[pineapple]

I'm planning to buy an Acer n311 but I found a problem with the video playback when I tried it in the shop.

I brought 2 video clips with me on a SD card. Both are 640 X 480 @30fps, the video bitrate is 512kbps. The first one is a WMV file and the other one is Mpeg.

I tried to play both video with the Media Player but the image is very jerky. Then the shop assistant installed the TCPMP player and tried again but still, can't get a good result.

Could anyone tell me how can I make a playable video clip with optimal picture quality? what file tye and what bitrate should I use?

[pineapple]

I'm planning to buy an Acer n311 but I found a problem with the video playback when I tried it in the shop.

I brought 2 video clips with me on a SD card. Both are 640 X 480 @30fps, the video bitrate is 512kbps. The first one is a WMV file and the other one is Mpeg.

I tried to play both video with the Media Player but the image is very jerky. Then the shop assistant installed the TCPMP player and tried again but still, can't get a good result.

Could anyone tell me how can I make a playable video clip with optimal picture quality? what file tye and what bitrate should I use?

[Andy Whiteford]

The biggest issue with the n311 is full screen update as the 400mhz cpu seems to struggle with updating a full VGA resolution screen. To improve movie playback, i would recommend resizing your movie to 320x240 or perhaps a little bigger and also a lower bit rate - say between 150 and 250kbps for a 320x240 res movie. You can use TCPMP player to stretch this move during playback to fill the screen.

[karlth]

I bought a N310 yesterday (300mhz) and I am simply awestruck with the lack of video performance.

It is obvious that the processor has no problem handling the load of streaming a VGA video onscreen. The problem is that either the video memory or controller seems to be stunningly slow.

I bought the PDA for use as a in-car video player for my daughter (converted DVDs) so it is proving to be a major disappointment.

[Andy Whiteford]

Originally Posted by karlth

It is obvious that the processor has no problem handling the load of streaming a VGA video onscreen. The problem is that either the video memory or controller seems to be stunningly slow.

What makes you say this? You do realise that the cpu does most of the work on the Acer and memory is shared like most other Pocket PCs. I personally don't think the 400mhz cpu is up to the job of full screen VGA (unless static or slow moving) and I imagine the 300mhz would only be worse in this respect. Multimedia is not the n300 series strong point although otherwise, it is a great Pocket PC.

[karlth]

The effect you see is a page flip effect. Which is why I think it is the video memory or controller.

I converted the "The Invincibles" trailer to 320x240 (175kbs), and ran it from Memory, with PocketDVD and during the fast switching scenes you could actually see how the new frame was being drawn across screen.

My other PocketPC is a I-Mate JAM which runs the 175Mhz IMAP CPU and it handles it with no problems, even reading from a SD card.

The funny thing is that the initial reviews of the N311 mentioned this problem but then actual users stated that video performance really wasn't an issue. :?

I am using TCPMP and converting the DVDs to <200Kbs bitrates so I must be missing something.

[Andy Whiteford]

Originally Posted by karlth

The effect you see is a page flip effect. Which is why I think it is the video memory or controller.

I converted the "The Invincibles" trailer to 320x240 (175kbs), and ran it from Memory, with PocketDVD and during the fast switching scenes you could actually see how the new frame was being drawn across screen.

You have to remember though that the cpu is having to process the video data and update the screen. Using a lower resolution or bit rate of movie will help as it means there is less video data to process however even if the movie is 320x240, this is still being played back on a 640x480 screen and although only 320x240 worth of video data is being processed, the full 640x480 screen resolution still needs to be updated. The difference between manipulating 76800 pixels (320x240) and 307200 pixels (640x480) is quite substantial, especially when these pixels need to be changed very quickly such as fast action scenes in a movie.

[karlth]

That is true but if the processor is overloaded you get frameskips or stuttering - as the CPU is decoding the file. That does not seem to be a problem with the N310 though. There is not stuttering.

When the PDA is playing a movie it goes through the following steps:

1. Read stream to memory buffer.
2. Decode frame.
3. Display frame.
4. Loop to step 1 or 2 based on memory buffer status.

1 or 2 is limited by the CPU, memory and disk IO speed. There seems to be no problem here as there is no stuttering.

Step 3 is on the other hand limited by video memory(shared) and the video controller.

[Andy Whiteford]

I know I get stuttering or poor frame rates when I try to use too high a resolution/bit rate which is why I stick to movies that I have encoded for QVGA. There may be other elements at play here as well or it could even be a physical limitation of the actual screen - I don't know the full process of how the Acer is getting the final image displayed and what potential pitfalls there may be.

[karlth]

I'll do some encoding tests later today and report if I find an acceptable setting.

[kool-ed]

The N300 display is handled by a Nvidia GoForce 4000, a 3 year old graphical chip and unfortunately not fast enough to handle VGA videos with high frame. Movies can be watched at 30fps in CIF resolution (352 x 288), according to Nvidia. That would explain why the framerate drops when trying to manipulate 4 times more pixels...

As everyone have seen, QVGA videos are more... acceptable