1st Question! Why can't compact cam give small video size?

[lastboltnut]

As stated above, why all the compact cam with Video mode so inefficient in file size for video?

Thanks.

[yowch]

Poor compression, processor slow, read-write to media slow.

For mainstream video, MiniDV is still pretty much the way to go.

[filofari]

i believe most, if not all compact cams uses motion JPEG instead of MPEG compression. Thats why it has a poor compression ratio.

[lastboltnut]

Slow processor may be....media shouldn't be a problem as I can use SD card to watch very highbandwidth video on my PDA/Laptop...what do you think?

Originally Posted by yowch Poor compression, processor slow, read-write to media slow. For mainstream video, MiniDV is still pretty much the way to go.

Huh? I tot MPEG is a collection of JPEG liao? Not har....

Or may be they are trying to force us to buy another delicated V-Cam, so that they can make more $?

Originally Posted by filofari i believe most, if not all compact cams uses motion JPEG instead of MPEG compression. Thats why it has a poor compression ratio.

Originally Posted by filofari i believe most, if not all compact cams uses motion JPEG instead of MPEG compression. Thats why it has a poor compression ratio.

[filofari]

nope.. MPEG and MJPEG is 2 different things. MJPEG is actually JPEGs stacked together to form a video (so the only compression done is when its converted to JPEG) and as for MPEG its does its coding differently.

If you are interested you can read http://www.fileformat.info/format/mpeg/egff.htm for more information. It explains the concepts of MPEG and MJPEG clearly.

[Del_CtrlnoAlt]

Originally Posted by lastboltnut Slow processor may be....media shouldn't be a problem as I can use SD card to watch very highbandwidth video on my PDA/Laptop...what do you think?

when u watch highbandwidth = READ from SD, but when you are recording its WRITE... so must see if your SD card can support fast write anot, its between 1/2 to 75% of the actual read speed normally.

[AReality]

So anyone converts their MJPEG vids from digicams to DivX format?
Or only me do that...


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[Del_CtrlnoAlt]

Originally Posted by AReality So anyone converts their MJPEG vids from digicams to DivX format? Or only me do that... .

hmm... mjpeg got sound anot? btw, how big your raw file to make u wanna do DIVX compression...

[yowch]

Generally this happens:
1. The sensor/mic reads the light/sound and translates to electrical signals.
2. The processor first reads the raw signal and record internally as images/sound/data.
3. The compression processor then compresses the raw data into whatever format (MiniDV, DVD, MPEG, DivX, etc.)
4. Then the compressed data is written onto the media (tape, card, harddisc or optical disc).

When you read, the data is retrieved from the media, decompressed by the processor into RAW signal, and sent to the output (monitor, speakers). That is the reverse of the image/sound capture.

The problem is the compressor and the writer. If you have very fast compressor and very fast writer, then you can do a DivX on the go at hi-res and write ontot he fastest media. But not everyone wants compression, especially those who needs lots of post-editing. MiniDV and it brothers are acceptable compression by most indie video, but TV broadcast will reject most miniDV unless no-choice. So, to write less compressed data means faster write needed. To write faster with more compression means that the compression compressor must really fast.

On chips, fast means power-hungry and over-heating.

That's why there is always compromises.

[lastboltnut]

Ok guys, thanks for the info.

Originally Posted by filofari nope.. MPEG and MJPEG is 2 different things. MJPEG is actually JPEGs stacked together to form a video (so the only compression done is when its converted to JPEG) and as for MPEG its does its coding differently. If you are interested you can read http://www.fileformat.info/format/mpeg/egff.htm for more information. It explains the concepts of MPEG and MJPEG clearly.

Originally Posted by Del_CtrlnoAlt when u watch highbandwidth = READ from SD, but when you are recording its WRITE... so must see if your SD card can support fast write anot, its between 1/2 to 75% of the actual read speed normally.

[lastboltnut]

I convert them to Xvid. The size goes down by about 70-75%!

Originally Posted by AReality So anyone converts their MJPEG vids from digicams to DivX format? Or only me do that... .

[lastboltnut]

My Canon S3 IS can take video (VGA) with stereo sound for about 8min with 1Gb SD card! So inefficient...so I need to convert to Xvid loh...

Originally Posted by Del_CtrlnoAlt hmm... mjpeg got sound anot? btw, how big your raw file to make u wanna do DIVX compression...

[dreamerz]

big file size is mainly due to compression...the other factor tat make up bigger file size is data collected eg.exposure,color,lighting,resolution...

[AReality]

Originally Posted by Del_CtrlnoAlt hmm... mjpeg got sound anot? btw, how big your raw file to make u wanna do DIVX compression...

on the Fuji F30,

1GB is about 14 mins, at 640x480.

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