h.264 confusion

[kcgixflix]

Hi all,

New to the forum, but have been reading for a very long time. I'm striving to nomilize my video in the same way that I've done with my audio over the years. Audio was easy; MP3s are commonplace... granted, not the most efficient or highest quality, but seemingly universally accepted. With video, it's a different story. I'm kind of under the impression that h.264/AVC mp4 will do for video what mp3 did for audio. If I'm wrong, I really need to know because I've spent an outrageous amount of time transcoding to AVC with many failures. I have tons of videos in multiple formats that I'd like to organize. I try to envision future trends and formats to save myself time, but it's hard to keep up. My goal for video is the same as I'd imagine most people's: high quality playback and small file size that can played on multiple sources (desktop, notebook and portable media players). Notebook is a 2GHz Celeron POS and my pmp is 5.5 gen 80g Ipod. Yeah I know it's proprietary, but I love the user interface and I've not found a reliable open source pmp.

My question: Is h.264/AVC conversion worth all the time I'm putting into it??? I'm willing to keep transcoding and even upgrade hardware, but it's gotta be for a good reason.

I realize I've left out many specifics. If it makes any difference, my background is high end user, no programming, mostly Windows, some Mac and tiny amount of Linux. Thanks for any general feedback.

[celtic_druid]

I'd say that MPEG-4 Part 2 (XviD, DivX, etc.) would be more like the video equiv of mp3. AVC is more like the aac audio that goes along with it.

If the video has to be iPod compatible then that limits you. 640x480 baseline profile @ level? with a bitrate limit of 768? Something along those lines. If you search I am sure you can find the specs or use something that includes an iPod profile.

[edDV]

h.264 crys out for hardware acceleration for playback and full hardware encoding. When that happens, real time PVR/DVR type systems will become practical and MPeg4 will replace MPeg2 for many applications including computer based home recording.

Until then, slow software based h.264 encoders will have limited appeal.

[kcgixflix]

Video does not have to be Ipod compatible even though specs have been upped to "Low Complexity" 1500kbps. I'm am very willing to archive in another more common format and transcode to Ipod on an as needed basis. I tried Divx and found it appealing, but discovered it wasn't ultimately what I was searching for. I've not tried Xvid... thanks celtic_druid for the suggestion. I will seriously look into that format.

[kcgixflix]

edDV: Truly! The hardware limitations are cumbersome. My desktop does a pretty good job encoding and decoding, but the notebook is obviously too wimpy even with the most efficient software decoders. I guess I'm spending too much time trying to potentially guess and future-proof my immediate work. I did the same thing years ago with mp3's. Thanks for your feedback. I really like MPeg2 and will default to that if Xvid doesn't strike me. The weirdest part about all this is that when I do encode (as an experiment) in h.264/AVC (from mpeg2), I use the exact specs from the source and end up with a larger file size as outupt! I realize that you can drop bitrates for both audio and video to maintain the same aud/vid output quality, but I at least thought that identical bitrates would yeild smaller file sizes with more efficient codecs. There's much for me to learn.

[jagabo]

I tried Divx and found it appealing, but discovered it wasn't ultimately what I was searching for.

What was the problem with Divx? Xvid is an MPEG 4 part 2 codec just like Divx. You will run into the same issues.

[edDV]

In theory, MPeg4 AVC can achieve similar results to MPeg2 at half the bitrate but that assumes both start from an uncompressed source. Converting MPeg2 to MPeg4 will perform less well.

[Cornucopia]

The weirdest part about all this is that when I do encode (as an experiment) in h.264/AVC (from mpeg2), I use the exact specs from the source and end up with a larger file size as outupt! I realize that you can drop bitrates for both audio and video to maintain the same aud/vid output quality, but I at least thought that identical bitrates would yeild smaller file sizes with more efficient codecs. There's much for me to learn.

1st thing to learn:

Filesize = Bitrate (assume CBR, or VBR average) * Length (time)

If you have a source that is fast motion 24bit720x480@29.97fps lasting 5 minutes, and you make MPEG1, MPEG2, MPEG4-ASP (Divx, Xvid, etc), and h.264 versions--ALL averaging 2Mbps, this is what you'll end up with:

MPEG1--size=~75MB, quality=very bad during motion, fuzzy (maybe bad) otherwise
MPEG2--size=~75MB, quality=bad during motion, semi-decent otherwise
MPEG4--size=~75MB, quality=fair during motion, pretty good otherwise
h.264--size=~75MB, quality=very good during motion, great otherwise

Notice, the size is about the same.

2nd thing to learn:

Don't keep re-encoding! Get a uncompressed/losslessly compressed source, and compress it ONCE to your destination format. Recompression=BAD!

Scott

[kcgixflix]

No wonder I've been having so much trouble. I've been going about this entriely the wrong way by recompressing everything. Thanks to everyone for excellent explanations!

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