[FFmpeg-devel] [PATCH] lavf/matroska: expose stream encoding as global side-data

[Rodger Combs]

Some demuxers can't handle Matroska compression, so this lets API users
check if a file uses it and determine whether those players will fail.
---
 libavcodec/avcodec.h      | 35 ++++++++++++++++++++++++++++++++++-
 libavcodec/avpacket.c     |  1 +
 libavcodec/version.h      |  2 +-
 libavformat/matroskadec.c | 23 +++++++++++++++++------
 4 files changed, 53 insertions(+), 8 deletions(-)

diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index 7a56899..bd42f58 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -1227,6 +1227,34 @@ typedef struct AVCPBProperties {
     uint64_t vbv_delay;
 } AVCPBProperties;
 
+/**
+ * This structure describes the Matroska encoding (compression or encryption) applied to
+ * a stream. It can be useful when determining whether or not other demuxers can handle
+ * a file, since some players don't support header compression.
+ */
+typedef struct AVMatroskaEncoding {
+    /**
+     * Type of content encoding. 0 for compression; 1 for encryption.
+     */
+    uint64_t type;
+    /**
+     * Algorithm used for the compression or encryption.
+     * For compression:
+     * 0 - zlib,
+     * 1 - bzlib,
+     * 2 - lzo1x
+     * 3 - Header Stripping
+     * For encryption:
+     * 0 - Signing only
+     * 1 - DES
+     * 2 - 3DES
+     * 3 - Twofish
+     * 4 - Blowfish
+     * 5 - AES
+     */
+    uint64_t algorithm;
+} AVMatroskaEncoding;
+
 #if FF_API_QSCALE_TYPE
 #define FF_QSCALE_TYPE_MPEG1 0
 #define FF_QSCALE_TYPE_MPEG2 1
@@ -1414,7 +1442,12 @@ enum AVPacketSideDataType {
      * should be associated with a video stream and containts data in the form
      * of the AVMasteringDisplayMetadata struct.
      */
-    AV_PKT_DATA_MASTERING_DISPLAY_METADATA
+    AV_PKT_DATA_MASTERING_DISPLAY_METADATA,
+
+    /**
+     * Corresponds to the AVMatroskaEncoding struct.
+     */
+    AV_PKT_DATA_MATROSKA_ENCODING,
 };
 
 #define AV_PKT_DATA_QUALITY_FACTOR AV_PKT_DATA_QUALITY_STATS //DEPRECATED
diff --git a/libavcodec/avpacket.c b/libavcodec/avpacket.c
index 97f079f..6a9811b 100644
--- a/libavcodec/avpacket.c
+++ b/libavcodec/avpacket.c
@@ -353,6 +353,7 @@ const char *av_packet_side_data_name(enum AVPacketSideDataType type)
     case AV_PKT_DATA_METADATA_UPDATE:            return "Metadata Update";
     case AV_PKT_DATA_MPEGTS_STREAM_ID:           return "MPEGTS Stream ID";
     case AV_PKT_DATA_MASTERING_DISPLAY_METADATA: return "Mastering display metadata";
+    case AV_PKT_DATA_MATROSKA_ENCODING:          return "Matroska Encoding";
     }
     return NULL;
 }
diff --git a/libavcodec/version.h b/libavcodec/version.h
index 0856b19..c937eaf 100644
--- a/libavcodec/version.h
+++ b/libavcodec/version.h
@@ -29,7 +29,7 @@
 
 #define LIBAVCODEC_VERSION_MAJOR  57
 #define LIBAVCODEC_VERSION_MINOR  25
-#define LIBAVCODEC_VERSION_MICRO 101
+#define LIBAVCODEC_VERSION_MICRO 102
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
                                                LIBAVCODEC_VERSION_MINOR, \
diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index d788232..d2172ac 100644
--- a/libavformat/matroskadec.c
+++ b/libavformat/matroskadec.c
@@ -1769,6 +1769,10 @@ static int matroska_parse_tracks(AVFormatContext *s)
         if (!track->codec_id)
             continue;
 
+        st = track->stream = avformat_new_stream(s, NULL);
+        if (!st)
+            return AVERROR(ENOMEM);
+
         if (track->audio.samplerate < 0 || track->audio.samplerate > INT_MAX ||
             isnan(track->audio.samplerate)) {
             av_log(matroska->ctx, AV_LOG_WARNING,
@@ -1794,7 +1798,16 @@ static int matroska_parse_tracks(AVFormatContext *s)
             av_log(matroska->ctx, AV_LOG_ERROR,
                    "Multiple combined encodings not supported");
         } else if (encodings_list->nb_elem == 1) {
+            AVMatroskaEncoding *side_data = (void*)av_stream_new_side_data(st,
+                                                     AV_PKT_DATA_MATROSKA_ENCODING,
+                                                     sizeof(AVMatroskaEncoding));
+            if (!side_data)
+                return AVERROR(ENOMEM);
+
+            side_data->type = encodings[0].type;
+
             if (encodings[0].type) {
+                side_data->algorithm = encodings[0].encryption.algo;
                 if (encodings[0].encryption.key_id.size > 0) {
                     /* Save the encryption key id to be stored later as a
                        metadata tag. */
@@ -1822,10 +1835,12 @@ static int matroska_parse_tracks(AVFormatContext *s)
                  encodings[0].compression.algo != MATROSKA_TRACK_ENCODING_COMP_LZO   &&
 #endif
                  encodings[0].compression.algo != MATROSKA_TRACK_ENCODING_COMP_HEADERSTRIP) {
+                side_data->algorithm = encodings[0].compression.algo;
                 encodings[0].scope = 0;
                 av_log(matroska->ctx, AV_LOG_ERROR,
                        "Unsupported encoding type");
             } else if (track->codec_priv.size && encodings[0].scope & 2) {
+                side_data->algorithm = encodings[0].compression.algo;
                 uint8_t *codec_priv = track->codec_priv.data;
                 int ret = matroska_decode_buffer(&track->codec_priv.data,
                                                  &track->codec_priv.size,
@@ -1839,6 +1854,8 @@ static int matroska_parse_tracks(AVFormatContext *s)
 
                 if (codec_priv != track->codec_priv.data)
                     av_free(codec_priv);
+            } else {
+                side_data->algorithm = encodings[0].compression.algo;
             }
         }
 
@@ -1850,12 +1867,6 @@ static int matroska_parse_tracks(AVFormatContext *s)
             }
         }
 
-        st = track->stream = avformat_new_stream(s, NULL);
-        if (!st) {
-            av_free(key_id_base64);
-            return AVERROR(ENOMEM);
-        }
-
         if (key_id_base64) {
             /* export encryption key id as base64 metadata tag */
             av_dict_set(&st->metadata, "enc_key_id", key_id_base64, 0);
-- 
2.7.2