Bitrate is lower than expected after conversion

[pdun459]

Hi. I've recently been converting some MP4s to AVI with XMedia Recode and have a question about the results I'm getting. I'm using Constant Bitrate at 1400 but after encoding, the Media Info says the Bitrate is lower, 1344 in the example screenshot. Shouldn't it be at least 1400? Would anyone be able to tell why the Bitrate is lower? Let me know if more info will help. Thanks.

Edit: Forgot I had another question. XMedia Recode Media Info doesn't show it, but my media player info shows an overall bitrate that's a lot higher than 1400, over 1500 in some cases. Shouldn't Constant Bitrate be just that, 1400 at all times?

[manono]

First, using CBR is a very bad idea. Use either 2-pass VBR (Variable BitRate) encoding or use 1-pass CQ (Constant Quality) encoding. For XviD, 3 is a good quantizer to use.

I don't know for sure, but it's possible the encoder couldn't use the full 1400 during certain parts of the film (dark and/or static or very low motion sections). In any event, I wouldn't worry about that and suggest you learn to encode properly.

The question might also arise of why reencode it at all, and degrade the 'original' quality? It won't improve just because you gave it a higher bitrate, but only get worse.

[DB83]

Well something is clearly incorrect.

Given the adage that filesize = runlength*bitrate your conversion is significantly bigger at a reported lower bitrate. Which is not possible.

But we are not seeing the whole picture. Nether versions show audio bitrate and that must be taken in to account. Also Xvid is not an efficient codec.

[DB83]

- drunk -

[pdun459]

I'm reencoding because my computer is old and it doesn't play these particular MP4s very smoothly. I think it's because they use a High 3.1 Profile. The only profile my computer handles very well is Simple @ L3. I'd love to upgrade but it's just not possible right now.

manono, I tried those VBRs you suggested and there's no question the quality's great but the file sizes are huge, over three times the original. If there's a way to use VBR and get smaller sizes I'd be all for it. I've tried encoding with AVC/H.264 and it takes forever, on my system anyway.

[manono]

manono, I tried those VBRs you suggested and there's no question the quality's great but the file sizes are huge, over three times the original.

If you give it the same bitrate as when doing the CBR encodes, with everything else being equal (same bitrate audio), the one done using VBR will be the same size (give or take) as the one done using CBR. The bitrates are the same, therefore the filesizes will be the same.

[smitbret]

You have much bigger issues than the missing 56kbps.

Your basic line of thinking is OK. It's not necessarily the profile that is your problem, though, it is the codec used in the video stream. Playing back the MPEG-4 L10 (AVC/h264) encoded original is much more taxing on a system than playing back the MPEG-4 L2 file from your destination. That's the same reason it takes forever to re encode. And because every action has an equal and opposite reaction, you need a lot more bitrate for the same quality with the DivX encode. That's probably why you ended up with a file 3x larger. There is really no way to get the same quality at a similar bitrate unless it's just a blank screen.

Size
Speed/Ease of Playback
Quality

Pick 2.

Your best answer here is to save up $20 and get a video card the decodes h264/AVC so you won't have the playback problem in the first place.

http://www.newegg.com/Product/Product.aspx?Item=N82E16814131338

[hello_hello]

I don't use Xmedia Encode, but is it possible when you specify a bitrate it's the bitrate for video and audio? That's what happens when a program has an option to choose a file size. It should include video and audio. The program would calculate the required bitrate and the audio bitrate would be subtracted from that, and what's left is the video bitrate.

To check the bitrate accurately, try Bitrate Viewer.

[pdun459]

smitbret, that's good information. I've always had problems playing AVC/h264 now I know why. I probably could swing a new video card, that's not a bad idea, I'll have to look into it.