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Linsys A/V Synchronization Tests

Here are my results from A/V sync testing on the Linsys SDI cards.

Versions

  • Linsys master driver 2.7.1
  • MLT git head as of March 12, 2011
  • FFmpeg v0.6.1 Ubuntu package
  • libdv 1.0.0 Ubuntu package
  • dvthumbs.c

Methodology

  1. Prepare a raw DV file from uncompressed sources from Tektronix MTS4EA tool. This is NTSC SD format.
  2. Use dvthumbs program compiled against libdv to generate reference thumbnails for both audio and video. The files are named with frame numbers to make it easy to compare the corresponding audio for video. The thumbnails below show perfect sync. The white block in the top left corner indicates when the tone starts playing. Here are frames 269 and 270; the video is on top and the audio on bottom:
    dvthumbs-000269.png dvthumbs-000270.png
    waveforms-000269.png waveforms-000270.png
  3. I can only test SD using this methodology (due to the Canopus converter) and NTSC SD is more problematic with Linsys cards requiring special producer on HD Master and not supported at all with MLT module on SD Vidport. Therefore, I converted the NTSC to PAL using melt:
    melt -profile dv_pal clapperboard.dv -consumer avformat:clapperboard-pal.dv
  4. Use dvthumbs program compiled against libdv to generate reference thumbnails for the PAL source test clip.
    Studying a few samples show the audio starts somewhere around 15 ms after the start of the frame. This is to be expected since the frame duration changed from 33 to 40 ms. Here are frames 224 and 225:
    dvthumbs-000224.png dvthumbs-000225.png
    waveforms-000224.png waveforms-000225.png
  5. Play clapperboard-pal.dv with melt using the sdi consumer and all defaults to play through the Vidport.
  6. Connect the SDI out to a Canopus ADVC-1000.
  7. Connect the Firewire of the Canopus ADVC-1000 to the computer.
  8. Capture a raw DV with Kino.
  9. Run dvthumbs against the raw capture file.

Results

I ran the test 3 times for each board. Below are thumbnails from the same region of the test clip. As you can see from the reference thumbnails, the audio tone begins when the white block appears in the top left corner of the video. When the audio waveform does not start at the beginning of the thumbnail, we can easily guess that it is about 1/4 or 1/2 of the way through one frame and therefore its offset in tens of milliseconds.

Vidport

Test 1 - 219 & 220 Test 2 - 286 & 287 Test 3 - 235 & 236
dvthumbs-000219.png dvthumbs-000220.png
waveforms-000219.png waveforms-000220.png 		dvthumbs-000286.png dvthumbs-000287.png
waveforms-000286.png waveforms-000287.png 		dvthumbs-000235.png dvthumbs-000236.png
waveforms-000235.png waveforms-000236.png

HD Master

Test 1 - 558 & 559 Test 2 - 204 & 205 Test 3 - 366 & 367
dvthumbs-000558.png dvthumbs-000559.png
waveforms-000558.png waveforms-000559.png 		dvthumbs-000204.png dvthumbs-000205.png
waveforms-000204.png waveforms-000205.png 		dvthumbs-000366.png dvthumbs-000367.png
waveforms-000366.png waveforms-000367.png

Summary

On the SD Vidport, A/V sync can be considered perfect. On the HD Master, the audio is consistently ahead by roughly 30 ms. That is not so bad! And one can compensate by attaching the filter sox:'delay 0.03' to the consumer.

-- DanDennedy - 2011-03-12

Attachments Attachments
Topic attachments
I Attachment Action Size Date Who Comment
PNGpng dvthumbs-000204.png manage 3.5 K 2011-03-13 - 05:25 DanDennedy  
PNGpng dvthumbs-000205.png manage 3.5 K 2011-03-13 - 05:25 DanDennedy  
PNGpng dvthumbs-000219.png manage 3.5 K 2011-03-13 - 04:52 DanDennedy  
PNGpng dvthumbs-000220.png manage 3.6 K 2011-03-13 - 04:53 DanDennedy  
PNGpng dvthumbs-000224.png manage 3.4 K 2011-03-13 - 04:46 DanDennedy  
PNGpng dvthumbs-000225.png manage 3.5 K 2011-03-13 - 04:46 DanDennedy  
PNGpng dvthumbs-000235.png manage 3.5 K 2011-03-13 - 05:12 DanDennedy  
PNGpng dvthumbs-000236.png manage 3.6 K 2011-03-13 - 05:12 DanDennedy  
PNGpng dvthumbs-000269.png manage 3.0 K 2011-03-13 - 04:37 DanDennedy  
PNGpng dvthumbs-000270.png manage 3.0 K 2011-03-13 - 04:38 DanDennedy  
PNGpng dvthumbs-000286.png manage 3.5 K 2011-03-13 - 05:04 DanDennedy  
PNGpng dvthumbs-000287.png manage 3.6 K 2011-03-13 - 05:05 DanDennedy  
PNGpng dvthumbs-000366.png manage 3.5 K 2011-03-13 - 05:29 DanDennedy  
PNGpng dvthumbs-000367.png manage 3.5 K 2011-03-13 - 05:30 DanDennedy  
PNGpng dvthumbs-000558.png manage 3.5 K 2011-03-13 - 05:20 DanDennedy  
PNGpng dvthumbs-000559.png manage 3.6 K 2011-03-13 - 05:20 DanDennedy  
C source code filec dvthumbs.c manage 4.0 K 2011-03-13 - 05:31 DanDennedy source code of dvthumbs utility that uses libdv
PNGpng waveforms-000204.png manage 0.3 K 2011-03-13 - 05:26 DanDennedy  
PNGpng waveforms-000205.png manage 0.3 K 2011-03-13 - 05:26 DanDennedy  
PNGpng waveforms-000219.png manage 0.2 K 2011-03-13 - 04:53 DanDennedy  
PNGpng waveforms-000220.png manage 0.3 K 2011-03-13 - 04:54 DanDennedy  
PNGpng waveforms-000224.png manage 0.2 K 2011-03-13 - 04:48 DanDennedy  
PNGpng waveforms-000225.png manage 0.2 K 2011-03-13 - 04:48 DanDennedy  
PNGpng waveforms-000235.png manage 0.2 K 2011-03-13 - 05:13 DanDennedy  
PNGpng waveforms-000236.png manage 0.3 K 2011-03-13 - 05:13 DanDennedy  
PNGpng waveforms-000269.png manage 0.2 K 2011-03-13 - 04:39 DanDennedy  
PNGpng waveforms-000270.png manage 0.3 K 2011-03-13 - 04:40 DanDennedy  
PNGpng waveforms-000286.png manage 0.2 K 2011-03-13 - 05:05 DanDennedy  
PNGpng waveforms-000287.png manage 0.3 K 2011-03-13 - 05:06 DanDennedy  
PNGpng waveforms-000366.png manage 0.3 K 2011-03-13 - 05:30 DanDennedy  
PNGpng waveforms-000367.png manage 0.3 K 2011-03-13 - 05:30 DanDennedy  
PNGpng waveforms-000558.png manage 0.3 K 2011-03-13 - 05:21 DanDennedy  
PNGpng waveforms-000559.png manage 0.3 K 2011-03-13 - 05:21 DanDennedy  
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Topic revision: r2 - 2011-03-13 - DanDennedy
 
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