VideoHelp Forum


Try DVDFab Video Downloader and rip Netflix video! Or Try DVDFab and copy Blu-rays! or rip iTunes movies!
+ Reply to Thread
Results 1 to 6 of 6
Thread
  1. Member
    Join Date
    Jan 2021
    Location
    Unknown
    Search Comp PM
    I need to burn a video to a 4.37GB DVD-5, and I want the lowest AC3 bitrate I can use without losing that much quality. I don't know the difference in efficiency between Opus and AC3, but I figure either a 256kbps or 384kbps AC3 should be comparable to a 116kbps Opus, right? This is stereo not multichannel btw.
    Quote Quote  
  2. Member
    Join Date
    Mar 2008
    Location
    United States
    Search Comp PM
    Use your ears, I used to use 256kbps.

    The audio has already taken a loss by it's conversion to aac from whatever the original source was;
    you're just trying to preserve what is left there
    Quote Quote  
  3. The bitrate of the original audio is pretty much irrelevant. The source audio is decoded, effectively as a 16 bit, 24 bit or 32 bit wave file (depending on the program doing the decoding) and that's all the encoder sees. It has no idea what the source was, so the bitrate you choose is really only related to the quality of the (re)encode, regardless of the source.

    192 kbps would probably be fine, but of course use a higher bitrate if quality is the priority. If my math is correct an hour at 192 kbp2 would result in a roughly 76MB file, and at 256kbps it'd be 115MB. Compared to the size of the video stream, the difference doesn't matter.
    Quote Quote  
  4. Member
    Join Date
    Jan 2021
    Location
    Unknown
    Search Comp PM
    Originally Posted by hello_hello View Post
    The bitrate of the original audio is pretty much irrelevant. The source audio is decoded, effectively as a 16 bit, 24 bit or 32 bit wave file (depending on the program doing the decoding) and that's all the encoder sees. It has no idea what the source was, so the bitrate you choose is really only related to the quality of the (re)encode, regardless of the source.

    192 kbps would probably be fine, but of course use a higher bitrate if quality is the priority. If my math is correct an hour at 192 kbp2 would result in a roughly 76MB file, and at 256kbps it'd be 115MB. Compared to the size of the video stream, the difference doesn't matter.
    Well technically I could just ditch AC3 and go with 1536kbps PCM, which would guarantee me the least amount of generation loss. However I'm encoding to fit on a single-layer DVD which is only 4.37GB, and since I'm using MPEG2 I want my video bitrate as high as possible; so I'd like my audio bitrate to be as low as possible while still being comparable to the source Opus track. I know that AC3 is noticeably less efficient than Opus, so I think 192kbps would still be worse than the 116kbps Opus; similar to how a 320kbps MP3 track is worse than a 256kbps AAC track. Ultimately it's not that important and I think 256kbps will be fine, I just made this post in-case someone here knew the efficiency differences between Opus and AC3.
    Quote Quote  
  5. For the LAME MP3 encoder, the -V2 variable bitrate preset is considered "transparent", and it probably "averages" around 192 kbps for stereo music. Maybe a bot more, but the consensus seems to be.... increasing the bitrate beyond -V2 really only uses more bits.
    http://wiki.hydrogenaud.io/index.php?title=LAME#Recommended_encoder_settings

    A good AAC encoder such as QAAC (it uses the Apple ACC encoding engine) probably hits "transparent" at around 128 kbps, but they're not all created equally, and for the open source AC3 encoder (are you encoding with ffmpeg or aften?) my understanding is the encoder was created from scratch to output spec compliant AC3, but it's probably not capable of the quality of the Dolby encoder at the same bitrate, as the Dolby encoder probably has additional compression tricks up it's sleeve, so for open source AC3 encoding I'd lean towards higher bitrates. Not that I really know anything about the AC3 encoder, as if I re-encode it almost always as AAC, but I don't have to worry about DVD compliance.
    Quote Quote  
  6. Member
    Join Date
    Jan 2021
    Location
    Unknown
    Search Comp PM
    Originally Posted by hello_hello View Post
    For the LAME MP3 encoder, the -V2 variable bitrate preset is considered "transparent", and it probably "averages" around 192 kbps for stereo music. Maybe a bot more, but the consensus seems to be.... increasing the bitrate beyond -V2 really only uses more bits.
    http://wiki.hydrogenaud.io/index.php?title=LAME#Recommended_encoder_settings

    A good AAC encoder such as QAAC (it uses the Apple ACC encoding engine) probably hits "transparent" at around 128 kbps, but they're not all created equally, and for the open source AC3 encoder (are you encoding with ffmpeg or aften?) my understanding is the encoder was created from scratch to output spec compliant AC3, but it's probably not capable of the quality of the Dolby encoder at the same bitrate, as the Dolby encoder probably has additional compression tricks up it's sleeve, so for open source AC3 encoding I'd lean towards higher bitrates. Not that I really know anything about the AC3 encoder, as if I re-encode it almost always as AAC, but I don't have to worry about DVD compliance.
    Oh my bad, I forgot to mention that I'm using Adobe Audition CC 2017; which I believe is the last version to still use the official Dolby encoder but I'm not sure.
    Quote Quote  



Similar Threads