Jerky playback/lost frames (not bandwidth problem)

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Jul. 01, 2009nodybod

Hi,
I am new to the world of JW and I'm having some problems.

My videos have jerky playback after uploading. They play fine locally.
It does not seem to be a bandwidth/buffering issue as the video can be fully downloaded.
I have tried various bitrates and formats. FLV,MP4 and different hosting. Local website server and Amazon S3

I use Squeeze 5

The site uses Joomla with the Allvideos plugin.

http://www.webspacevideo.com.au/fishing-trip

Any help would be appreciated

Thanks
Nodybod

Jul. 02, 2009lost

Too much active content on the page.

On a fast CPU (4GHz) I'm seeing about 40% CPU usage when just your imageshow is running.

When Flash is playing plus downloading, the CPU usage goes to about 80%. Once Flash has finished downloading, the CPU usage drops to about 65%.

On a slower CPU, the active content can easily max out the CPU, causing the stuttering.

Open Task Manager, then load your page, then start one of your videos.

Jul. 02, 2009nodybod

Thanks for your reply lost,

I am running a AMD quadcore 2.3ghz with 4gig ram and my CPU usage is maxing at 18% while downloading and playing yet I still see the stuttering.

Could to much active content still be the problem?
I would not think so but I am open to all suggestions.

Thanks Nodybod

Jul. 02, 2009lost

A single video on your page along with the image show plays smoothly for me, because I never got close to 100% CPU, max was about 80%.

Are you sure the 18% is correct?

Jul. 02, 2009nodybod

Yeah just tried again and only 20% and 27%peak CPU while downloading and playing 3 at once.

The video only jerks during the pan shots.
Are you saying the video did not studder for you?


Nodybod

Jul. 02, 2009lost

Jerkiness during panning comes from the encoding process.

Let's say you encode at 20 frames per second with a group of pictures of 40 (keyframe every 2 seconds).

Then the decoder takes the keyframe (a full frame) and constructs the next 40 frames from change data.

If there isn't much change, the docoder isn't working very hard.

If there is panning, the decoder might have to reconstruct 25~50% of the next frame, so it's working very hard. The decoder might not be able to reconstruct the frame in 1/20 of a second, so there is a slight delay until the frame is ready, which causes the jerkiness.

So what can you do about it? Well, depending on the available settings in your encoding software, you can do two-pass encoding with motion estimation. Essentially, the encoder takes a look at the full video to be encoded on the first pass. This gives it a "look ahead" at what might be happening in the next frames so it can encode for large pans. Then on the second pass, the encoder uses the data gathered on the first pass to make a better encode, allowing for panning and other "stuff." Your encoder might have a setting such as "live action", meaning lots of motion and scene changes.

Jul. 02, 2009nodybod

I will try your suggestion in the morning as it's quite late here.
I do have a general understanding of encoding and the video was encoded using a 2 pass.
But I would think (I could be wrong) that if it was due to encoding then it would display the jerkiness on my local pc before I upload it. I use VLC Player to view on my local pc and the video plays fine.

Here are my settings.........jpeg file.
http://www.mediafire.com/imageview.php?quickkey=yzmd0anyvkz&thumb=4

Thanks for all your help Lost
Nodybod

Jul. 02, 2009morktron

Hi Nodybod, looks like maybe you are getting somewhere now thanks to Lost?

I've uploaded a page with just the video to ensure that it was not the page that was causing the video to be jerky.

http://www.webspacevideo.com.au/video-test/

You'll see it is still jerky so it can't be the content of the page.

I've have sneaking suspicion that at the time of writing Flash video is not capable of playing everything smoothly no matter what you do. Hopefully I'm wrong though...

Jul. 02, 2009lost

Flash uses a lot of CPU cycles when it's downloading. I've seen the CPU usage double.

Many users have reported that the playing proceeds smoothly once the downloading is finished, which confirms the heavy CPU usage during downloading.

Additionally, Nodybod has some fairly fast panning in his videos, which increases the decoding load as Flash has to create a large portion of the frame instead of just small changes frame-to-frame. This can be ameliorated somewhat during encoding.

Jul. 06, 2009nodybod

No luck so far.
re your last post Lost.
The video still studders on the panning shots even after the video has fully downloaded and as I said in a previous post it plays fine using VLC player on my local pc.

Any more suggestions?

Jul. 07, 2009lost

VLC and any Flash-based player are completely different, so you cannot compare the two.

I would try using ffmpeg to perform 2-pass transcoding into H.264/MP4 with the best live action settings that I could find using Google, such as: http://lists.mplayerhq.hu/pipermail/mplayer-users/2008-November/075191.html

Jul. 08, 2009nodybod

Can you recommend a good Flash based player?

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