Must set 'SampleDescriptionExtensionAtoms' for 'extensions', 'SampleDescriptionExtensionAtoms' must contain 'av1C' for av1 extradata, example: { mediaType:'vide' mediaSubType:'av01' mediaSpecific: { codecType: 'av01' dimensions: 720 x 1280 } extensions: {{ BitsPerComponent = 8; CVFieldCount = 1; CVImageBufferChromaLocationBottomField = Left; CVImageBufferChromaLocationTopField = Left; CVImageBufferColorPrimaries = "ITU_R_709_2"; CVImageBufferTransferFunction = "ITU_R_709_2"; CVImageBufferYCbCrMatrix = "ITU_R_709_2"; Depth = 24; FormatName = "'av01'"; FullRangeVideo = 0; RevisionLevel = 0; SampleDescriptionExtensionAtoms = { av1C = {length = 20, bytes = 0x81050c000a0e0000002cd59f3fddaf9901010104}; }; SpatialQuality = 0; TemporalQuality = 0; VerbatimISOSampleEntry = {length = 124, bytes = 0x0000007c 61763031 00000000 00000001 ... 000a6669 656c0100 }; Version = 0; }} }