[Speex-dev] Encoding/Decoding doubts
dsrosado at gmail.com
Thu Jul 16 11:22:30 PDT 2009
Flash documentation says that when using speex codec, the sample rate by
default is 16KHz. Although, it can be changed to 8KHz for example.
I thought that the number of bits per sample was determined by the sample
rate and the quality value.
Yes, i'm using 1 frame per packet.
Are you sure that i don't need to be careful with the first byte? Should i
include it anyway? I was told that i need to set it, how does flash player
know that encoding of those packets if the stream is created by the server?
Assuming that i really need to use 16KHz, 16bit, mono frames, and that i'm
getting 8KHz, 8bits mulaw/alaw data and then decoding it to linear pcm
(8KHz, 16bits), do you know if it's possible to encode it in 16KHz, 16bit
On Thu, Jul 16, 2009 at 7:05 PM, Jozsef Vass <jozsef_vass at yahoo.com> wrote:
> Flash player encodes speex at 16 kHz, mono, 16 bit. Fields
in the format byte should be ignored if the format is speex. You can set the
> quality by Microphone.encodeQuality (default 6). You can also set the number
> of speex frames per tc message using Microphone.framesPerPacket.
> Flash player can only decode speex at 16 kHz, so make sure you have the
> proper sample rate.
> > Message: 2
> > Date: Sun, 12 Jul 2009 18:36:28 +0100
> > From: Daniel Rosado <dsrosado at gmail.com>
> > Subject: [Speex-dev] Encoding/Decoding doubts
> > To: speex-dev at xiph.org
> > Message-ID:
> > <8e6ec0160907121036q29a45285x7964fcb5c6cace2b at mail.gmail.com>
> > Content-Type: text/plain; charset="iso-8859-1"
> > Hi,
> > I'm doing a VoIP related project where at some point i need
> > to decode speex
> > data gathered from a flash client, and then encode it to
> > ulaw or alaw pcm so
> > i can send it in rtp packets.
> > On the other way, i get rtp packets with ulaw and alaw pcm
> > data, then i need
> > to decode them to linear pcm and feed the speex encoder, so
> > i can send the
> > data to the flash player.
> > I'm using JSpeex, i know this is not JSpeex mailing list
> > but i would really
> > apreciate some help.
> > There are some (a lot of) things i don't understand:
> > -In flash, i can set the sample rate and the quality of the
> > speex data. If
> > the sample rate is 16KHz, the number of bits per sample,
> > and consequently
> > the bitrate, will depend on the quality.
> > After i get the speex frame, i call init on the Decoder.
> > There, i don't
> > understand what is the meaning of the sample rate if you
> > already have to
> > pass the mode. How is it related?
> > Does the speex frame contain any info about the bitrate?
> > -I know that every flash packet has a header containing
> > info about the audio
> > format, stereo or mono, bitrate, etc. But it seems to
> > change over time...For
> > example, the number of channels.
> > -After decoding a speex frame, i'm supposed to get linear
> > pcm at what sample
> > rate? The same as defined on the init? What about the
> > number of bits per
> > sample?
> > -On the speex encoding part, the parameters needed on init
> > are related to
> > the linear pcm frame i should pass to processData and it
> > also indicates what
> > type of speex frame i will get?
> > What kind of pcm data can i use to feed the encoder?
> > Maybe some of the questions don't make much sense, but i
> > can't get much info
> > on the subject.
> > Thanks in advance,
> > John
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