Audio renderer fails to render CMSampleBuffer

Question

Created Sep ’18

Replies 4

Boosts 1

Views 2.9k

Participants 3

I am trying to render audio using AVSampleBufferAudioRenderer but there is no sound coming from my speakers and there is a repeated log message.

[AQ] 405: SSP::Render: CopySlice returned 1

I am creating a CMSampleBuffer from an AudioBufferList. This is the relevant code:

var sampleBuffer: CMSampleBuffer!
try runDarwin(CMSampleBufferCreate(allocator: kCFAllocatorDefault,
                                   dataBuffer: nil,
                                   dataReady: false,
                                   makeDataReadyCallback: nil,
                                   refcon: nil,
                                   formatDescription: formatDescription,
                                   sampleCount: sampleCount,
                                   sampleTimingEntryCount: 1,
                                   sampleTimingArray: &timingInfo,
                                   sampleSizeEntryCount: sampleSizeEntryCount,
                                   sampleSizeArray: sampleSizeArray,
                                   sampleBufferOut: &sampleBuffer))

try runDarwin(CMSampleBufferSetDataBufferFromAudioBufferList(sampleBuffer,
                                                             blockBufferAllocator: kCFAllocatorDefault,
                                                             blockBufferMemoryAllocator: kCFAllocatorDefault,
                                                             flags: 0,
                                                             bufferList: audioBufferList.unsafePointer))
try runDarwin(CMSampleBufferSetDataReady(sampleBuffer))

I am pretty confident that my audio format description is correct because CMSampleBufferSetDataBufferFromAudioBufferList, which performs a laundry list of validations, returns no error.

I tried to reverse-engineer the CopySlice function, but I’m lost without the parameter names.

int ScheduledSlicePlayer::CopySlice(
   long long,
   ScheduledSlicePlayer::XScheduledAudioSlice*,
   int,
   AudioBufferList&,
   int,
   int,
   bool
)

Does anyone have any ideas on what’s wrong? For the Apple engineers reading this, can you tell me the parameter names of the CopySlice function so that I can more easily reverse-engineer the function to see what the problem is?

Boost

Answer 1

OOPer OP

Sep ’18

If your app does not stop on the message `[AQ] 405: SSP::Render: CopySlice returned 1`, it may be just a debug message inside framework and you should better ignore it and find other reasons why no sound coming.

I recommend you first to check if you really made your `audioBufferList` properly. Can you show how you made it?

0

Answer 2

fumoboy007 OP

Sep ’18

I have created a sample project that exhibits the problem. The audio plays if isInterleaved == true || channelCount == 1, but it doesn’t play otherwise. Thanks for helping!

---

I am pretty much at a dead end with reverse engineering. For posterity’s sake, here is what I found when isInterleaved == false && channelCount == 2:

ScheduledSlicePlayer::CopySlice(long long, ScheduledSlicePlayer::XScheduledAudioSlice* arg1, int, AudioBufferList& arg3, int, int, bool)
- Copies data from the AudioBufferList pointed to by arg3 into the AudioBufferList nested in arg1.
- Fails because the audio buffer count of the source AudioBufferList (2) is not equal to the audio buffer count of the destination AudioBufferList (1).
AudioQueueObject::ConvertOutput(AudioQueueObject::ConverterConnection*, AQBufferCommand* arg1, int, bool)
It initializes the destination AudioBufferList with 1 AudioBuffer when `*(int32_t *)(arg1+0x8) == 1`. arg1+0x8 is likely an enum; its type is AQCommand::ECommand.

AQBufferCommand::AQBufferCommand(AQCommand::ECommand arg0, AQBuffer*, unsigned int, AudioStreamPacketDescription const*, XAudioTimeStamp const&)
Sets *(int32_t *)(this+0x8) = arg0.
AudioQueueObject::EnqueueBuffer(AudioQueueBuffer*, unsigned int, AudioStreamPacketDescription const&, int, int, unsigned int, AudioQueueParameterEvent*, XAudioTimeStamp const&, XAudioTimeStamp *)
Calls AQBufferCommand::AQBufferCommand with arg0 = 1.

1

Answer 3

fumoboy007 OP

Oct ’18

For any Apple engineers who are reading this, I’ve filed this bug as rdar://45068930.

0

Answer 4

robnapier OP

Oct ’22

(Moving to a reply rather than a comment to be more easily found.)

I believe that interleaving is the key. I see the same symptoms on planar formats, but interleaved formats work, even for 2 channel audio. I expect this is an undocumented requirement (and an Apple bug). Tested on iOS 16.1.

0