From: Manuel Lauss via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>
To: ffmpeg-devel@ffmpeg.org
Cc: Manuel Lauss <code@ffmpeg.org>
Subject: [FFmpeg-devel] [PATCH] avcodec/vima: support IMA4 (ADPCM QT) variant (PR #20253)
Date: Sat, 16 Aug 2025 11:59:38 +0300 (EEST)
Message-ID: <20250816085938.A197E68D384@ffbox0-bg.ffmpeg.org> (raw)
PR #20253 opened by Manuel Lauss (mlauss2)
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20253
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20253.patch
Some versions of LucasArts SANM Audio chunks have a special "IMA4" tag in their VIMA chunks, to indicate that
a different coding scheme, in this case IMA ADPCM QT, is used.
- adpcm: export the ff_adpcm_ima_qt_expand_nibble() function
- vima: recognize the IMA4 tag
From c90ac9a8f94cbae9085c0a429f0e8ac95b687a25 Mon Sep 17 00:00:00 2001
From: Manuel Lauss <manuel.lauss@gmail.com>
Date: Sat, 16 Aug 2025 10:24:34 +0200
Subject: [PATCH 1/2] avcodec/adpcm: export ff_adpcm_ima_qt_expand_nibble
For use in the LucasArts VIMA decoder, where it is used as a subvariant.
---
libavcodec/adpcm.c | 18 +++++++++---------
libavcodec/adpcm.h | 1 +
2 files changed, 10 insertions(+), 9 deletions(-)
diff --git a/libavcodec/adpcm.c b/libavcodec/adpcm.c
index 83ef7c780a..4c15be6207 100644
--- a/libavcodec/adpcm.c
+++ b/libavcodec/adpcm.c
@@ -518,7 +518,7 @@ static inline int16_t adpcm_ima_wav_expand_nibble(ADPCMChannelStatus *c, GetBitC
return (int16_t)c->predictor;
}
-static inline int adpcm_ima_qt_expand_nibble(ADPCMChannelStatus *c, int nibble)
+int16_t ff_adpcm_ima_qt_expand_nibble(ADPCMChannelStatus *c, int nibble)
{
int step_index;
int predictor;
@@ -1335,8 +1335,8 @@ static int adpcm_decode_frame(AVCodecContext *avctx, AVFrame *frame,
for (int m = 0; m < 64; m += 2) {
int byte = bytestream2_get_byteu(&gb);
- samples[m ] = adpcm_ima_qt_expand_nibble(cs, byte & 0x0F);
- samples[m + 1] = adpcm_ima_qt_expand_nibble(cs, byte >> 4 );
+ samples[m ] = ff_adpcm_ima_qt_expand_nibble(cs, byte & 0x0F);
+ samples[m + 1] = ff_adpcm_ima_qt_expand_nibble(cs, byte >> 4 );
}
}
) /* End of CASE */
@@ -1689,16 +1689,16 @@ static int adpcm_decode_frame(AVCodecContext *avctx, AVFrame *frame,
CASE(ADPCM_IMA_SSI,
for (int n = nb_samples >> (1 - st); n > 0; n--) {
int v = bytestream2_get_byteu(&gb);
- *samples++ = adpcm_ima_qt_expand_nibble(&c->status[0], v >> 4 );
- *samples++ = adpcm_ima_qt_expand_nibble(&c->status[st], v & 0x0F);
+ *samples++ = ff_adpcm_ima_qt_expand_nibble(&c->status[0], v >> 4 );
+ *samples++ = ff_adpcm_ima_qt_expand_nibble(&c->status[st], v & 0x0F);
}
) /* End of CASE */
CASE(ADPCM_IMA_APM,
for (int n = nb_samples / 2; n > 0; n--) {
for (int channel = 0; channel < channels; channel++) {
int v = bytestream2_get_byteu(&gb);
- *samples++ = adpcm_ima_qt_expand_nibble(&c->status[channel], v >> 4 );
- samples[st] = adpcm_ima_qt_expand_nibble(&c->status[channel], v & 0x0F);
+ *samples++ = ff_adpcm_ima_qt_expand_nibble(&c->status[channel], v >> 4 );
