Resizing avi files

[curious d]

Hi. I take a number of videos of my children on my digital camera. These files tend to be really big. Not only is the original size of these video files too big, but they don't play well on the phone (using TCPMP free). I read somewhere that it may be that the bitrate is too high for the phone media player. In the past, I have placed the video files on a DVD using Adobe Premiere and then ripped the DVD and then condensed the video to an Xvid file to save space on my expansion memory card. This all seems so cumbersome to me. I'm looking for a very simple way (preferably freeware) to maintain as much quality as possible while reducing the size of each file so that it will play well on a Windows Mobile phone (avi to smaller avi conversion essentially) without chewing up too much memory on the expansion card. In a couple of months, I expect to have a new phone that may accommodate 640x480 resolution. Thanks.

Sorry if this is the wrong section. I couldn't figure which would be the best place for this request.

[von_Runkel]

If it is just a AVI->AVI conversion, use Virtualdub. Open the AVI, resize it to 640x480 (640x360 if it's widescreen footage), choose "Video Compression - Xvid" and save it as AVI.

My 3 year old Windows Mobile Phone, Qtek 9000, can handle Xvid encodings up to circa 1500 Kbps without stuttering.

Depending on your footage, you can lower the bitrate and frame size to save space. Try 512x288 (widescreen) or 512x384 (4:3) with a bitrate of 500-1000 Kbps. You need to find a balance between frame size and bitrate.

You can also encode to Windows Media (.wmv) with the free Windows Media Encoder from Microsoft and play the videos with the built-in Windows Media Player. However, I found that the Xvid videos played with TCMP was a better choice: smaller file sizes, better visual quality, easier and faster to encode.

[curious d]

Thanks for the info. I'm able to reduce the size of the files in half by encoding into XVID. The bitrate was around 887 kps, but I found that if I reduced the size of a one hour thirty minute file to 250MB, the bitrate will drop to around 261 kps. It doesn't look too bad on my computer and so I'll check it out on my phone. Thanks again.

[curious d]

I think I'm lacking in understanding certain fundamentals. I had a video file encoded in DIVX with a bit rate of over 1100 according to GSpot. The size of the original file is 384MB. I sent VirtualDub to use XVID instead (am I compressing and already compressed video file?) at a bitrate much lower (see previous post for setting). Audio was set to direct streaming and filter was set to reduce the video size to 320x240. I expected the resultant file to be smaller due to the reduced bitrate and screen size, but the resultant file is nearly the same size. What is the reason for this?

I suspect that the videos that I have from my digital camera are not the usual compression and that is why things can be reduced in size. I'm wondering that since my other file is already compressed, there isn't much more to compress and the file remains the same size. That's only a guess on my end. Can someone enlighten me on what I perceive is a misconception (or simply got it totally wrong) on my part? Thanks.

[Gavino]

I expected the resultant file to be smaller due to the reduced bitrate and screen size, but the resultant file is nearly the same size. What is the reason for this?
Since "file size = bitrate x duration", your new file clearly doesn't have a reduced bitrate.
Perhaps you inadvertently set video to "direct stream copy" as well as the audio?

[curious d]

The setting was to full processing mode. Since file size is a product of bitrate and duration, how would reducing screen size factor into the equation? I tried to reduce the screen size of another video with just direct streaming for audio and video and it seemed to reduce the size of the file by 64%. It didn't work for the example I set in the previous post. I also noticed that when I had altered the bitrate on my home video, I accidentally encoded in PAL format. When I re-encoded to NTSC, the file was larger (almost twice as large). I wasn't certain if that made a difference as well. Again, I feel like I'm lacking a certain understanding and I'm doing something wrong without realizing it. Thanks again for the help.

[Guest]

Since file size is a product of bitrate and duration, how would reducing screen size factor into the equation? Simply by allowing you to choose a smaller bitrate without destroying quality.

[CWR03]

Since file size is a product of bitrate and duration, how would reducing screen size factor into the equation?
It might explain better if you look at it the other way: if you were to reduce the bitrate by half and keep the same frame size, you'll notice a significant to severe introduction of artifacts, or an introduction of large pixels. Reducing the bitrate and the frame size together will lose detail (especially noticeable when viewing the file full-screen on a large PC monitor) but you won't notice it on a phone with such a small display.

[Ghitulescu]

The best would be to select the screen size of your cellphone (so many pixels wide x so many pixels height) as the encoding parameter. In case the cellphone does not display the videos in full screen, you have to resize it accordingly.
Then you can encode some 20-30 seconds at various bitrates to see how it will look like, if you like it keep it.

[curious d]

Thanks for all the replies. It seems that other than reducing bitrate and perhaps screen resolution, there isn't another way to save space. Is there a way to determine the minimum bitrate that would yield a decent viewing experience on a cellphone (at 640 x 480 or 320 x 240 resolution)? I'm guessing it is dependent on the movie type (ie. lots of action sceens) and it is variable (thus, it is trial and error).

Also, does compression to NTSC vs PAL make a difference in size? Does converting from PAL to NTSC affect quality?

[Ghitulescu]

Yes, here is a way to find that bitrate: you do yourself experiments with various bitrates and pick up the most suitable one.

[von_Runkel]

Also, does compression to NTSC vs PAL make a difference in size?

If you can choose between PAL and NTSC when shooting your videos, use NTSC for scenes with high motion and PAL for the rest. NTSC has higher frame rate and PAL bigger frame size, so in general the encoded files will have similar sizes. If the camera is very basic, i.e a camera for still pictures with some video capability added, then it may only be the frame rate that differs. And this NTSC/PAL setting is sometimes only used for viewing video on a TV directly from the camera's TV out jack.
Does converting from PAL to NTSC affect quality?
Converting between PAL and NTSC always affects quality in a negative way. However, you should never have to do any conversion because your smartphone can handle both the 29.97 (NTSC) and the 25 (PAL) frame rates.

[2Bdecided]

I've never seen one of these things that lets you choose PAL/NTSC. IME It's always NTSC frame rate, or a fraction thereof - e.g. 60fps, 30fps, 15fps, while the frame sizes are always computer-ish frame sizes (square pixel).

The PAL/NTSC switch in the menu is for the external video output (if it has one).

Cheers,
David.

[iffybob]

question -

how well do rescaling algorythems work now, scaling up is one thing but scaling down is anothe, by 2 or 4 etc is one thing but to scale down by 3.2 is another, is it still better to scale down below the resolution, and place black boarders, to reduce artifacts.

I havent done any, but I did do some on still images (way back), I did get some resolution combos that produced artifacts, ( contrast lines ), and some just looked "cartoony".

[von_Runkel]

how well do rescaling algorythems work now
You need to experiment with this and see if the output is looking OK or not.
On one device that I own (a iPod Video 5.5g), the 16:9 view mode (the device is 4:3 but can letterbox 16:9 content) is using nearest neighbour, which of course is fast but useless. For this device, I always scale to the correct size before encoding.