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doubts about codecs and compressions

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Michel Domaine
doubts about codecs and compressions
on Nov 11, 2010 at 2:28:44 pm

Hi everybody,

First of all I am sorry for my english.

I lost a night for this, so I thought to ask to the Cow!

I had to edit a video assembling a lot of different videos, most of all mp4 or mov in h264 codec (not a great quality).
I worked and I've exported to animation to have an intermediate codec.
Then, after some client's correction, I had to compress in the best possible quality for a wall projection from a pc.

I used compressor and I made three videos (1024x576, 10 minutes long) to test:

-mpeg4 at the best
-quicktime h264 at the best
-mpeg2 at vbr average bitrate 18, pick bitrate 30

What I saw is that:
- mpeg4 and h264 degraded a lot the contrast and show a lot of broken pixel, it was really bad.
- mpeg2 (with compressor saying 720 pal 16:9) wasn't 1024x576, but 720x404, it had less details on the graphics, but contrast and colors were good, near to the animation.

So my questions are:

- why compressor makes mpeg2 pal 16:9 so little and not in a standard 1024x576?
- we know that in a lot of case best codec for internet is mp4 or mov h264, but for a presentation or a projection (as in my example) which is the best format and codec?

thanks everyone and sorry if my description was so long!!! ;)


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Chris Blair
Re: doubts about codecs and compressions
on Nov 12, 2010 at 2:02:43 am

Michel Domaine wrote:
-mpeg4 at the best
-quicktime h264 at the best
-mpeg2 at vbr average bitrate 18, pick bitrate 30



You'd have to provide a lot more details about your settings before anyone could help. That's not really enough information. H.264 can look as good as MPEG2 at nearly half the data rate, so you shouldn't see as big a difference in quality. MPEG2 can be compressed to both SD and HD sizes, and you're using square pixel, widescreen SD Pal at 1024x576. My guess is you have the pixel aspect set wrong in your settings and it's resizing based on that....but that's just a guess.

Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com
Read our blog http://www.videomi.com/blog


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Michel Domaine
Re: doubts about codecs and compressions
on Nov 12, 2010 at 11:23:20 am

Thanks for the answer Chris!

First of all, I used compressor 3.5.3

Here I put the settings from the info window:

MPEG4

Name: MPEG-4
Description: MPEG-4 video with AAC audio at 48kHz. Settings based off the source resolution and frame-rate.
File Extension: mp4
Estimated size: 99.99 MB
Audio Encoder
Format: MPEG4
Sample Rate: 48.000kHz
Channels: 2
Bits Per Sample: 16
AAC encoder quality: high
Data rate: 256 Kbps
Video Encoder
Format: MPEG4
Width: (100% of source)
Height: (100% of source)
Selected: 1024 x 576
Pixel aspect ratio: Square
Crop: None
Padding: None
Frame rate: 25
Frame Controls: Automatically selected: Off
ISMA Profile: 0
Variable bit rate, high quality
Enhanced Podcast: Off

MOV H264

Name: QuickTime H.264
Description: H.264 video with stereo AAC audio. Settings based off the source resolution and frame-rate.
File Extension: mov
Estimated size: unknown
Audio Encoder
AAC, Stereo (L R), 48,000 kHz
Video Encoder
Format: QT
Width: (100% of source)
Height: (100% of source)
Selected: 1024 x 576
Pixel aspect ratio: Square
Crop: None
Padding: None
Frame rate: (100% of source)
Selected: 25
Frame Controls: Automatically selected: Off
Codec Type: H.264
Multi-pass: On, frame reorder: On
Pixel depth: 24
Spatial quality: 100
Min. Spatial quality: 25
Temporal quality: 50
Min. temporal quality: 25



MPEG2

Name: Program Stream
Description: MPEG-2 Program Stream with MPEG audio at 48kHz. Settings based off the source resolution and frame-rate.
File Extension: mpeg
Estimated size: 1.3 GB
Type: MPEG-2 program stream
Video Encoder
Format: M2V
Width and Height: Automatic
Selected: 720 x 576
Pixel aspect ratio: PAL CCIR 601 (16:9)
Crop: None
Padding: None
Frame rate: (100% of source)
Selected: 25
Frame Controls: Automatically selected: Off
Start timecode from source
Aspect ratio: Automatic
Selected 16:9
Field dominance: Automatic:
Selected Progressive
Average bit rate: 17 (Mbps)
2 Pass VBR enabled
Maximum bit rate: 30 (Mbps)
High quality
Best motion estimation
Closed GOP Size: 12, Structure: IBBP
Audio Encoder
Format: MPEG
Sample Rate: 48.000kHz
Channels: 2
Bits Per Sample: 16

The problem is that with compressor I can't change pixel aspect ratio on mpeg2, so it's impossible to put it square.
And it's really strange, cause in the finder and with Quicktime dimensions are 720x404. If I use vlc it recognize the video like pal 16:9 and show it at 1024x576.


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Chris Blair
Re: doubts about codecs and compressions
on Nov 12, 2010 at 11:43:15 pm

Quicktime reports some weird things in it's inspector. But your MPEG2 settings show 720x576 at 16:9, which would basically be changing your pixel size from square (1024x576) to rectangular. So you're fine there.

The same thing happens in NTSC world with Quicktime H.264. I can output a 720x486 rectangular pixel 16:9 video and using Quicktime I HAVE to output an 864x486 file to get it to display properly in Quicktime.

The rest of your settings look ok to me, so maybe somebody else can chime in.

Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com
Read our blog http://www.videomi.com/blog


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Michel Domaine
Re: doubts about codecs and compressions
on Nov 13, 2010 at 12:17:43 pm

Maybe it's also cause it's an mpeg and Quicktime doesn't love so much mpeg...

But now, which is the best codec for a presentation or a projection (that could be the same for a good archiving...) ?

And another question... how can I make a mp4 with h264 codec in compressor? I didn't found this setting possible.

Thank you Chris and thanks to everyone.


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