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Ancillary Data

Quadro SDI Output PG-03776-001_v06 | 37

6.4.3 Determining the Number of Audio Samples per

Frame

It is the responsibility of the application to send the required number of audio samples

per frame. Sending an insufficient number of samples will result in breaks in the audio

stream. To determine the number of required audio samples per frame for a given video

signal format and the length of the audio frame sequence, an application should use

NvVIOANCAPI_NumAudioSamples as demonstrated in the following code sample.

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Note: As specified by the SMPTE 272M and 299M specifications, 1000/1001 signal

formats have an uneven number of audio samples per frame. In this case, the

number of audio samples per frame varies over a sequence of frames and the

position of the frame as specified by the frame sequence number dictates the

number of required audio samples.

Code Listing 34: Determining Number of Audio Samples / Frame

// Determine the length of the audio sample sequence.

NvVIOANCAPI_NumAudioSamples(getHandle(),

NVVIOANCAUDIO_SAMPLING_RATE_48_0,

(NvU32 *)&m_uiSequenceLength,

NULL);

// Allocate/reallocate required memory for the array to hold the

// number of audio samples for each frame in a sequence.

if (m_uiNumAudioSamples)

free(m_uiNumAudioSamples);

m_uiNumAudioSamples = (unsigned int*)calloc((size_t)m_uiSequenceLength,

sizeof(NvU32));

// Determine number of audio samples based on signal format

// and audio sampling rate.

NvVIOANCAPI_NumAudioSamples(getHandle(),

NVVIOANCAUDIO_SAMPLING_RATE_48_0,

(NvU32 *)&m_uiSequenceLength,

(NvU32 *)m_uiNumAudioSamples);

6.4.4 Specifying Audio Data

Once the raw PCM audio data is packed as described, it is inserted into the

NVVIOANCDATAFRAME structure as shown in Code Listing 35. Each group of four audio

channels also has an associated 32-bit control value. This 32-bit variable permits the

specification of the active channels, frame numbers and other controls within the SMPTE

per-frame audio control packet that accompanies the audio data packets for the specified

audio group.

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