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x264 encoding low res fast, high res slower/later

Looking for advice on settings for fast encoding a lower quality video

2:57 am on May 7, 2010 (gmt 0)

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joined:Apr 25, 2008
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Hello everyone,

I'm setting up a video site in my school district that will be for both public and private use. I have ffmpeg installed with a bunch of libraries, but as of now we are going to be encoding with x264. I have been browsing the web and I've found some good settings for a high quality stream, but it's taking way too long for the encoding (1hr video = 10hr rendering).

I'm wondering if anyone has some good presets for a youtube-style conversion, where I can do a quicker, low res pass and then do my higher res pass over a longer stretch of time.

I will be using the jw player with a plugin to do the switch between the resolutions.

Any advice is much appreciated!
8:14 am on May 9, 2010 (gmt 0)

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10 hours is pretty excessive unless that is HD? Slow CPU? Also keep in mind when encoding using more modern codecs with higher compression it just takes longer.

I can't give you any specific settings but I will mention there's a direct relation between resolution and bitrate. I'll use MPEG2 for DVD as an example because it's what I'm most familiar with but this applies to any compressed video.

Generally when you're using a resolution of 720X480 which is the max for NTSC DVD you're going to want to use a bitrate between 8000kbps and 4000kbps. When you get above 8000 you'll get diminishing returns especially if you have a very good source video, in other words you're just creating a bigger file with no benefit. When you start to go below the 4000kbps mark you'll start to get excessive macroblocking, it goes downhill fast below that especially with poor quality source video. You're better off dropping the resolution at this point. You'll have less detail but the video will not have any artifacts.

Exactly where the sweet spot is depends on a lot of things. WMV and other mpeg4 variants can produce great video at a much lower bitrate than MPEG2, the max you might want to go with WMV for 720X480 might be around 2000kbps.

The content is big factor too. Clean video from a DV camcorder shot on a tripod of some guy sitting at a desk is not going to need the same amount of bitrate as an action packed noisy VHS tape that was hand held.

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