
  
                      <s d="128000" r="4"></s>
  
                      <s d="56832"></s>
  
                      <s d="128000"></s>
  
                      <s d="72704"></s>
  
                  </segmenttimeline>
  
              </segmenttemplate>
  
          </representation>
  
      </adaptationset>
  
      <adaptationset contenttype="audio" segmentalignment="true" bitstreamswitching="true">
  
          <representation mimetype="audio/mp4" codecs="mp4a.40.2" bandwidth="128000" audiosamplingrate="44100">
  
              <audiochannelconfiguration schemeiduri="urn:mpeg:dash:23003:3:audio_channel_configuration:2011" value="2"></audiochannelconfiguration>
  
              <segmenttemplate timescale="44100" initialization="init-stream$RepresentationID$.m4s" media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startnumber="4">
  
                  <segmenttimeline>
  
                      <s t="1099755" d="367616"></s>
  
                      <s d="205824"></s>
  
                      <s d="367616" r="4"></s>
  
                      <s d="162816"></s>
  
                      <s d="367616"></s>
  
                      <s d="207872"></s>
  
                  </segmenttimeline>
  
              </segmenttemplate>
  
          </representation>
  
      </adaptationset>
  
  </period>
  
  </mpd>

  When I try to play it on dash.js player, a error occured :

  [112] Parsing complete: ( xml2json: 3.50ms, objectiron: 1.76ms, total: 0.00526s) Debug.js:127 
  
  [116] SegmentTimeline detected using calculated Live Edge Time Debug.js:127 
  
  [118] MediaSource attached to element.  Waiting on open... Debug.js:127 
  
  [119] Manifest has been refreshed at Tue Jan 02 2018 01:57:35 GMT+0800 [1514829455.1] Debug.js:127 
  
  [155] MediaSource is open! Debug.js:127 
  
  [156] Duration successfully set to: 96.4 Debug.js:127 
  
  [157] Added 0 inline events Debug.js:127 
  
  [158] video codec: video/mp4;codecs="avc1.640028" Stream.js:225 
  
  Uncaught TypeError: Cannot read property 'type' of null
  
      at z (Stream.js:225)
  
      at C (Stream.js:285)
  
      at D (Stream.js:373)
  
      at E (Stream.js:398)
  
      at Object.d [as activate] (Stream.js:107)
  
      at y (StreamController.js:363)
  
      at MediaSource.c (StreamController.js:342)

  then it fails to playback...

  Is it because I didn’t set the parameters right on ffmpeg or this is a bug in dash.js ?

  I really stuck here !