Quiet Frame Decompress: Difference between revisions
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Tag: Reverted |
Tag: Manual revert |
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=Edit to Here= | =Edit to Here= | ||
==Read Subframe== | ==Read Subframe== | ||
Revision as of 19:08, 17 March 2025
| EditDate | 2025-03-16 |
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Related Threads: FLAC Agent Build
Page created to understand how fLaC decompresses the 0 Quiet Frame so it can be incorporated into analAI
Key differences:
- Mid-side compression
Could well be the key
lossless transformation mid = (left + right)/2 and side = left − right.Web References https://www.reddit.com/r/audioengineering/comments/u2t2o4/questions about the way flac works relatively/
Issues:
- Warmup does not appear in wave or raw file which I don't understand as I get the same warmup values in analAI as FLaC seems to produce.
Seems I may have to include additional step for mid side channel de-correlation. lossless transformation mid = (left + right)/2 and side = left − right. [1]. One sure issue with this is the side channel requires an extra bit (25 vs 24) which might explain the missed warmup values but right now I don’t think so. Either way it needs to be fixed.
Instruction trace flac for analQuiet.flac
Skip metadata not pertinent [2]
Sync Frame
| Line Number | Code Package | Module | Value | Opertion Description |
|---|---|---|---|---|
| 1047 | SDC | Find Metadata | 0xFFF8 | FLAC__STREAM_DECODER_SEARCH_FOR_FRAME_SYNC FFF8 |
| 1071 | SDC | stream decoder process | 0xFFF8 | FLAC__stream_decoder_process_until_end_of_stream |
| 2041 | SDC | read_frame | Unk | read_frame_(FLAC__StreamDecoder *decoder, FLAC__bool *got_a_frame, FLAC__bool do_full_decode) |
| 350 | BRC | FLAC__bitreader_reset_read_crc16 | Unk | (FLAC__BitReader *br, FLAC__uint16 seed) |
| 2277 | SDC | read_frame_header_ | Unk | read_frame_header_(FLAC__StreamDecoder *decoder)byte. |
| 381 | BDC | FLAC__bitreader_is_consumed_byte_aligned | 0 | (const FLAC__BitReader *br) |
| 2319 | SDC | read in the raw header as bytes so we can CRC it, and parse it on the way | if(!FLAC__bitreader_read_raw_uint32(decoder->private_->input, &x, 8)) | |
| 418 | BDC | FLAC__bitreader_read_raw_uint32 | variables below | (FLAC__BitReader *br, FLAC__uint32 *val, uint32_t bits) |
Read Frame Sync Fixed Header Channel Side
Starting at 0x_1192 FFF8 C38C
& value 007F
- 0b_1111 1111 1111 10 Frame Header sync'. 14 bits
- 0b_0 mandatory 0 value Validation Bit 15
- 0b_0 0 = fixed blocking strategy Fixed Blocks or Not Bit 16
- 0b_1100 0x_C 12-8 = 4 so 2 to the 4th power = 16 time 256 = 4096 samples. ( 2358 SDC read frame header) frame blocksize
- 0b_0011 0x3 3 sample rate 192,000 ( 2379 SDC read frame header) samplerate'
- 0b1010 & 0b0111 = Case 2 FLAC__CHANNEL_ASSIGNMENT_MID_SIDE Channel Handling
- 0b110 = C 24 bits per sample bps
- 0b_0 Mandatory 0. Validation
32 bits consumed.
| Variable | Decimal | Hex | Location Flac File |
|---|---|---|---|
| Bits | 8 | 8 | |
| br->word | 0xfff8c3ac005e | 1192 | |
| br->consumed_bits | 32 | 0x20 |
Read Frame Header
| Line Number | Code Package | Module | Value | Opertion Description |
|---|---|---|---|---|
| 2319 | SDC | read_frame_header_ | Variables Above | (FLAC__StreamDecoder *decoder) read in the raw header as bytes so we can CRC it, and parse it on the way |
| 420 | BDC | FLAC__bitreader_read_raw_uint32 | 0xC3 0xAC |
(FLAC__BitReader *br, FLAC__uint32 *val, uint32_t bits) |
| 2358 | SDC | read_frame_header_ | 0xC3 | frame.header.blocksize = 256 << (x-8) = 4098 =0x1000 (x = 0xC3 >> 4 = C = 12) |
| 2379 | SDC | read_frame_header_ | 0xC3 | case 3 x &0x0F (x=0xC3) frame.header.sample_rate = 192,000 |
| 2429 | SDC | read_frame_header_ | 0xAC | case 2 frame.header.channel_assignment = FLAC__CHANNEL_ASSIGNMENT_MID_SIDE; |
| 2467 | SDC | read_frame_header_ | 0xAC | case 6 (x = (uint32_t)(raw_header[3] & 0x0e) >> 1) frame.header.bits_per_sample = 32; |
Edit to Here
Read Subframe
| 2082 | SDC | read_frame | NA | Allocate channels +1 bit for channel 1 in MID_SIDE |
| 2093 | SDC | read_frame | channel 0 then 1 bps 24 then 25 |
if(!read_subframe_(decoder, channel, bps, do_full_decode)) |
| 2600 | SDC | read_subframe_ | channel 0 then 1 bps 24 then 25 |
(FLAC__StreamDecoder *decoder, uint32_t channel, uint32_t bps, FLAC__bool do_full_decode) |
| 2606 | SDC | read_subframe_ | x = 78 = 0x4E (return) | FLAC__bitreader_read_raw_uint32(decoder->private_->input, &x, 8) |
| 2625 | SDC | read_subframe_ | channel 0 then 1 bps 24 then 25 |
decoder->private_->frame.subframes[channel].wasted_bits = 0; |
| 2666 | SDC | read_subframe_ | predictor_order = 8 | uint32_t predictor_order = ((x>>1)&31)+1 |
| 2672 | SDC | read_subframe_ | channel 0 then 1 bps 24 then 25 predictor_order = 8 |
if(!read_subframe_lpc_(decoder, channel, bps, predictor_order, do_full_decode)) |
| 2806 | SDC | read_subframe_lpc | channel 0 then 1 bps 24 then 25 order = 8 |
(FLAC__StreamDecoder *decoder, uint32_t channel, uint32_t bps, const uint32_t order, FLAC__bool do_full_decode) |
| 2821 | SDC | read_subframe_lpc | see warmup values below | FLAC__bitreader_read_raw_int64(decoder->private_->input, &i64, bps) |
| Variable | Decimal | Hex | Location Flac File |
|---|---|---|---|
| Bits | 8 | 8 | |
| br->word | 0x4e000000fffff200 | 1192 | |
| br->consumed_bits | 0 | 0x20 |
Edit To Here
References
- ↑ https://www.reddit.com/r/audioengineering/comments/u2t2o4/questions_about_the_way_flac_works_relatively/
- ↑ (see FLAC Agent Build for metadata. Assuming equivalent in pertinent details.