[FFmpeg-devel] [PATCH 3/6] avformat/s337m: New ff_s337m_probe()

From: Nicolas Gaullier <nicolas.gaullier@cji.paris>
To: ffmpeg-devel@ffmpeg.org
Cc: Nicolas Gaullier <nicolas.gaullier@cji.paris>
Subject: [FFmpeg-devel] [PATCH 3/6] avformat/s337m: New ff_s337m_probe()
Date: Mon, 13 Feb 2023 19:09:33 +0100
Message-ID: <20230213180936.815-4-nicolas.gaullier@cji.paris> (raw)
In-Reply-To: <20230213180936.815-1-nicolas.gaullier@cji.paris>

Similar to ff_spdif_probe() with just an additional checking of
the bit resolution of the container as it may be 16 or 24 for s337m.
---
 libavformat/s337m.c | 32 ++++++++++++++++++++++++++++++++
 libavformat/s337m.h | 16 ++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/libavformat/s337m.c b/libavformat/s337m.c
index 2a566e3cba..9d2ac265b6 100644
--- a/libavformat/s337m.c
+++ b/libavformat/s337m.c
@@ -135,6 +135,38 @@ static int s337m_probe(const AVProbeData *p)
     return 0;
 }
 
+int ff_s337m_probe(const uint8_t *buf, int size, enum AVCodecID *codec, int container_word_bits)
+{
+    int pos = 0;
+    int consecutive_codes = 0;
+
+    if ( size < S337M_MIN_OFFSET)
+        return 0;
+    size = FFMIN(3 * S337M_MAX_OFFSET, size);
+    if (container_word_bits != 16 && container_word_bits != 24)
+        return AVERROR_INVALIDDATA;
+
+    do {
+        uint64_t state;
+        int data_type, data_size, offset;
+        while (pos < size - 12 && !buf[pos]) {
+            pos++;
+        }
+        if (pos >= size - 12 || pos < S337M_PROBE_GUARDBAND_MIN_BYTES || pos % (container_word_bits == 16 ? 4 : 6))
+            return 0;
+        state = container_word_bits == 16 ? AV_RB32(buf + pos) : AV_RB48(buf + pos);
+        if (!IS_LE_MARKER(state))
+            return 0;
+        data_type = container_word_bits == 16 ? AV_RL16(buf + pos + 4) : AV_RL24(buf + pos + 6);
+        data_size = container_word_bits == 16 ? AV_RL16(buf + pos + 6) : AV_RL24(buf + pos + 9);
+        if (s337m_get_offset_and_codec(NULL, state, data_type, data_size, container_word_bits, &offset, codec))
+            return 0;
+        pos = ++consecutive_codes * (offset + 4*(container_word_bits == 16 ? 4 : 6));
+    } while (consecutive_codes < 3);
+
+    return AVPROBE_SCORE_MAX;
+}
+
 static int s337m_read_header(AVFormatContext *s)
 {
     s->ctx_flags |= AVFMTCTX_NOHEADER;
diff --git a/libavformat/s337m.h b/libavformat/s337m.h
index af2c4c85a3..94e79dce5d 100644
--- a/libavformat/s337m.h
+++ b/libavformat/s337m.h
@@ -21,6 +21,22 @@
 #ifndef AVFORMAT_S337M_H
 #define AVFORMAT_S337M_H
 
+#define S337M_MIN_OFFSET 1601*4
+#define S337M_MAX_OFFSET 2002*6
+
+#define S337M_PROBE_GUARDBAND_MIN_BYTES     0
+
+/**
+ * Detect s337m packets in a PCM_S16LE/S24LE stereo stream
+ * Requires 3 samples with enough (S337M_PROBE_GUARDBAND_MIN_BYTES) and clean (set to zero) guard band
+ * @param p_buf Buffer
+ * @param size Buffer size
+ * @param codec Returns AV_CODEC_ID_DOLBY_E upon successful probing
+ * @param container_word_bits 16 or 24
+ * @return = AVPROBE_SCORE
+ */
+int ff_s337m_probe(const uint8_t *p_buf, int size, enum AVCodecID *codec, int container_word_bits);
+
 /**
  * Read s337m packets in a PCM_S16LE/S24LE stereo stream
  * Returns the first inner packet found
-- 
2.30.2

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