Hi all, I'm writing an interactive app on the N900 with PR 1.2. which captures audio and analyzes it.
I used QAudioInput and while audio capture works, is has an EXTREMELY high latency, several seconds, (around 3-5secs). I tried several sample rates, 8000, 44100, 48000 Hz, tried with small buffer sizes eg 512 samples but QAudioInput always seems to set the buffer size to about 100msec. I did take a look at the source of QAudioInput and it confirmed my findings, QAudioInput::setBufferSize() is not honored and a fixed buffer size is used instead. QAudioInput is advertised to provide a low level API to talk directly to the audio device but in it's present form it's not working as it is supposed. And even if 100msec is used as the ALSA buffer size, something fishy is going on. AFAIK pulseaudio is providing a virtual ALSA device and it could cause this big delay. The same code works on Linux where the latency is as QAudioInput sets it to around 100msecs. So the problem lies in Maemo/N900. I'm one of the authors of LinuxSampler, the most widely used open source audio sampler, http://www.linuxsampler.org and we can target all common OSes and audio interfaces (we use an abstraction layer) and we consistently achieve very low latencies on any platform, including Windows, we are talking about <5-10msec latencies. So I see no reason why QAudio* cannot achieve those numbers too. we can help out with QAudio* by providing advices, bug reports and working code implementations. I think Nokia should take the audio latency issue very seriously since without low latency a range of apps cannot be implemented and it diminishes the value of Nokia's platforms and APIs as a valid multimedia system. Nokia's losing market share is caused too by things like this, lack of attention to the detail. On the Iphone, even the most stupid developer gets this audio application working with low latency, because the API does what it advertises and Apple has paid attention to these things. I'm an audio developer that programmed on many platforms and embedded systems but newer experienced something that bad like QAudioInput on the N900. So please can you point me to an API on the N900 how I could capture audio with lower latency ? since skype runs on the N900, I know it's possible, but the docs on maemo.org don't clearly say how to do it. some on maemo irc channel said I should use the gstreamer API. Any reference what the optimal parameters are ? Some reference code or pointers to an existing open source application would be welcome. Since Nokia's goal is to push Qt as the only API to use because of it's powerful features and crossplatform capabilities, they should pay attention to make it working correctly. As other professional audio developers said too (ask anyone on the linux-audio-dev list) the decision of using pulseaudio on a phone was very bad since it was not designed with real time in mind. The most advanced audio server on Linux is currently JACK, http://www.jackaudio.org/ it has been in use by professional linux audio developers for several years and IS DESIGNED with low latency in mind. there are hardware products based on jackd and linuxsampler like the Lionstracs Mediastation which achieve 5 msec latency running the software sampler, audio streaming, video players all in parallel. I contributed to that keyboard too so I know all the complexities behind the system. But the fact is that JACK's clean design made this possible. If we would have chosen to base it on pulseaudio, the product would have been unsellable. So it is puzzling why Nokia decides to continue with pulseaudio even in Meego. Meego is the successor of Maemo so it is natural to inherit features and code from Maemo, but nowhere is it written in stone that they need to continue with pulseaudio. Nokia take a look as JACK's clean design, it was refined over several iterations, jack2 was developed as a research project at a french university and is backed by research papers and many real world apps, and it's even multi processing capable by partitioning work loads while maintaining excellent low latency. The Lionstracs keyboard makes use of it and the quadcore CPU version can process an insane amount ov voices and audio data in real time. we are talking about around 1000 voices @ 24bit 44kHz So my advice to Nokia, while still in time, cosider switching to JACK as an audio server for future versions of Meego, I still not get why big corporations like Nokia don't do their research to look what's available on the market, why chose an inferiour product and customize it and put it in their devices (N900) when there is something better around that is completely free (LGPL) and is well tested and in use by professional audio users and hardware. Sorry for the rants, and sorry for sounding perhaps a bit arrogant but I just represent a developer which is frustrated that in 2010 modern hardware cannot provide the application developer with an easy way to achieve low audio latencies and fast respose times only due to the companies not doing their homework to optimize the platform and overlooking an already working system (like JACK) and chosing to go with an inferiour product. juist read the comments on this interview with pulseaudio's developer, most comments are negative: http://www.cio.com.au/article/320807/open_source_identity_pulseaudio_creator_lennart_poettering/ I'm sbuscribed to various linux audio mailinglist and other audio forums and never heard such bad complaints about JACK for example. This says it all. I know I'm repetitive, but Nokia made a bad choice by chosing pulseaudio. I hope they still swtich their audio system in Meego, but knowing the attitude of big corporations it will be probably be like that, that since they have chosen to elect a certain app (pulseaudio) they will not change it and all bugs will be rooted out. But if the foundations are not solid, a house is never going to be stable. Sometimes it makes sense to tear it down and rebuild it from scratch. I hope that Meego will become the leading mobile platform of choice providing great end-user experience and give developers a powerful platform that is fun easy to develop for. Those problems like I have experienced on Maemo cannot happen on Meego. Developers do not tolerate platforms which don't deliver a smooth user experience with little programming effort. The mobile world has gotten very competitive and the only way to win mindshare is providing the things mentioned above, otherwise developers will switch and the platform will not gain traction.. I hope that the sharing of my experiences, my feedback and opinions ad a long time audio developer can lead to an improvement of the platform and help to root out bugs and inefficiencies. I'm open to any kind of discussion on the matter. thanks everyone for your advices, tips and contributions, regards, Benno The LinuxSampler project http://www.linuxsampler.org _______________________________________________ maemo-developers mailing list maemo-developers@maemo.org https://lists.maemo.org/mailman/listinfo/maemo-developers
