qtmux: Join chunks together if they have the same size

Previously we were switching from one chunk to another on every single
buffer. This wastes some space in the headers and, depending on the
software, might depend in more reads (e.g. if the software is reading
multiple samples in one go if they're in the same chunk).

https://bugzilla.gnome.org/show_bug.cgi?id=771478

1 files changed, 59 insertions, 10 deletions

diff --git a/gst/isomp4/atoms.c b/gst/isomp4/atoms.c
index 54455439b..f1ec6bcd2 100644
--- a/gst/isomp4/atoms.c
+++ b/gst/isomp4/atoms.c
@@ -2198,12 +2198,20 @@ atom_stsc_copy_data (AtomSTSC * stsc, guint8 ** buffer, guint64 * size,
     guint64 * offset)
 {
   guint64 original_offset = *offset;
-  guint i;
+  guint i, len;
 
   if (!atom_full_copy_data (&stsc->header, buffer, size, offset)) {
     return 0;
   }
 
+  /* Last two entries might be the same size here as we only merge once the
+   * next chunk is started */
+  if ((len = atom_array_get_len (&stsc->entries)) > 1 &&
+      ((atom_array_index (&stsc->entries, len - 1)).samples_per_chunk ==
+          (atom_array_index (&stsc->entries, len - 2)).samples_per_chunk)) {
+    stsc->entries.len--;
+  }
+
   prop_copy_uint32 (atom_array_get_len (&stsc->entries), buffer, size, offset);
   /* minimize realloc */
   prop_copy_ensure_buffer (buffer, size, offset,
@@ -2891,7 +2899,6 @@ atom_wave_copy_data (AtomWAVE * wave, guint8 ** buffer,
 static void
 atom_stsc_add_new_entry (AtomSTSC * stsc, guint32 first_chunk, guint32 nsamples)
 {
-  STSCEntry nentry;
   gint len;
 
   if ((len = atom_array_get_len (&stsc->entries)) &&
@@ -2899,10 +2906,37 @@ atom_stsc_add_new_entry (AtomSTSC * stsc, guint32 first_chunk, guint32 nsamples)
           nsamples))
     return;
 
-  nentry.first_chunk = first_chunk;
-  nentry.samples_per_chunk = nsamples;
-  nentry.sample_description_index = 1;
-  atom_array_append (&stsc->entries, nentry, 128);
+  if ((len = atom_array_get_len (&stsc->entries)) > 1 &&
+      ((atom_array_index (&stsc->entries, len - 1)).samples_per_chunk ==
+          (atom_array_index (&stsc->entries, len - 2)).samples_per_chunk)) {
+    STSCEntry *nentry;
+
+    /* Merge last two entries as they have the same number of samples per chunk */
+    nentry = &atom_array_index (&stsc->entries, len - 1);
+    nentry->first_chunk = first_chunk;
+    nentry->samples_per_chunk = nsamples;
+    nentry->sample_description_index = 1;
+  } else {
+    STSCEntry nentry;
+
+    nentry.first_chunk = first_chunk;
+    nentry.samples_per_chunk = nsamples;
+    nentry.sample_description_index = 1;
+    atom_array_append (&stsc->entries, nentry, 128);
+  }
+}
+
+static void
+atom_stsc_update_entry (AtomSTSC * stsc, guint32 first_chunk, guint32 nsamples)
+{
+  gint len;
+
+  len = atom_array_get_len (&stsc->entries);
+  g_assert (len != 0);
+  g_assert (atom_array_index (&stsc->entries,
+          len - 1).first_chunk == first_chunk);
+
+  atom_array_index (&stsc->entries, len - 1).samples_per_chunk += nsamples;
 }
 
 static void
@@ -2946,12 +2980,22 @@ atom_stco64_get_entry_count (AtomSTCO64 * stco64)
   return atom_array_get_len (&stco64->entries);
 }
 
-static void
+/* returns TRUE if a new entry was added */
+static gboolean
 atom_stco64_add_entry (AtomSTCO64 * stco64, guint64 entry)
 {
+  guint32 len;
+
+  /* Only add a new entry if the chunk offset changed */
+  if ((len = atom_array_get_len (&stco64->entries)) &&
+      ((atom_array_index (&stco64->entries, len - 1)) == entry))
+    return FALSE;
+
   atom_array_append (&stco64->entries, entry, 256);
   if (entry > G_MAXUINT32)
     stco64->header.header.type = FOURCC_co64;
+
+  return TRUE;
 }
 
 void
@@ -3011,9 +3055,14 @@ atom_stbl_add_samples (AtomSTBL * stbl, guint32 nsamples, guint32 delta,
 {
   atom_stts_add_entry (&stbl->stts, nsamples, delta);
   atom_stsz_add_entry (&stbl->stsz, nsamples, size);
-  atom_stco64_add_entry (&stbl->stco64, chunk_offset);
-  atom_stsc_add_new_entry (&stbl->stsc,
-      atom_stco64_get_entry_count (&stbl->stco64), nsamples);
+  if (atom_stco64_add_entry (&stbl->stco64, chunk_offset)) {
+    atom_stsc_add_new_entry (&stbl->stsc,
+        atom_stco64_get_entry_count (&stbl->stco64), nsamples);
+  } else {
+    atom_stsc_update_entry (&stbl->stsc,
+        atom_stco64_get_entry_count (&stbl->stco64), nsamples);
+  }
+
   if (sync)
     atom_stbl_add_stss_entry (stbl);
   /* always store to arrange for consistent content */