+ samples[st] = ff_adpcm_ima_qt_expand_nibble(&c->status[channel], v & 0x0F);
}
samples += channels;
}
@@ -2154,8 +2154,8 @@ static int adpcm_decode_frame(AVCodecContext *avctx, AVFrame *frame,
for (int n = nb_samples >> (1 - st); n > 0; n--) {
int v = bytestream2_get_byteu(&gb);
- *samples++ = adpcm_ima_qt_expand_nibble(&c->status[0 ], v >> 4 );
- *samples++ = adpcm_ima_qt_expand_nibble(&c->status[st], v & 0xf);
+ *samples++ = ff_adpcm_ima_qt_expand_nibble(&c->status[0 ], v >> 4 );
+ *samples++ = ff_adpcm_ima_qt_expand_nibble(&c->status[st], v & 0xf);
}
) /* End of CASE */
CASE(ADPCM_CT,
diff --git a/libavcodec/adpcm.h b/libavcodec/adpcm.h
index 0ffc3da1d0..ff70e62078 100644
--- a/libavcodec/adpcm.h
+++ b/libavcodec/adpcm.h
@@ -44,5 +44,6 @@ typedef struct ADPCMChannelStatus {
} ADPCMChannelStatus;
int16_t ff_adpcm_argo_expand_nibble(ADPCMChannelStatus *cs, int nibble, int shift, int flag);
+int16_t ff_adpcm_ima_qt_expand_nibble(ADPCMChannelStatus *c, int nibble);
#endif /* AVCODEC_ADPCM_H */
--
2.49.1
From f0c79aec9d07be81a71e2c18c4be9d3f98478411 Mon Sep 17 00:00:00 2001
From: Manuel Lauss <manuel.lauss@gmail.com>
Date: Sat, 16 Aug 2025 10:44:06 +0200
Subject: [PATCH 2/2] avcodec/vima: IMA4 subtag support
Support decoding of the IMA4 ADPCM QT scheme used in some LucasArts
SANM files.
---
libavcodec/vima.c | 81 ++++++++++++++++++++++++++++-------------------
1 file changed, 48 insertions(+), 33 deletions(-)
diff --git a/libavcodec/vima.c b/libavcodec/vima.c
index 56cc1b7a85..bde7033c2c 100644
--- a/libavcodec/vima.c
+++ b/libavcodec/vima.c
@@ -28,6 +28,7 @@
#include "libavutil/channel_layout.h"
#include "libavutil/thread.h"
+#include "adpcm.h"
#include "adpcm_data.h"
#include "avcodec.h"
#include "codec_internal.h"
@@ -159,46 +160,60 @@ 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];
+ ADPCMChannelStatus cs;
- for (sample = 0; sample < samples; sample++) {
- int lookup_size, lookup, highbit, lowbits;
+ skip_bits_long(&gb, 32); /* skip the 'IMA4' tag */
+ cs.predictor = (int16_t)get_xbits_le(&gb, 16);
+ cs.step_index = av_clip(get_bits(&gb, 8), 0, 88);
+ for (int i = 0; i < samples; i++) {
+ ff_adpcm_ima_qt_expand_nibble(&cs, get_bits(&gb, 4));
+ for (int j = 0; j < channels; j++)
+ *dest++ = cs.predictor;
+ }
+ } 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;
- 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;
+ for (sample = 0; sample < samples; sample++) {
+ int lookup_size, lookup, highbit, lowbits;
- if (lookup & highbit)
- lookup ^= highbit;
- else
- highbit = 0;
+ 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;
- if (lookup == lowbits) {
- output = get_sbits(&gb, 16);
- } else {
- int predict_index, diff;
+ if (lookup & highbit)
+ lookup ^= highbit;
+ else
+ highbit = 0;
- 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 == lowbits) {
+ output = get_sbits(&gb, 16);
+ } else {
+ int predict_index, diff;
- output = av_clip_int16(output + 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];
}
}
--
2.49.1
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