shithub: mp3dec

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take into account bit-reservoir on seek

--- a/minimp3_ex.h

+++ b/minimp3_ex.h

@@ -11,6 +11,8 @@

 #define MP3D_SEEK_TO_BYTE   0

 #define MP3D_SEEK_TO_SAMPLE 1

+#define MINIMP3_PREDECODE_FRAMES 2 /* frames to pre-decode and skip after seek (to fill internal structures) */

+

 #define MP3D_E_MEMORY -1

 typedef struct

@@ -45,17 +47,18 @@

     mp3dec_t mp3d;

     mp3dec_map_info_t file;

     mp3dec_index_t index;

-    uint64_t offset, samples;

+    uint64_t offset, samples, start_offset;

     mp3dec_frame_info_t info;

     mp3d_sample_t buffer[MINIMP3_MAX_SAMPLES_PER_FRAME];

 #ifndef MINIMP3_NO_STDIO

     int is_file;

 #endif

+    int free_format_bytes;

     int seek_method, vbr_tag_found;

     int buffer_samples, buffer_consumed, to_skip;

 } mp3dec_ex_t;

-typedef int (*MP3D_ITERATE_CB)(void *user_data, const uint8_t *frame, int frame_size, size_t offset, mp3dec_frame_info_t *info);

+typedef int (*MP3D_ITERATE_CB)(void *user_data, const uint8_t *frame, int frame_size, int free_format_bytes, size_t offset, mp3dec_frame_info_t *info);

 typedef int (*MP3D_PROGRESS_CB)(void *user_data, size_t file_size, size_t offset, mp3dec_frame_info_t *info);

 #ifdef __cplusplus

@@ -223,7 +226,7 @@

         frames++;

         if (callback)

         {

-            if (callback(user_data, hdr, frame_size, hdr - orig_buf, &frame_info))

+            if (callback(user_data, hdr, frame_size, free_format_bytes, hdr - orig_buf, &frame_info))

                 break;

         }

         buf      += frame_size;

@@ -232,17 +235,19 @@

     return frames;

 }

-static int mp3dec_load_index(void *user_data, const uint8_t *frame, int frame_size, size_t offset, mp3dec_frame_info_t *info)

+static int mp3dec_load_index(void *user_data, const uint8_t *frame, int frame_size, int free_format_bytes, size_t offset, mp3dec_frame_info_t *info)

 {

-    (void)frame_size;

+    static const char g_xing_tag[4] = { 'X', 'i', 'n', 'g' };

+    static const char g_info_tag[4] = { 'I', 'n', 'f', 'o' };

     mp3dec_frame_t *idx_frame;

     mp3dec_ex_t *dec = (mp3dec_ex_t *)user_data;

     if (!dec->index.frames && !dec->vbr_tag_found)

     {   /* detect VBR tag and try to avoid full scan */

+        int i;

         dec->info = *info;

-        static const char g_xing_tag[4] = { 'X', 'i', 'n', 'g' };

-        static const char g_info_tag[4] = { 'I', 'n', 'f', 'o' };

-        for (int i = 5; i < frame_size - 12; i++)

+        dec->start_offset = offset;

+        dec->free_format_bytes = free_format_bytes; /* should not change */

+        for (i = 5; i < frame_size - 12; i++)

         {

             const uint8_t *tag = frame + i;

             if (!memcmp(g_xing_tag, tag, 4) || !memcmp(g_info_tag, tag, 4))

@@ -296,12 +301,13 @@

     if (0 == position)

     {   /* optimize seek to zero, no index needed */

 seek_zero:

-        dec->offset  = 0;

+        dec->offset  = dec->start_offset;

         dec->to_skip = 0;

         goto do_exit;

     }

     if (!dec->index.frames && dec->vbr_tag_found)

     {   /* no index created yet (vbr tag used to calculate track length) */

+        dec->samples = 0;

         if (mp3dec_iterate_buf(dec->file.buffer, dec->file.size, mp3dec_load_index, dec) > 0 && !dec->index.frames)

             return MP3D_E_MEMORY;

     }

@@ -309,11 +315,22 @@

         goto seek_zero; /* no frames in file - seek to zero */

     for (i = 0; i < dec->index.num_frames; i++)

     {

-        if (dec->index.frames[i].sample > position)

+        if (dec->index.frames[i].sample >= position)

             break;

     }

     if (i)

-        i--;

+    {

+        int to_fill_bytes = 511;

+        int skip_frames = MINIMP3_PREDECODE_FRAMES + ((dec->index.frames[i].sample == position) ? 0 : 1);

+        i -= MINIMP3_MIN(i, (size_t)skip_frames);

+        while (i && to_fill_bytes)

+        {   /* make sure bit-reservoir is filled when we start decoding */

+            const uint8_t *hdr = dec->file.buffer + dec->index.frames[i - 1].offset;

+            int frame_size = hdr_frame_bytes(hdr, dec->free_format_bytes) + hdr_padding(hdr);

+            to_fill_bytes -= MINIMP3_MIN(to_fill_bytes, frame_size);

+            i--;

+        }

+    }

     dec->offset = dec->index.frames[i].offset;

     dec->to_skip = position - dec->index.frames[i].sample;

 do_exit:

--- a/minimp3_test.c

+++ b/minimp3_test.c

@@ -67,9 +67,10 @@

     size_t allocated;

 } frames_iterate_data;

-static int frames_iterate_cb(void *user_data, const uint8_t *frame, int frame_size, size_t offset, mp3dec_frame_info_t *info)

+static int frames_iterate_cb(void *user_data, const uint8_t *frame, int frame_size, int free_format_bytes, size_t offset, mp3dec_frame_info_t *info)

 {

     (void)offset;

+    (void)free_format_bytes;

     frames_iterate_data *d = user_data;

     d->info->channels = info->channels;

     d->info->hz       = info->hz;