Understanding bitrate

[Jayell]

I'm encoding a 3-minute movie into H.264 format. As one of my friends 'hits the wall'' (the video starts freezing up) with anything higher than about a 1Mb/sec bitrate (or that's been the case with my flv videos)
.. so
Is using a 'constant bitrate' encoding the same as using a variable bitrate with the 'target' and 'maximum' bitrate at the same number. Or is there more involved in the two different types of encoding?

using Premiere Pro CS5

[sidd finch]

VBR allows a higher bitrate (and therefore more storage space) to be allocated to the more complex segments of media files while less space is allocated to less complex segments. The average of these rates can be calculated to produce an average bitrate for the file.

The advantages of VBR are that it produces a better quality-to-space ratio compared to a CBR file of the same data. The bits available are used more flexibly to encode the sound or video data more accurately, with fewer bits used in less demanding passages and more bits used in difficult-to-encode passages.

The disadvantages are that it may take more time to encode, as the process is more complex, and that some hardware might not be compatible with VBR files.VBR may also pose problems when streaming over a dial-up or broadband Internet connection, because the instantaneous bitrate, if unconstrained, may rise above the maximum data transfer speed of the web connection. These problems can be avoided by specifying a maximum instantaneous bitrate during the encoding process.

Sidd

[Jayell]

Thanks for the feedback, Sidd. I'd read similar info .. which is what led me to the question. I guess if I have a low bitrate max (~1000 in my case), using VBR doesn't buy me much.

[Chuck Engels]

VBR will allow the file to be created at a lower bitrate for non motion sections of the video and a higher bit rate during motion. Motion can really look bad when a low bitrate is used so you would either have to use a high constant rate or a variable rate.

The variable rate will allow you to create a higher quality video at a smaller file size, if there is a lot of motion in the video. Variable Bit Rate also allows for 1 or 2 pass (the big guys at the studios have options of using more than 8 passes), 2 passes allows for the bitrate to be more accurately set for each frame of the video and will give you a higher quality but not necessarily a smaller file size.

Whether we us constant bitrate or variable will depend a lot on the contents of the video itself and where/how the final output is to be used or shown. There is no right or wrong answer as there are good times to use either. I find that in most cases using the 2 pass VBR works very well but that is not always the best option.

That's my 2 cents anyway

[Jayell]

Thanks, Chuck .. that did help me understand it a little better.

[George Tyndall]

I find that in most cases using the 2 pass VBR works very well but that is not always the best option.

That's my 2 cents anyway

I always use VBR, 2 pass for encoding with PRE7, and I also change the Quality from the default of 4 to 5, using the slider.

I play the resulting MPEG2 1920x1080i 30 files back from their location on a USB2.0 external HDD (which runs at 5800rpm rather than 7200), and they always look perfect on my 52-inch Samsung.

[Jayell]

Another question related to understanding bitrate.

Sometimes when watching a YouTube video, it will stop and start as the file is loading, playing whatever. On the other hand, a week or so ago I watched a 98-minute video with NO stops-and-starts. What is affecting the smoothness of play more: bitrate, something on the server .. or something else? I'm using the same computer at all times .. and I get about 16Mb/sec download speed.

[Ron]

This is usually server load at the time.

[Jayell]

Ah-hah. Thanks, Ron.

[Matthew Max]

This is a great conversation. My son's smart phone can
handle a very high bitrate, while this laptop of mine, which
is fairly new, handles a much smaller bitrate, and I'm talking
about streaming.

It does seem like the way for someone in my situation to
handle this--I post hundreds of videos inside membership
websites--is to give members two versions, one in lower
bitrate and one in higher, for each video.

Anybody have an opinion on that? (Of course you do! That's
why I love Muvipix!!!!!!!!!!!!!!!!! It's my lifeline.)