MPEG 2 bitrate - anything lower than 10Mbps?

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Level 1

131 points

MPEG 2 bitrate - anything lower than 10Mbps?

I use MPEG 2 program stream files for our Cable station's playback system (a Leightronix Nexus). Compressor creates good MPEG 2 files, but they're far larger than we prefer. The minimum bitrate I can set is 10Mbps.

Our video sources are mostly 2-4Mbps, many are 320x240, so there's nothing to gain by bumping this up to 10Mbps for playback. The files also become too large and will fill our storage system faster than necessary.

In the old (pre-App Store) Compressor I was able to edit the preset file in a text editor to generate something at a lower quality. The new Compressor's presets are easier to edit, but Compressor itself is too smart. If it sees a bitrate lower than the minimum, it uses the default of 18Mbps.

Is anyone aware of a way to use a bitrate lower than 10Mbps for MPEG 2 program streams in Compressor? I really like Compressor's workflow so I'm hoping we don't need to look for something else.

Thanks!

Posted on Oct 27, 2015 8:09 AM

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Answer 1

BenB

Level 6

13,184 points

Oct 27, 2015 12:56 PM in response to Mitch Cohen

320x240 for television playback? That destroys a lot of quality, doesn't it?

Standard Definition for broadcast is 720x480, and applied to an MPEG-2 transport stream, I can lower the average bit rate to 2, and the max to 2.35. HD minimum is 10.

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Answer 2

Mitch Cohen Author

Level 1

131 points

Oct 28, 2015 9:59 AM in response to BenB

Bingo! I hadn't thought to force a specific frame size. Forcing 720x480 (or 720x576), as you state, brings the slider down as low as 2Mbps. Voila - thank you.

This is Public Access Government TV in a small town. Meetings average 1hr, but vary widely and unpredictably. Our two main meeting rooms record on DVD-R decks in four-hour mode, which is (on every deck I've ever seen) 320x240, at roughly 2Mbps, to get four hours of video (with MPEG-2 audio) to fit on the 4.7GB DVD-R. The video from these meetings are converted from the VOB on the DVD to MPEG-2 using MPEG StreamClip then moved to our playback system. Playback quality is pretty good; these are generally very static video shots; not a lot of motion where the size and compression would be prominent.

Other meetings are recorded on newer (digital) equipment, and the above DVD decks will eventually be replaced. These have higher bitrates as they aren't constrained by DVD sizes, but overall file length still needs to be managed due to program length. These are the videos we need to convert to MPEG-2. In informal tests, we don't see much of a quality improvement using much higher bitrates at playback. I'm guessing we'll settle on 4Mbps.

We think about file sizes due to the volume and storage needs. Last year we recorded 276 hours of meetings, which we attempt to maintain permanently in MPEG-2 format (as well as DVD's and H.264 for web).

We also broadcast non-Government public access TV programs, which have a completely different set of criteria. These are more typical programs with more motion thus a higher bitrate demand, so we do that. But we don't worry about long-term storage, so as we need space we're ok trashing old programs others have submitted.

All our broadcasts are in NTSC standard definition. I don't see the cable company giving us a real HD channel for many years.

I hope that's not too much info. Thanks again for the help.

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