PR #20243 opened by Manuel Lauss (mlauss2) URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20243 Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20243.patch
Add support to the LucasArts VIMA decoder for the IMA4 variant. This is a fix for Trac Ticket #5406 (https://trac.ffmpeg.org/ticket/5406) RFC because: the implementation I made here works for the first chunk, but all subsequent chunks have popping noises in them. Maybe it's too hot here at the moment, but I cannot find the reason why, especially since I've derived this from an already flawlessly working implementation I made earlier. Am I missing something in ffmpeg? 2 sample files are at https://samples.ffmpeg.org/ffmpeg-bugs/trac/ticket5406/ Thanks! >From 62f3796e78cfde3ef0d1505b97e1b4528f8f2943 Mon Sep 17 00:00:00 2001 From: Manuel Lauss <manuel.la...@gmail.com> Date: Fri, 15 Aug 2025 11:40:55 +0200 Subject: [PATCH] avcodec/vima: add IMA4 support ADPCM based on 4-bit input nibbles. --- libavcodec/vima.c | 100 ++++++++++++++++++++++++++++++---------------- 1 file changed, 66 insertions(+), 34 deletions(-) diff --git a/libavcodec/vima.c b/libavcodec/vima.c index 56cc1b7a85..63b5690a89 100644 --- a/libavcodec/vima.c +++ b/libavcodec/vima.c @@ -85,6 +85,10 @@ static const int8_t *const step_index_tables[] = { index_table4, index_table5, index_table6 }; +static const int8_t ima4_table[] = { + -1, -1, -1, -1, 2, 4, 6, 8, -1, -1, -1, -1, 2, 4, 6, 8 +}; + static av_cold void predict_table_init(void) { for (int start_pos = 0; start_pos < 64; start_pos++) { @@ -159,49 +163,77 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *frame, if ((ret = ff_get_buffer(avctx, frame, 0)) < 0) return ret; - for (chan = 0; chan < channels; chan++) { - uint16_t *dest = (uint16_t *)frame->data[0] + chan; - int step_index = channel_hint[chan]; - int output = pcm_data[chan]; - int sample; + if (show_bits_long(&gb, 32) == MKBETAG('I','M','A','4')) { + int16_t *dest = (int16_t *)frame->data[0]; + int dat, nib, adpcm_step, diff, step_index; - for (sample = 0; sample < samples; sample++) { - int lookup_size, lookup, highbit, lowbits; + adpcm_step = 7; + skip_bits_long(&gb, 32); /* skip the 'IMA4' tag */ + dat = (int16_t)get_sbits(&gb, 16); + step_index = get_bits(&gb, 8); + for (int i = 0; i < samples; i++) { + nib = get_bits(&gb, 4); + diff = adpcm_step >> 3; + if (nib & 4) + diff += adpcm_step; + if (nib & 2) + diff += (adpcm_step >> 1); + if (nib & 1) + diff += (adpcm_step >> 2); + if (nib & 8) + diff = -diff; + dat = av_clip_int16(dat + diff); + for (int j = 0; j < channels; j++) + *dest++ = dat; - step_index = av_clip(step_index, 0, 88); - lookup_size = size_table[step_index]; - lookup = get_bits(&gb, lookup_size); - highbit = 1 << (lookup_size - 1); - lowbits = highbit - 1; + step_index = av_clip(step_index + ima4_table[nib], 0, 88); + if (step_index > 0) + adpcm_step = ff_adpcm_step_table[step_index]; + } + } else { + for (chan = 0; chan < channels; chan++) { + uint16_t *dest = (uint16_t *)frame->data[0] + chan; + int step_index = channel_hint[chan]; + int output = pcm_data[chan]; + int sample; - if (lookup & highbit) - lookup ^= highbit; - else - highbit = 0; + for (sample = 0; sample < samples; sample++) { + int lookup_size, lookup, highbit, lowbits; - if (lookup == lowbits) { - output = get_sbits(&gb, 16); - } else { - int predict_index, diff; + step_index = av_clip(step_index, 0, 88); + lookup_size = size_table[step_index]; + lookup = get_bits(&gb, lookup_size); + highbit = 1 << (lookup_size - 1); + lowbits = highbit - 1; - predict_index = (lookup << (7 - lookup_size)) | (step_index << 6); - predict_index = av_clip(predict_index, 0, 5785); - diff = predict_table[predict_index]; - if (lookup) - diff += ff_adpcm_step_table[step_index] >> (lookup_size - 1); - if (highbit) - diff = -diff; + if (lookup & highbit) + lookup ^= highbit; + else + highbit = 0; - output = av_clip_int16(output + diff); + if (lookup == lowbits) { + output = get_sbits(&gb, 16); + } else { + int predict_index, diff; + + predict_index = (lookup << (7 - lookup_size)) | (step_index << 6); + predict_index = av_clip(predict_index, 0, 5785); + diff = predict_table[predict_index]; + if (lookup) + diff += ff_adpcm_step_table[step_index] >> (lookup_size - 1); + if (highbit) + diff = -diff; + + output = av_clip_int16(output + diff); + } + + *dest = output; + dest += channels; + + step_index += step_index_tables[lookup_size - 2][lookup]; } - - *dest = output; - dest += channels; - - step_index += step_index_tables[lookup_size - 2][lookup]; } } - *got_frame_ptr = 1; return pkt->size; -- 2.49.1 _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
