These are common with audio atoms. Without this the demuxer would read two
bytes at a time for a mono 16-bit file.
---
libavformat/mxfdec.c | 43 +++++++++++++++++++++++++++++++++++++++++--
1 files changed, 41 insertions(+), 2 deletions(-)
diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c
index cf9751a..d385a7e 100644
--- a/libavformat/mxfdec.c
+++ b/libavformat/mxfdec.c
@@ -207,6 +207,7 @@ typedef struct {
int current_edit_unit;
int nb_index_tables;
MXFIndexTable *index_tables;
+ int edit_units_per_packet; ///< how many edit units to read at a time
(PCM, OPAtom)
} MXFContext;
enum MXFWrappingScheme {
@@ -1678,6 +1679,38 @@ static inline void
compute_partition_essence_offset(AVFormatContext *s,
}
}
+static int is_pcm(enum CodecID codec_id)
+{
+ /* we only care about "normal" PCM codecs until we get samples */
+ return codec_id >= CODEC_ID_PCM_S16LE && codec_id < CODEC_ID_PCM_S24DAUD;
+}
+
+/**
+ * Deals with the case where for some audio atoms EditUnitByteCount is very
small (2, 4..).
+ * In those cases we should read more than one sample per call to
mxf_read_packet().
+ */
+static void mxf_handle_small_eubc(AVFormatContext *s)
+{
+ MXFContext *mxf = s->priv_data;
+
+ /* assuming non-OPAtom == frame wrapped
+ * no sane writer would wrap 2 byte PCM packets with 20 byte headers.. */
+ if (mxf->op != OPAtom)
+ return;
+
+ /* expect PCM with exactly one index table segment and a small (< 32) EUBC
*/
+ if (s->nb_streams != 1 || s->streams[0]->codec->codec_type !=
AVMEDIA_TYPE_AUDIO ||
+ !is_pcm(s->streams[0]->codec->codec_id) || mxf->nb_index_tables != 1 ||
+ mxf->index_tables[0].nb_segments != 1 ||
+ mxf->index_tables[0].segments[0]->edit_unit_byte_count >= 32)
+ return;
+
+ /* arbitrarily default to 48 kHz PAL audio frame size */
+ /* TODO: we could compute this from the ratio between the audio and video
edit rates
+ * for 48 kHz NTSC we could use the 1802-1802-1802-1802-1801 pattern
*/
+ mxf->edit_units_per_packet = 1920;
+}
+
static int mxf_read_header(AVFormatContext *s, AVFormatParameters *ap)
{
MXFContext *mxf = s->priv_data;
@@ -1686,6 +1719,7 @@ static int mxf_read_header(AVFormatContext *s,
AVFormatParameters *ap)
int ret;
mxf->last_forward_tell = INT64_MAX;
+ mxf->edit_units_per_packet = 1;
if (!mxf_read_sync(s->pb, mxf_header_partition_pack_key, 14)) {
av_log(s, AV_LOG_ERROR, "could not find header partition pack key\n");
@@ -1790,6 +1824,8 @@ static int mxf_read_header(AVFormatContext *s,
AVFormatParameters *ap)
return AVERROR_INVALIDDATA;
}
+ mxf_handle_small_eubc(s);
+
return 0;
}
@@ -1889,6 +1925,7 @@ static int mxf_read_packet(AVFormatContext *s, AVPacket
*pkt)
int64_t ret64, pos, next_pos;
AVStream *st;
MXFIndexTable *t;
+ int edit_units;
if (mxf->op != OPAtom)
return mxf_read_packet_old(s, pkt);
@@ -1901,12 +1938,14 @@ static int mxf_read_packet(AVFormatContext *s, AVPacket
*pkt)
if (mxf->current_edit_unit >= st->duration)
return AVERROR_EOF;
+ edit_units = FFMIN(mxf->edit_units_per_packet, st->duration -
mxf->current_edit_unit);
+
if ((ret = mxf_edit_unit_absolute_offset(mxf, t, mxf->current_edit_unit,
NULL, &pos, 1)) < 0)
return ret;
/* compute size by finding the next edit unit or the end of the essence
container
* not pretty, but it works */
- if ((ret = mxf_edit_unit_absolute_offset(mxf, t, mxf->current_edit_unit +
1, NULL, &next_pos, 0)) < 0 &&
+ if ((ret = mxf_edit_unit_absolute_offset(mxf, t, mxf->current_edit_unit +
edit_units, NULL, &next_pos, 0)) < 0 &&
(next_pos = mxf_essence_container_end(mxf, t->body_sid)) <= 0) {
av_log(s, AV_LOG_ERROR, "unable to compute the size of the last
packet\n");
return AVERROR_INVALIDDATA;
@@ -1930,7 +1969,7 @@ static int mxf_read_packet(AVFormatContext *s, AVPacket
*pkt)
}
pkt->stream_index = 0;
- mxf->current_edit_unit++;
+ mxf->current_edit_unit += edit_units;
return 0;
}
--
1.7.5.4
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