Function: extractCta608DataFromAv1Sample()

function extractCta608DataFromAv1Sample(
   raw, 
   startPos, 
   sampleSize
): number[][];

Defined in: extractCta608DataFromAv1Sample.ts:29

Extracts CTA-608 data from an AV1 (av01) sample.

AV1 has no NAL units, so captions ride in an metadata_itu_t_t35 OBU rather than in an SEI message. The caption payload is unchanged — the same A/53 cc_data() under the same T.35/GA94 identifier that extractCta608DataFromSample reads — so the returned field data feeds Cta608Parser identically.

This is a separate function rather than a codec branch inside extractCta608DataFromSample because the two carriages are framed differently and neither sample is self-identifying. A NAL unit sample puts a fixed-width big-endian length in front of each unit, and that width is only known from lengthSizeMinusOne in the avcC/hvcC config. An AV1 sample uses the low-overhead format, where each OBU carries its own obu_size after the header — and may omit it on the last OBU. Select on the sample entry type (av01) instead.

Parameters

raw

DataView

The DataView with media data

startPos

number

The start position of the sample within the DataView

sampleSize

number

The size of the sample in bytes

Returns

number[][]

fieldData array containing field 1 and field 2 data arrays

Example

it('should extract CTA-608 field data from an AV1 metadata OBU', async () => {
	const file = await readFile(new URL('./fixtures/608_av1.mp4', import.meta.url))
	const { view, mdatBodyStart, samples } = parseSegment(file)

	// The first sample carries the RCL control pair that opens the caption
	const fieldData = extractCta608DataFromAv1Sample(view, mdatBodyStart, samples[0].size)

	deepEqual(fieldData, [[0x94, 0x20], []])
})