when I play music with FMOD Ex I get a huge performance hit, CPU average load is ~20%.
In comparison, when using iPhone AudioToolbox the CPU average load is only 4% or less.
Am I doing something wrong here?
The MP3 is a 128kbps stereo file, and was tested on iPhone 3G, iPhone OS 3.1, FMOD version 42606.
[code:32c7bzsx]// Simple Mp3 music test
SAFE_FMOD( FMOD::EventSystem_Create( &m_pEventSystem ) );
SAFE_FMOD( m_pEventSystem->init( 32, FMOD_INIT_NORMAL, NULL, FMOD_EVENT_INIT_NORMAL) );
SAFE_FMOD( m_pEventSystem->getSystemObject( &m_pSystem ) );
SAFE_FMOD( m_pSystem->createStream( (m_strResourcePath+"menu.mp3").c_str(), FMOD_HARDWARE | FMOD_LOOP_OFF, NULL, &pMusicSound) );
SAFE_FMOD( m_pSystem->playSound(FMOD_CHANNEL_FREE, pMusicSound, false, &pMusicChannel) );[/code:32c7bzsx]
Thankful for answers.
- Pontus asked 8 years ago
We plan to implement hardware decoding via the AudioQueue offline decoder as an FMOD codec. There has been a few stalls getting this project started due to other higher priority commitments but we are still eager to get this done as soon as possible.
[quote="mathew":1zymu46y]The FMOD hardware AudioQueue implementation is more performant than the FMOD software codec implementations. Also for 3.0+ devices, you can have multiple AudioQueue software codecs which are also more performant than their FMOD counterparts. Additionally the AudioQueue implementation also enables support for AAC and ALAC so it will definitely be beneficial.[/quote:1zymu46y]
Are you sure you measure all CPU, not just the "user" part? Because all i see is a CPU loading shift from "user" (FMOD) to "system" (Audio Queue).
I checked many aspects of my implementation using Shark, Instruments etc., but all that CPU eating thing happens in Core Audio, not my code, and i couldn’t really optimize nothing (tried to adjust buffer sizes, etc.).
Or maybe you don’t use AudioFileReadPackets, but FMOD’s own? What’s the secret Sir?
It sounds to me like you are using the same method for implementing setPosition as us. As for performance issues, if you have any tips or tricks you would like to share we would be happy to review them for inclusion in FMOD.
Perhaps we should move this discussion to firstname.lastname@example.org?
[quote="mathew":1nrg4lu7]What method are you using to get the CPU usage results?
Our block alignment is 16384 bytes rounded down to ensure it’s a multiple of the bytes per frame size. Also yes, we are using AudioFileReadPackets.[/quote:1nrg4lu7]
I’m using top from the bash command line (the phone is jailbroken), it provides more precise results than Instruments.
Your block alignment is 16384 bytes rounded down to the frame size of the input file, the frame size of an MP3 for example?
Sorry, now i know. So you’ve 16384 rounded down to a multiple of the output bytes per frame, so it will be 16384 still for 16-bit stereo PCM.
I’ve 2 last optimization questions:
How long buffer size did you choose for packetsToRead from AudioFileReadPackets? 1 seconds, half second… ?
What’s the best format to convert to? I’m doing FMOD_SOUND_FORMAT_PCM16 (kLinearPCMFormatFlagIsPacked | kLinearPCMFormatFlagIsSignedInteger), but is it better if i choose PCMFLOAT?
I recently profiled my App that uses version FMOD 4.28.02.
And I’m really surprised by the CPU usage.
I didn’t remember having these numbers last time I checked it (with a 4.26 version).
I don’t remember changing anything on the data side or on my code.
Do you see anything I should look into ?
[quote:3n3jngdx]I’m using top from the bash command line (the phone is jailbroken), it provides more precise results than Instruments. [/quote:3n3jngdx]
Ah ok, yeah the instruments method of getting CPU seems a bit imprecise. The FMOD CPU usage measure is good but it doesn’t take into account mediaserv.
[quote:3n3jngdx]Sorry, now i know. So you’ve 16384 rounded down to a multiple of the output bytes per frame, so it will be 16384 still for 16-bit stereo PCM.[/quote:3n3jngdx]
That is correct, for 16bit stereo the size is the same, are just ensuring there is a whole number of frames in the buffer.
[quote:3n3jngdx]How long buffer size did you choose for packetsToRead from AudioFileReadPackets? 1 seconds, half second… ? [/quote:3n3jngdx]
As for read packets, we use 16k / max packet size, with a minimum of 2 packets.
[quote:3n3jngdx]What’s the best format to convert to? I’m doing FMOD_SOUND_FORMAT_PCM16 (kLinearPCMFormatFlagIsPacked | kLinearPCMFormatFlagIsSignedInteger), but is it better if i choose PCMFLOAT?[/quote:3n3jngdx]
The best format to output in is 16bit as you are doing.
Nothing has changed recently with the MP3 codec, it is decoded in software and one of the more expensive formats to choose. If the usage is too high for your app I would recommend switching to a cheaper format like ADPCM or wait until March for the hardware decoder support.
The key difference between using the native iPhone API for MP3 playback and FMOD is you are decoding the MP3 at runtime in software with FMOD, where as the iPhone API uses the hardware decoder.
We do plan to add support for the hardware decoder at some point but it has the pretty big limitation of only being able to decode one sound at a time, and that is only if the iPod isn’t already playing.
20% sounds a bit excessive to me actually, our benchmarks show for a mono MP3 the cost is about 5.6% so stereo would be around 11% as recorded by System::getCPUUsage.
AudioFileReadPackets asks for how many packets to read, we do 16k / maxPacketSize, this can give numbers like 15 for how many packets to read at a time. This is not 15 seconds though, it’s around 0.4 seconds if the sample rate were 44100Hz.
Please login first to submit.