From 57409f52d5da3665a91c6cf2cbcef86ea1004ccf Mon Sep 17 00:00:00 2001
From: "roman.artiukhin" <bahusdrive@gmail.com>
Date: Tue, 5 Sep 2023 00:45:32 +0300
Subject: Codecs: mp4: Accurate seek in large files with small lookup_table

Read sample_byte_sizes table on demand when it can't be cached

Change-Id: I2191be63ceebfd8b16e1e973e13c5b51986b6564
---
 lib/rbcodec/codecs/libm4a/demux.c | 11 ++++++++++-
 lib/rbcodec/codecs/libm4a/m4a.c   | 19 ++++++++++++++-----
 lib/rbcodec/codecs/libm4a/m4a.h   |  1 +
 3 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/lib/rbcodec/codecs/libm4a/demux.c b/lib/rbcodec/codecs/libm4a/demux.c
index 25462db030..8a424c5187 100644
--- a/lib/rbcodec/codecs/libm4a/demux.c
+++ b/lib/rbcodec/codecs/libm4a/demux.c
@@ -400,7 +400,8 @@ static bool read_chunk_stsz(qtmovie_t *qtmovie, size_t chunk_len)
     }
     else
     {
-        DEBUGF("stsz too large, ignoring it\n");
+        qtmovie->res->sample_byte_sizes_offset = stream_tell(qtmovie->stream);
+        DEBUGF("stsz too large: %u, save sample_byte_sizes_offset\n", numsizes);
     }
 
     if (size_remaining)
@@ -481,6 +482,14 @@ static bool read_chunk_stco(qtmovie_t *qtmovie, size_t chunk_len)
         return false;
     }
 
+    // Reading sample_byte_sizes data on seek can lead to additional re-buffering.
+    // So skip it if we have good enough seek accuracy via lookup_table (3000 ms)
+    if (qtmovie->res->sample_byte_sizes_offset && ci->id3->length / fit_numentries <= 3000)
+    {
+        qtmovie->res->sample_byte_sizes_offset = 0;
+        DEBUGF("lookup_table seek accuracy %ld ms, ignoring sample_byte_sizes_offset \n", ci->id3->length / fit_numentries);
+    }
+
     /* Build up lookup table. The lookup table contains the sample index and
      * byte position in the file for each chunk. This table is used to seek
      * and resume (see m4a_seek() and m4a_seek_raw() in libm4a/m4a.c) and 
diff --git a/lib/rbcodec/codecs/libm4a/m4a.c b/lib/rbcodec/codecs/libm4a/m4a.c
index 295c39c5ff..b63b8bad2c 100644
--- a/lib/rbcodec/codecs/libm4a/m4a.c
+++ b/lib/rbcodec/codecs/libm4a/m4a.c
@@ -211,11 +211,13 @@ unsigned int m4a_seek(demux_res_t* demux_res, stream_t* stream,
         sound_sample_i += time_cnt * time_dur;
     }
 
-    DEBUGF("seek chunk=%lu, sample=%lu, soundsample=%lu, offset=%lu\n",
-           (unsigned long)chunk, (unsigned long)chunk_first_sample,
-           sound_sample_i, (unsigned long)offset);
+    if (demux_res->sample_byte_sizes_offset)
+    {
+        stream->ci->seek_buffer(demux_res->sample_byte_sizes_offset + chunk_first_sample * 4);
+    }
 
-    if (tsz_tab) {
+    if (tsz_tab || demux_res->sample_byte_sizes_offset)
+    {
         /* We have a sample-to-bytes table available so we can do accurate
          * seeking. Move one sample at a time and update the file offset and
          * PCM sample offset as we go. */
@@ -229,7 +231,7 @@ unsigned int m4a_seek(demux_res_t* demux_res, stream_t* stream,
                 time_dur = tts_tab[time].sample_duration;
             }
 
-            offset += tsz_tab[i];
+            offset += tsz_tab ? tsz_tab[i] : stream_read_uint32(stream);
             sound_sample_i += time_dur;
             time_cnt--;
         }
@@ -239,6 +241,13 @@ unsigned int m4a_seek(demux_res_t* demux_res, stream_t* stream,
         sample_i = chunk_first_sample;
     }
 
+    DEBUGF("seek chunk=%lu, chunk_first_sample=%lu, sample_i=%u, soundsample=%lu, offset=%lu\n",
+           (unsigned long)chunk,
+           (unsigned long)chunk_first_sample,
+           sample_i,
+           (unsigned long)sound_sample_i,
+           (unsigned long)offset);
+
     if (stream->ci->seek_buffer(offset))
     {
         *sound_samples_done = sound_sample_i;
diff --git a/lib/rbcodec/codecs/libm4a/m4a.h b/lib/rbcodec/codecs/libm4a/m4a.h
index 7120f8b4c6..14b22f5dbf 100644
--- a/lib/rbcodec/codecs/libm4a/m4a.h
+++ b/lib/rbcodec/codecs/libm4a/m4a.h
@@ -82,6 +82,7 @@ typedef struct
 
     uint32_t *sample_byte_sizes;
     uint32_t num_sample_byte_sizes;
+    int32_t sample_byte_sizes_offset;
 
     uint32_t codecdata_len;
     uint8_t codecdata[MAX_CODECDATA_SIZE];
-- 
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