| Bring vidya in cfd3e36 nandi 19d ago | 1 | //! AVCC (length-prefixed) → Annex B converter for H.264-in-MP4. |
| 2 | //! |
| 3 | //! Adapted from the `openh264` crate's `examples/mp4` helper (BSD-2-Clause). |
| 4 | |
| 5 | use mp4::Mp4Track; |
| 6 | |
| 7 | /// Network abstraction layer type for an H.264 NAL unit. |
| 8 | #[derive(Debug, Clone, Copy, PartialEq, Eq)] |
| 9 | enum NalType { |
| 10 | Unspecified = 0, |
| 11 | Slice = 1, |
| 12 | IdrSlice = 5, |
| 13 | Sps = 7, |
| 14 | Pps = 8, |
| 15 | Other, |
| 16 | } |
| 17 | |
| 18 | impl From<u8> for NalType { |
| 19 | fn from(value: u8) -> Self { |
| 20 | match value & 0x1F { |
| 21 | 0 => Self::Unspecified, |
| 22 | 1 => Self::Slice, |
| 23 | 5 => Self::IdrSlice, |
| 24 | 7 => Self::Sps, |
| 25 | 8 => Self::Pps, |
| 26 | _ => Self::Other, |
| 27 | } |
| 28 | } |
| 29 | } |
| 30 | |
| 31 | struct NalUnit<'a> { |
| 32 | nal_type: NalType, |
| 33 | bytes: &'a [u8], |
| 34 | } |
| 35 | |
| 36 | impl<'a> NalUnit<'a> { |
| 37 | fn from_stream(mut stream: &'a [u8], length_size: u8) -> Option<(Self, &'a [u8])> { |
| 38 | if stream.len() < length_size as usize { |
| 39 | return None; |
| 40 | } |
| 41 | let mut nal_size = 0u32; |
| 42 | for _ in 0..length_size { |
| 43 | nal_size = (nal_size << 8) | u32::from(stream[0]); |
| 44 | stream = &stream[1..]; |
| 45 | } |
| 46 | if nal_size == 0 || stream.len() < nal_size as usize { |
| 47 | return None; |
| 48 | } |
| 49 | let packet = &stream[..nal_size as usize]; |
| 50 | let nal_type = NalType::from(packet[0]); |
| 51 | let unit = NalUnit { |
| 52 | nal_type, |
| 53 | bytes: packet, |
| 54 | }; |
| 55 | stream = &stream[nal_size as usize..]; |
| 56 | Some((unit, stream)) |
| 57 | } |
| 58 | } |
| 59 | |
| 60 | /// Convert MP4/AVCC length-prefixed NAL units to Annex B for OpenH264. |
| 61 | /// |
| 62 | /// Also injects SPS/PPS from the `avcC` box when an IDR arrives without them. |
| 63 | pub struct Mp4BitstreamConverter { |
| 64 | length_size: u8, |
| 65 | sps: Vec<Vec<u8>>, |
| 66 | pps: Vec<Vec<u8>>, |
| 67 | new_idr: bool, |
| 68 | sps_seen: bool, |
| 69 | pps_seen: bool, |
| 70 | } |
| 71 | |
| 72 | impl Mp4BitstreamConverter { |
| 73 | pub fn for_mp4_track(track: &Mp4Track) -> Result<Self, String> { |
| 74 | let avcc_config = &track |
| 75 | .trak |
| 76 | .mdia |
| 77 | .minf |
| 78 | .stbl |
| 79 | .stsd |
| 80 | .avc1 |
| 81 | .as_ref() |
| 82 | .ok_or_else(|| "Track does not contain AVC1/avcC config".to_string())? |
| 83 | .avcc; |
| 84 | |
| 85 | Ok(Self { |
| 86 | length_size: avcc_config.length_size_minus_one + 1, |
| 87 | sps: avcc_config |
| 88 | .sequence_parameter_sets |
| 89 | .iter() |
| 90 | .cloned() |
| 91 | .map(|v| v.bytes) |
| 92 | .collect(), |
| 93 | pps: avcc_config |
| 94 | .picture_parameter_sets |
| 95 | .iter() |
| 96 | .cloned() |
| 97 | .map(|v| v.bytes) |
| 98 | .collect(), |
| 99 | new_idr: true, |
| 100 | sps_seen: false, |
| 101 | pps_seen: false, |
| 102 | }) |
| 103 | } |
| 104 | |
| 105 | pub fn convert_packet(&mut self, packet: &[u8], out: &mut Vec<u8>) { |
| 106 | let mut stream = packet; |
| 107 | out.clear(); |
| 108 | |
| 109 | while !stream.is_empty() { |
| 110 | let Some((unit, remaining_stream)) = NalUnit::from_stream(stream, self.length_size) |
| 111 | else { |
| 112 | break; |
| 113 | }; |
| 114 | stream = remaining_stream; |
| 115 | |
| 116 | match unit.nal_type { |
| 117 | NalType::Sps => self.sps_seen = true, |
| 118 | NalType::Pps => self.pps_seen = true, |
| 119 | NalType::IdrSlice => { |
| 120 | if !self.new_idr && unit.bytes.len() > 1 && unit.bytes[1] & 0x80 != 0 { |
| 121 | self.new_idr = true; |
| 122 | } |
| 123 | if self.new_idr && !self.sps_seen && !self.pps_seen { |
| 124 | self.new_idr = false; |
| 125 | for sps in &self.sps { |
| 126 | out.extend([0, 0, 1]); |
| 127 | out.extend(sps); |
| 128 | } |
| 129 | for pps in &self.pps { |
| 130 | out.extend([0, 0, 1]); |
| 131 | out.extend(pps); |
| 132 | } |
| 133 | } |
| 134 | if self.new_idr && self.sps_seen && !self.pps_seen { |
| 135 | for pps in &self.pps { |
| 136 | out.extend([0, 0, 1]); |
| 137 | out.extend(pps); |
| 138 | } |
| 139 | } |
| 140 | } |
| 141 | _ => {} |
| 142 | } |
| 143 | |
| 144 | out.extend([0, 0, 1]); |
| 145 | out.extend(unit.bytes); |
| 146 | |
| 147 | if !self.new_idr && unit.nal_type == NalType::Slice { |
| 148 | self.new_idr = true; |
| 149 | self.sps_seen = false; |
| 150 | self.pps_seen = false; |
| 151 | } |
| 152 | } |
| 153 | } |
| 154 | } |