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Buffering speed, stalls, solutions?
Flash buffering
rocknbil




msg:3636811
 4:12 pm on Apr 28, 2008 (gmt 0)

This is not really a Flash question. I have video exported externally into a Flash object. Works great, most of the time. Smooth streaming, very few stalls. 320 X 240 resolution across the board, optimized .flv.

I have an Internet connection shared between multiple computers (satellite, ugh) so between computer A and B, we have an identical connection fed to the comps via ethernet connected to a router.

Computer A, 1.2 Ghz, 2 GB RAM, streams these videos perfectly.

Computer B, 700 mhz, 2 GB RAM, the streaming can't keep up with the play. My Flash object has a streaming indicator and a current mark indicator, the current mark is always right against the end of the stream, stalls frequently.

One would think this is strictly a problem with the CPU (Which, i personally don't understand, what's this got to do with download time?)

Enter computer C, at a different location, 2 GB RAM, 3.5 Ghz, connected via DSL (256K I believe.) Same hiccup/stall problem. This, by the way, is a newer comp, only a year old.

At this point I'm guessing the two are two different issues, on the DSL connection it's a problem with the DSL, on computer B, it's the processor speed.

There are about 20 videos, all loaded externally on demand via a playlist and of different lengths, and I've spread a variety of optimization values across them finding a balance between resolution and quality. Regardless of the video, these two comps always hiccup and stall.

Any other ideas with what could interfere with the download speed? Possible issues to look at and correct?

Research with random samples (visitors, etc.) report no problems, guessing everyone else has better comps and connections.

 

thecoalman




msg:3637234
 1:52 am on Apr 29, 2008 (gmt 0)

The CPU becomes a factor because of compression, compressed video is made of what is called a GOP (group of pictures) I don't know what it is for .flv but for dvd compliant MPEG it's 15 frames. The first frame is an I-frame which is full frame of data, subsequent frames will be made up of data from the I-frame and previous frames. For .flv the GOP will much longer, the longer the GOP the more CPU required because these frames are generated each time the video is played.

It may simply be stalling because you don't have enough CPU to render the video. Have you tried playing it locally?

As for computer C I'm assuming you meant 256kbps?

What bitrate are you encoding at? that's going to be pretty close to what a video of that size would need for an acceptable quality.

rocknbil




msg:3638130
 1:07 am on Apr 30, 2008 (gmt 0)

Ahhhh . . .yeah . . stepping into gray area here for me . . . . when the original .mpg is created, I think it's set to 5000 kbps video, then the Adobe CS3 encoder for the .flv is set for 400 kbps using On2 VP6, audio MPEG III @ 96 kbps. I fiddled around with it until I got the best balance between file size and quality, that seems to be where it's at at the moment.

Many of the older ones would have been encoded at various settings, but all would have been re-encoded at the same settings for the .flv. Don't even know if that answers the question. :-P

thecoalman




msg:3638265
 8:00 am on Apr 30, 2008 (gmt 0)

when the original .mpg is created, I think it's set to 5000 kbps video,

For the best results you should be encoding from whatever the source is if possible. If for example your original video is from a DV-AVI cam you should edit it and output as DV-AVI, then bring it into your encoder. Using MPEG as a middleman will degrade the final output. Restoration aside the less you do to video the better final product you'll have. Numerous reencodes will result in a poorer final product. If you're using a really good clean source you can use a lower bitrate.

Say for example we have a original video that is DV-AVI and you encode it too 500kbps WMV. If we also encode the original DV-AVI video to a 5000kbps MPEG to achieve the same results as the 500kbps video from this MPEG you may have to use 600kbps because the MPEG is a lower quality source.

That's just an example and those numbers are not to be taken at face value, the point is the better source you have the better result you'll get at lower bitrates. A DV-AVI FYI does not have a GOP, each frmae is individually encoded hence the larger file size of 14GB's an hour.

---------------------------

As far as th stuttering goes on computer C if the connection is 256kbps and you're encoding at 400kbps(note that probably includes both audio and video) then it would have to buffer about 1/3 the video before it will play smoothly from end to end. The only real solution is a faster connection or lower bitrate if you want people on connections like that to be able view it quickly without stuttering.

How it's buffered is dictated by the player, I don't know exactly how it works for flash. I don't see anything under settings when I right click a youtube video so it must have a default setting. Players like Windows Media Player allow the user to set it to whatever they want, by default it calculates the size of the file and your connection speed to determine how much to buffer before it begins playing so it can play smooth until the end but I've seen similar problems such as you describe on really high bitrate video that is higher than my connection speed..

I can't really give you any advice specifically for flash because I don't use it. There may be a solution I'm not aware of for slower connections such as if you could override how the buffering is handled.

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