[Server-devel] problem with media player module on XS- moodle

[James Cameron]

On Tue, Jun 07, 2011 at 05:06:59PM +1000, James Cameron wrote:
> 5.  describe the frame rate and resolution of the video content, since
> these determine the CPU and video bandwidth requirements,

10fps, 480x360, H.264 with AAC, 525 kbps.

> 6.  provide a sample video file for download that demonstrates the
> problem,

The sample did not demonstrate the problem.  See below.

> 7.  test what CPU utilisation is observed, using top over SSH,

50% CPU utilisation observed here.

--

Thank you for the sample video.

Please understand that .flv, and the other file types you described
(.ogg, .avi, .mp4, .mpeg) are container formats, and cannot be used to
predict the playback resources required for a video.

The video and audio inside the container file is what matters ... the
resolution, frame rate, and codec of the video determines performance
reliability.

The XO-1 is a capable platform, but it has limits.

Recommend that you vary the process used to prepare the video until
you reach a performance quality that is satisfactory.  In particular,
vary the resolution, frame rate, and codec.  There is no need to vary
the container format, and no real benefit to performance quality in
doing so.

--

Your video file with md5sum d17e5fb6dfdf33ada4fa0889d5ef4d61 and size
2540185 bytes was a Macromedia Flash Video container with an H.264
video stream, resolution 480x360, 10 frames per second, 525 kilobits
per second, with an AAC audio stream, mono, 44100 Hz sample rate.

To compare, I looked in YouTube for a similar video, and found key
2s13X66BFd8, which after downloading with clive was a Macromedia Flash
Video container with a Flash video stream, resolution 320x240, 10
frames per second, 262 kilobits per second, with an MP3 audio stream,
stereo, 22050 Hz sample rate.

Testing the CPU usage on my desktop system, the CPU was used for 5% of
the time for your video, and 1% of the time for the YouTube video.
This was a 5:1 CPU usage difference, and is consistent with the
different resolution and bit rate.

Testing on XO-1 with 10.1.3 build os860, and 11.2.0 build os22, here
are the results:

1.  the .flv file type was not recognised by Browse, either locally or
via HTTP, and so could not be played, only downloaded to Journal,
where it also could not be played,

2.  the video streams in the file could not be processed by Totem,
despite extra codecs being installed,

3.  after installing the VLC video player, both videos played fine
without pauses or audio breaks, your video consuming 45-50% of CPU
time, and the YouTube video consuming 7-10% of CPU time, again a ratio
of five to one,

Conclusion: your resolution and codec choice has magnified the CPU
cost by a factor of five as compared to the resolution and codec used
by YouTube.

The test did not reproduce the symptom you described, probably because
the videos were not being played inside a web browser.

Please provide a sample video for _download_ within Browse or Firefox.
Mail attachment apparently doesn't trigger the symptom.

Or provide a suitable HTML wrapper.  Thanks!

-- 
James Cameron
http://quozl.linux.org.au/