Adpcm ima4 #384
Adpcm ima4 #384
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Co-authored-by: hikari_no_yume <hikari@noyu.me>
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I am listed as a co-author here because the |
| #[rustfmt::skip] | ||
| const IMA_INDEX_TABLE: [i32; 16] = [ | ||
| -1, -1, -1, -1, 2, 4, 6, 8, | ||
| -1, -1, -1, -1, 2, 4, 6, 8, | ||
| ]; | ||
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| #[rustfmt::skip] | ||
| const IMA_STEP_TABLE: [i32; 89] = [ | ||
| 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, | ||
| 19, 21, 23, 25, 28, 31, 34, 37, 41, 45, | ||
| 50, 55, 60, 66, 73, 80, 88, 97, 107, 118, | ||
| 130, 143, 157, 173, 190, 209, 230, 253, 279, 307, | ||
| 337, 371, 408, 449, 494, 544, 598, 658, 724, 796, | ||
| 876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066, | ||
| 2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358, | ||
| 5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899, | ||
| 15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767, | ||
| ]; | ||
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| /// `AdpcmImaBlockStatus` contains values to decode a block | ||
| struct AdpcmImaBlockStatus { | ||
| predictor: i32, | ||
| step_index: usize, | ||
| } | ||
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| impl AdpcmImaBlockStatus { | ||
| fn read_preamble<B: ReadBytes>(stream: &mut B) -> Result<Self> { | ||
| let header = stream.read_be_u16()?; | ||
| let predictor = u16_to_i32!(header & 0xFF80); | ||
| let step_index = ((header & 0x7F) as usize).min(IMA_STEP_TABLE.len() - 1); | ||
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| let status = Self { predictor, step_index }; | ||
| Ok(status) | ||
| } | ||
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| fn expand_nibble(&mut self, byte: u8, nibble: Nibble) -> i32 { | ||
| let nibble = nibble.get_nibble(byte); | ||
| let step = IMA_STEP_TABLE[self.step_index]; | ||
| let sign = (nibble & 0x08) != 0; | ||
| let delta = (nibble & 0x07) as i32; | ||
| let diff = ((2 * delta + 1) * step) >> 3; | ||
| let predictor = if sign { self.predictor - diff } else { self.predictor + diff }; | ||
| self.predictor = clamp_i16(predictor) as i32; | ||
| self.step_index = self | ||
| .step_index | ||
| .saturating_add_signed(IMA_INDEX_TABLE[nibble as usize] as isize) | ||
| .min(IMA_STEP_TABLE.len() - 1); | ||
| from_i16_shift!(self.predictor) | ||
| } | ||
| } |
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Couldn't all or most of this code be shared with codec_ima.rs? The ima4 format is basically just another framing of IMA ADPCM.
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I think the tables and the nibble expansion could be shared. The preamble read definitely can't. I could consolidate if that's preferred.
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It was the table and nibbles part I had in mind, yeah, because they're from the IMA ADPCM standard.
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I refactored it a bit keeping the preamble and decoding separate with a shared expansion
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Thanks @acieslewicz and @hikari-no-yume for this, and apologies for the delay. LGTM, but since it has been a while the workflow approval has timed out. I ran the tests locally but the formatting check fails. Could you run rustfmt with |
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Done! Thanks for the review! |
Adds ima4 decoding support to adpcm. This seems to be working from my local testing. Please let me know if I missed anything or if I should make any changes!