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  1. Hi.

    When i would like to convert a video file to other format using some kind of software,
    should i choose the video bitrate/sec that is shown in the file information or
    should i choose the highest bitrate/sec that i see in the"stream statistics"option
    on VLC media player(tools option)?
    For example,while in the video file information,the bitrate/sec is 8000kb/sec,
    in VLC stream statistics(while the video is playing)the bitrate/sec(which is changed each second)sometimes is low from 8000kb/sec and sometimes higher than 8000kb/sec(sometimes double and even triple than 8000kb/sec)
    So,what bitrate/sec should i choose?

    Thanks.
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  2. The correct bitrate to re-encode depends on the format you are re-encoding to, and whether you are changing the dimensions or other properties of the video, so there is no simple answer.

    It sounds like your original file is variable bitrate -- which is more efficient than constant bitrate as it will allow the bitrate to be raised for more complex scene (fast action, lots of changing details) or lowered for simpler scenes (a static title on a plain background.)

    We might be able to give some starting parameters if you tell us what you want to convert to.

    (The user doesn't determine the decoding rate, so your title doesn't make sense, but I assume this is a translation error.)
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  3. Thanks for your reply,smrpix.
    I am new in all those technical words,so my title could be wrong,but i meant
    that there are software that you can choose the video bitrate/sec and the audio
    bitrate/sec among other(resolution,frame rate,video codec,etc.),that you can set-up
    before you makes the conversion.
    Lets say that you want to "convert" an MKV(container)video file to exactly the same MKV format as the
    original file,the same codec,the same resolution etc.(i am in purpose don't change anything,
    in order to focus only on the bitrate/sec spec.)The video bitrate is 8000kb/sec
    as it is shown in the information,but when i am watching the bitrate/sec on live(VLC statistics),the
    bitrate is changing each second and sometimes double or triple the 8000kb/sec.
    I understand the meaning of this variable bitrate while watching the movie,but what
    i am trying to figure out is if to use the 8000kb/sec as it is shown in the information
    or i better choose higher bitrate in order to maintain good quality in the moments that the bitrate/sec
    is higher than 8000kb/sec?
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  4. If I am understanding your question correctly:

    Any time you re-encode you lose quality, so a higher bitrate usually means less loss.
    Whether or not 8Mbs sets a hard limit depends on whether your encoder sets that as a ceiling or an average.

    Different encoders work differently. You're asking for a general answer to a question that is determined by specifics.
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  5. Originally Posted by smrpix View Post
    ... whether your encoder sets that as a ceiling or an average...
    I think that this sentence of your reply may lead to the answer.
    When i look at the information of the video file and i see 8M bitrate/sec,
    is it the average?
    And if it is the average indeed and i choose this 8M bitrate in the encoder,
    Does the encoder(while encoding)decides when to increase bitrate
    and when to decrease bitrate refer to the average 8M bitrate the same as in the original video file?
    Since you mentioned,that the behavior of the encoder depeneds whether it designed to set
    that 8M bitrate as ceiling or an average bitrate/sec,i would like to described what happened
    when i used higher average bitrate.When i chose 16M bitrate/sec(instead 8M)in the encoder option,the file size was doubled and when i watched the bitrate/sec on live(VLC statistics),the variable bitrate/sec spikes became much higher compare to the original file(on live).
    Does it mean that the encoder,in my case,is set do see the average bitrate (not
    as ceiling)?and if i encoding with 8M bitrate/sec the new file should variable on
    live the same(more or less)as the original?
    Last edited by xchcui; 14th Sep 2020 at 11:13.
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  6. Originally Posted by xchcui View Post
    When i chose 16M bitrate/sec(instead 8M)in the encoder option,the file size was doubled
    That's the very definition of bitrate

    Code:
    average_bitrate = size / running_time
    If you're encoding with x264 or x265 I suggest you forget about bitrate and use CRF encoding. With that you pick the quality you want and the encoder uses whatever bitrate is necessary to deliver that quality. Try CRF values between about 16 and 20 if you're looking for good quality.

    In general, with bitrate based encoding you know what the size will be but you don't know what the quality will be. With quality based encoding you know what the quality will be (relative to the source, it can't make bad video look better) but you don't now the size.
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  7. Hi jagabo.

