AVI to H264 equivalent bitrates

[supernano]

I was using a media player that read xvid encoded videos, so I used avidemux to encode all my videos to avi. In general, I encoded using two-pass with an average bitrate of 1500kbps.
I have now gotten an iPhone, and I'd like to use avidemux to convert all avi my videos to mp4 encoded with H264. I've read that H264 has a better compression algorithm and I can get the same quality at lower bitrates, so if I encode using two-pass, what average bitrate should I use to mantain similar quality in my videos?

[guns1inger]

There is no magic number. The appropriate bitrate will vary from video to video. Better to do a quality based encode instead and let the file size fall where it may.

[supernano]

Ok, thanks. Is there anyway then to determine the quality of my avi files? I just don't want to set the quality unnecessarily high.
In avidemux I can set for quality either constant rate factor or constant quantiser, and the value between 0(high quality) and 51(low quality). Is there a value that's standard for DVD quality?

[guns1inger]

I would use Xvid4PSP or Handbrake, rather than AVI Demux, because they use X264, which is a better encoder.

I would then do a CQ (Constant Quantiser) encoding starting with a value of 21. If the quality isn't good enough, move up to 20, then 18

[rumplestiltskin]

Handbrake is great. When I transcode AVI to H264 I simply use the same filesize and set the audio bitrates to match. I end up with about the same video bitrate and the quality is fine. One possible bug in Handbrake: Be sure to set the proper framerate; don't rely upon "same as source" as I've seen a number of conversions produce jerky results; when I manually set the framerate to match the source, I don't have any problems.

[redwudz]

Try roughly a 1/3 less bitrate. Maybe 800Kb/s for H.264 compared to 1500Kb/s for Xvid and see how it looks.

[Pongydog]

So If I have a h264 video file at about 850kbps to keep similar quality in Xvid I'd be looking at encoding the Xvid at a third higher bitrate (about 1133kbps). Is that correct?

[Cornucopia]

If you buy MediaPlayerPro ($1.99USD) app, it will NATIVELY play Divx/Xvid AVIs, MKVs, etc on your iPhone (iOS v4.3 or later) - no conversion needed!

Scott

[Selur]

So If I have a h264 video file at about 850kbps to keep similar quality in Xvid I'd be looking at encoding the Xvid at a third higher bitrate (about 1133kbps). Is that correct?

No, what he said was, that if you reencode the (exact) same source with Xvid and x264 you need roughly 1/3 bit rate for the x264 than for the Xvid encode for them to have the same quality.
If you reencode the Xvid encode you will lose quality, since the encoding with Xvid (probably) introduced (a lot) new artifacts, which for the encoder will be new details and thus the 'same source' criteria is gone.
(The other way around reencoding a H.264 file, you also do not have the same source, so simply using 1/3 more bitrate will not produce the same quality.)

[enim]

If you buy MediaPlayerPro ($1.99USD) app, it will NATIVELY play Divx/Xvid AVIs, MKVs, etc on your iPhone (iOS v4.3 or later) - no conversion needed!

I would rather go for MediaPlayerPro ($1.99USD) , if I have more than one videos, plus rather than going into process of re-encoding hassles.