[Speex-dev] Any tips for speeding up encoding on iPhone?

[Alex Bumbu]

Hi,

I've lowered the recording to a 16 kHz sample rate and set the encoding
quality to 8 and I've achieved a ratio around 2:1 (twice more sample
recorded than compressed), which is way better than the one for 44.1 kHz
recorded samples, but still doesn't work as I want to. If I set the
recording to 8 kHz the compression works great in real time.
The FIXED_POINT is set in the config.h. Any ideas on what settings should I
modify to improve the 16 Khz compression.

Thanks in advance,
Alex Bumbu

On Thu, Jun 2, 2011 at 7:25 PM, Alex Bumbu <alex.bumbu at gmail.com> wrote:

> Hi,
>
>
> I'm trying to use Speex for real time encoding in an iPhone project but I'm
> having latency problems. I appreciate any tips you may provide for speeding
> things up.
>
>
> The recording callback is providing 1024 samples (mono, frequency: 44100
> Hz, of type short) every 23 ms (1024.0 / 44100.0). I'm saving the samples in
> a buffer and use them in the encoding thread (set for mode: wide band - 16
> Khz), but for every frame of 320 samples it takes ~40 ms, so soon the buffer
> runs out of space and it'll start missing samples.
>
> I've tried lowering the quality and setting the recorder frequency to 16
> Khz but didn't worked.
>
> Is there any way to optimize the encoding so it can keep up with the
> recording?
>
>
> Below you can find the code I'm using. Maybe you notice some obvious
> problems.
>
>
> - (void)initSpeexEncoder {
>
>     speex_bits_init(&speexBits);
>
>     speexEncoderState = speex_encoder_init(&speex_wb_mode);
>
>
>
>     // get the frame size (expressed in samples)
>
>     speexFrameSize = 0;
>
>     speex_encoder_ctl(speexEncoderState, SPEEX_GET_FRAME_SIZE, &
> speexFrameSize);
>
>
>
>     // set quality parameter that controls the quality vs bit-rate
> tradeoff
>
>     UInt8 speexEncodingQuality = 10; // values from 0 to 10 (inclusively)
>
>     speex_encoder_ctl(speexEncoderState, SPEEX_SET_QUALITY,
> &speexEncodingQuality);
>
>
>
>     // alloc the buffer
>
>     _compressedSpeexBufferSize = 1024;
>
>     _compressedSpeexBuffer = malloc(_compressedSpeexBufferSize);
>
> }
>
>
> - (void)freeSpeexEncoder {
>
>     speex_bits_destroy(&speexBits);
>
>     speex_encoder_destroy(speexEncoderState);
>
>
>
>     free(_compressedSpeexBuffer);
>
>     _compressedSpeexBufferSize = 0;
>
> }
>
>
> - (void)encodeThread {
>
>     // alloc buffer to hold the specified amount of short type samples
>
>     short *input = malloc(speexFrameSize * sizeof(short));
>
>
>
>     while (recording) {
>
>         // proceed only if we have enough samples for a frame
>
>         if (_toCompressBuffer.size >= speexFrameSize * sizeof(short)) {
>
>
>             // fill frame with samples
>
>             //memcpy(input, _toCompressBuffer.data, speexFrameSize *
> sizeof(short));
>
>
>
>             // process one frame at a time
>
>             NSLog(@"Start encode");
>
>             speex_bits_reset(&speexBits);
>
>             //speex_encode_int(speexEncoderState, input, &speexBits);
>
>             speex_encode_int(speexEncoderState, _toCompressBuffer.data, &
> speexBits); // without using extra buffer
>
>             UInt16 nbBytes = speex_bits_write(&speexBits,
> _compressedSpeexBuffer, _compressedSpeexBufferSize);
>
> NSLog(@"Ended encode");
>
>
>
>             static int processedBytes = 0;
>
>             processedBytes += speexFrameSize * sizeof(short);
>
>             NSLog(@"Processed bytes: %d", processedBytes);
>
>
>
>             if (nbBytes) {
>
>                 // write to file
>
>                 // first write the header (2 bytes)
>
>                 // the header must contain the number of compressed bytes
> for a frame
>
>                 static bool once = NO;
>
>                 if (!once) {
>
>                     [file writeData: [NSData dataWithBytesNoCopy: &nbBytes
> length: sizeof(nbBytes)]];
>
>                     once = YES;
>
>                 }
>
>
>
>                 // write encoded data
>
>                 [file writeData: [NSData dataWithBytesNoCopy:
> _compressedSpeexBuffer length: nbBytes]];
>
>
>
>                 // remove from buffer -- one frame
>
>                 [_toCompressBuffer removeFirstBytes: speexFrameSize *
> sizeof(short)];
>
>                 NSLog(@"Stop encode frame");
>
>             }
>
>
>
>         }
>
>     }
>
>
>
>     free(input);
>
> }
>
>
> Thanks,
>
> Alex Bumbu
>
>
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