    I have tried it once or twice the quality based encoding,but it takes too much memory
    and i prefer to know what will be the ending file size.
    The point that i am trying to figure out is:if i take the same bitrate/sec as it is shown in the
    information of the original video file and i encode this video with an encoder that see this
    bitrate as an average,shouldn't the quality be more or less the same?besides the facts,that there
    will be always some lost of quality when encoding.
    BTW,yes i use x264,this is the most common encoder.
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  8. Using the same bitrate, the quality will always be worse because you are recompressing (and re-calculating) an already compressed image.

    And why do it? If you want a file the same size, just make a copy and there will be no quality loss.
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  9. Originally Posted by xchcui View Post
    I have tried it once or twice the quality based encoding,but it takes too much memory
    It doesn't take a any more memory that bitrate based encoding.

    Originally Posted by xchcui View Post
    and i prefer to know what will be the ending file size.
    You prefer knowing the size to knowing the quality? Size (bitrate) only matters if you need to fit the video on a disc (CD, DVD, BD) or when streaming over the internet.

    Originally Posted by xchcui View Post
    The point that i am trying to figure out is:if i take the same bitrate/sec as it is shown in the
    information of the original video file and i encode this video with an encoder that see this
    bitrate as an average,shouldn't the quality be more or less the same?
    With lossy codecs the quality will always be worse. Details that were lost in the first encoding will not come back. Artifacts created by the first encoding (DCT blocking, DCT ringing, etc.) are seen as "details" by the new encoder. It will waste bitrate trying to retain them. New artifacts will be created by the new encoder, and will be added to those of the first encoding. How much quality is lost depends on the encoder, settings, and bitrate.
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  10. Originally Posted by smrpix View Post
    Using the same bitrate, the quality will always be worse because you are recompressing (and re-calculating) an already compressed image.

    And why do it? If you want a file the same size, just make a copy and there will be no quality loss.
    Yes i understand,but i am trying to understand the principle of the encoding.
    If i use the bitrate/sec from the information of the original video file to
    encode a new file,let say 8Mb/sec,the quality of the new video will be less than the original.
    (even though i used the same bitrate),but if i will use an higher bitrate,let say 10Mb/sec,
    will the quality be better than the 8Mb/sec?
    Again,i understand that choosing higher bitrate won't make the video quality better
    than the original video,but i would like to know if choosing higher bitrate(for example:10Mb/sec)than in
    the original video information(8Mb/sec)can give me a better quality result?
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  11. Once again, any time you (re)encode a video with a lossy codec you will lose quality. The more bitrate you use the less quality you will lose. So yes, reencoding your 8 Mb/s video at 10 Mb/s will give higher quality than reencoding at 8 Mb/s. Both videos will be lower quality than the original 8 Mb/s video.
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  12. Originally Posted by jagabo View Post
    Once again, any time you (re)encode a video with a lossy codec you will lose quality. The more bitrate you use the less quality you will lose. So yes, reencoding your 8 Mb/s video at 10 Mb/s will give higher quality than reencoding at 8 Mb/s. Both videos will be lower quality than the original 8 Mb/s video.
    Okay,jagabo,your last post conclude this issue.
    Thank you very much for your help and for your explanation about
    this issue and thanks,also,to you smrpix
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  13. Originally Posted by jagabo View Post
    Once again, any time you (re)encode a video with a lossy codec you will lose quality. The more bitrate you use the less quality you will lose. So yes, reencoding your 8 Mb/s video at 10 Mb/s will give higher quality than reencoding at 8 Mb/s. Both videos will be lower quality than the original 8 Mb/s video.
    One more thing to verify things,how much it will be enough to increase the bitrate/sec more than the original one(in percentage)to get it close to the original quality(yes,i didn't forget,it will still be lower quality than the original)125%,150%,200%?
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  14. How close is close? The answer is different for different people. The answer is different for different videos. The answer is different for different codecs. The answer is different for different settings, even if you're using the same encoder. The answer is different if your filtering the video in any way.
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  15. I understand.I thougth that there is a rule of thumb or something for that.
    Okay.Thanks again jagabo.
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  16. The rule of thumb is to use crf encoding so you always get exactly the right bitrate for the quality you want.
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  17. Yes,after checking all the options,
    it probably the right way to do it.
    Thanks again.
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