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https://repost.aws/questions/QUWgQdtaGsTfCUtXkQKdA1FA/dash-outputs-with-qvbr-always-exhaust-the-maximum-bit-rate-allowed https://docs.aws.amazon.com/mediaconvert/latest/ug/how-automated-abr-works.html
as per refs above
The DASH manifest specifies a bandwidth attribute in the Representation tag, which might be interpreted by some players as the "actual" bitrate. However, this value might not reflect the true average bitrate of the segments, but rather a maximum allowable value. This could be why you're seeing the bandwidth values as being double your set max bitrate in the DASH manifest and in the players that you're using.
In the automated ABR settings of MediaConvert, the "Max ABR bitrate" is meant to be an upper limit for the bitrate of the highest-bitrate rendition. If MediaConvert can achieve the same video quality at a lower bitrate, it will use that lower bitrate for your highest-quality rendition. However, it seems like this "Max ABR bitrate" may be represented in the DASH manifest as the max allowable bitrate for a given Representation, and some players may interpret this as the "actual" bitrate.
Furthermore, MediaConvert encodes all renditions with QVBR (Quality Variable Bit Rate) mode. In this mode, the bitrate can vary to achieve a given quality level, but it should not exceed the max bitrate. However, because QVBR is a variable bitrate method, the actual average bitrate of the segments may end up being lower than the max bitrate, especially if the same quality can be achieved at a lower bitrate.
As a result, you might find that the actual average bitrate of your video segments (as measured over the length of the segments) is lower than the value indicated in the DASH manifest and reported by the players.
You could verify this by examining the size and duration of your video segments to calculate the actual average bitrate, and see if it matches your expectations based on the max bitrate setting in MediaConvert.
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Thanks for the insights Sedat. I understand all the aspects about averages being less than max and qvbr reducing or increasing bitrate as needed based on content. But, the issue here is that the maximum bitrate setting under automated ABR is supposed to be just that --- maximum. Ie, there is no reason or explanation I see for the manifest to report any bandwidth higher than the absolute maximum br setting (and why always exactly 2x ??). The whole point for setting a maximum bitrate is to allow QVBR to do its thing but constrain it to that max limit, so that targeted users will never need to handle a bitrate, even for short periods, that is higher than the max that I specify... seems pointless if it does not actually serve that purpose. I could understand the manifest showing a different LOWER bitrate, such as a lower bitrate that represents an average, but never a value higher than max. Also, as I mentioned, when I set renditions manually (without auto-ABR) I still use QVBR with a max bitrate setting, and in that case the dash manifest bandwidth DOES exactly match the max bitrate setting, as I would expect -- so this leads me to believe there is something not quite right with what "automated ABR" is doing here... And I'm not sure how I would measure the actual "max" bit rate limit during playback since the max bitrate only occurs for short periods and is masked by the segmented file downloads that occur in periodic chunks at whatever mbps the network allows.