Re: Bytes Per Packet, Frames Per Packet?
Re: Bytes Per Packet, Frames Per Packet?
- Subject: Re: Bytes Per Packet, Frames Per Packet?
- From: Kyle Sluder <email@hidden>
- Date: Fri, 6 Mar 2009 15:48:52 -0500
On Fri, Mar 6, 2009 at 1:43 PM, William Stewart <email@hidden> wrote:
> If mBytesPerPacket is zero it means that every discreet packet of audio data
> (think of an AAC or MP3 encoded frame) can be a different size in bytes -
> this is the normal definition of VBR compressed audio (the same number of
> sample frames per packet, but a variable number of bytes per packet)
Okay, I'm with you so far.
> If mFramesPerPacket is zero, then it means that each audio packet can
> represent a variable duration - that is, a given audio packet can represent
> a different number of sample frames. The Vorbis format uses this
So this is another definition of VBR, or another way of organizing
compressed audio data entirely? Does mFramesPerPacket == 0 imply
mBytesPerPacket != 0?
> When you are dealing with variable data size or samples, then you have to
> represent these values with external information - that is what the packet
> descriptions are provided for. In the packet descriptions a value of zero
> means that that field is ignored (so, an AAC packet description will specify
> N for the numBytesPerPacket, and 0 for the numFrames, because AAC provides a
> constant frames per packet value)
Keeping with your AAC example: the audio stream description (a
property of the audio file) will have a non-zero mFramesPerPacket and
a zero mBytesPerPacket for an AAC file, but each packet description
will have the opposite?
Thanks,
--Kyle Sluder
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Coreaudio-api mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden