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  1. Member
    Join Date: Jan 2014
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    Hi,

    Amazon VOD publishes they use a bit rate of 2.5 Mbps for their HD 720p content.


    When I capture at 2.5 Mbps (MP4: h.264 and AAC) I can see obvious pixelation. If I bump up the bit rate to 5.0 Mbps, it is much cleaner.


    I am trying to understand why the 2.5 is not adequate. Being a noob, I would expect it to be an exact replica of the stream.


    I am guessing, re-encoding an already compressed stream is the culprit. If that is the case, what bit rate do I have to use in order to maintain 99% of the quality of the stream?


    Thanks!
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  2. Member
    Join Date: Mar 2008
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    They have streaming to worry about, so they settled on a (relatively) low Mbps.
    Perhaps they soften the image a little to get away with it.

    What are you trying to do with this stream ?
    "I am trying to understand why the 2.5 is not adequate" - adequate for what?
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  3. Member
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    I am capturing the stream (MP4 - h.256 AAC).

    When i configure the capture, setting the bit rate at 2.5 Mbps (which is Amazon's published bit rate) results in a much poorer quality than what the original stream looks like.

    I would like to maintain the original quality of the stream. I want to know what he minimum bit rate is that I can do that with.

    As a general noob question, if i re-encode a video with the exact same parameters as it was originally encoded with do I lose quality?
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  4. Member
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    Every time video is re-encoded, there is some quality loss regardless of the settings.
    How are you capturing the stream? Can you not capture it in its original form?

    Isn't Amazons stream DRM protected? Please explain your process.
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  5. Member
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    I am capturing output from my PS4 using an avermedia extreme cap u3 unit.

    I have amazon app installed on PS4.

    Not doing anything to bypass DRM, I plugged my PS4 into the avermedia unit and it just works.
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  6. I'm a Super Moderator johns0's Avatar
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    Capture at a higher bitrate and then re-encode to 2.5mbps using 2 pass,you will get much better results than capturing at 2.5 mbps.
    I think,therefore i am a hamster.
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  7. Member
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    Originally Posted by comp1mp View Post
    I am capturing output from my PS4 using an avermedia extreme cap u3 unit.

    I have amazon app installed on PS4.

    Not doing anything to bypass DRM, I plugged my PS4 into the avermedia unit and it just works.
    OK. SO you have an HDMI connection, and your re-compressing during the capture.

    It's difficult to recommend a specific bitrate, so much depends on the material being captured.
    For example, the video complexity, sharpness, noise, etc,etc.
    So mach better if the software , instead of a bitrate setting, had a quality setting.

    For example, H.264, use Constant Rate Factor - then you get the specific quality you ask for, and the
    resulting bitrate achieved is a secondary consideration.

    Does your capture software offer a "quality" setting, Vs. hard coded bitrate?

    Perhaps as an experiment you should consider capturing a small sample at a high bitrate (say 10mbps)
    and then re-encoding in Ripbot264 or Handbrake using one of the presets. Would offer you many more options.

    There may be some others in the forum who may have specific experience re: this kind of capture
    and may offer some alternate suggestions.
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  8. 1) Hardware AVC encoders aren't as good as software AVC encoders. So they'll need more bitrate right off the bat.

    2) If you're capturing 720p from a game console it's 720p at 60 fps. Movies from Amazon are at 24 fps. More fps means more bitrate is required.

    3) Different videos require different amounts of bitrate. The more motion, grain, etc., the more bitrate you need.
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  9. Member
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    Thanks to all.

    This unit actually is a software based encoder.

    There is not a quality setting, however it can capture 1080p 60fps at 30 Mbps.

    I will capture using max settings and then re-encode as suggested.
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  10. Originally Posted by comp1mp View Post
    This unit actually is a software based encoder.
    Realtime software encoders are even worse than hardware encoders. They take all kinds of shortcuts in order to encode quickly.
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  11. Member
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    Originally Posted by jagabo View Post
    Originally Posted by comp1mp View Post
    This unit actually is a software based encoder.
    Realtime software encoders are even worse than hardware encoders. They take all kinds of shortcuts in order to encode quickly.
    What is the difference between a "realtime software encoder" and a "software AVC encoder"?
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  12. Member
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    Realtime encoder encodes during the capture - time is of the essence; any delays = dropped frames.

    Regular encoders, from a source already on your PC, can take as long as it wants, the next frame will always be there,
    no matter how slow the encode goes.
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  13. Member
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    Originally Posted by davexnet View Post
    Realtime encoder encodes during the capture - time is of the essence; any delays = dropped frames.

    Regular encoders, from a source already on your PC, can take as long as it wants, the next frame will always be there,
    no matter how slow the encode goes.
    OK, then I think the extreme cap is a "software avc encoder". It is USB 3.0 hardware which I believe acts as a buffer, but does not have a dedicated hardware encoding chip.
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  14. Banned
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    Originally Posted by comp1mp View Post
    Hi,

    Amazon VOD publishes they use a bit rate of 2.5 Mbps for their HD 720p content.


    When I capture at 2.5 Mbps (MP4: h.264 and AAC) I can see obvious pixelation. If I bump up the bit rate to 5.0 Mbps, it is much cleaner.
    It is in fact about 2500K for the video portion, and 128K for the AAC audio. I just checked four files of content I purchased on Amazon, and the video bit rate for all of them is 2498K. This is for avc/aac file saved right off the flash player. I understand they send you higher bit rate WMV files for purchased content that you download through their unbox download option.
    Last edited by blimey; 14th Jan 2014 at 02:50.
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