latmdec: fix audio specific config parsing

Pass the correct size in bits to mpeg4audio_get_config and add a flag
to disable parsing of the sync extension when the size is not known.

Latm with AudioMuxVersion 0 does not specify the size of the audio
specific config. Data after the audio specific config can be
misinterpreted as sync extension resulting in random and wrong configs.

libavcodec/aacdec.c

@@ -452,15 +452,17 @@ static int decode_ga_specific_config(AACContext *ac, AVCodecContext *avctx,
  * @param   ac          pointer to AACContext, may be null
  * @param   avctx       pointer to AVCCodecContext, used for logging
  * @param   m4ac        pointer to MPEG4AudioConfig, used for parsing
- * @param   data        pointer to AVCodecContext extradata
+ * @param   data        pointer to buffer holding an audio specific config
- * @param   data_size   size of AVCCodecContext extradata
+ * @param   bit_size    size of audio specific config or data in bits
+ * @param   sync_extension look for an appended sync extension
  *
  * @return  Returns error status or number of consumed bits. <0 - error
  */
 static int decode_audio_specific_config(AACContext *ac,
                                         AVCodecContext *avctx,
                                         MPEG4AudioConfig *m4ac,
-                                        const uint8_t *data, int data_size)
+                                        const uint8_t *data, int bit_size,
+                                        int sync_extension)
 {
     GetBitContext gb;
     int i;
@@ -470,9 +472,9 @@ static int decode_audio_specific_config(AACContext *ac,
          av_dlog(avctx, "%02x ", avctx->extradata[i]);
     av_dlog(avctx, "\n");
 
-    init_get_bits(&gb, data, data_size * 8);
+    init_get_bits(&gb, data, bit_size);
 
-    if ((i = avpriv_mpeg4audio_get_config(m4ac, data, data_size)) < 0)
+    if ((i = avpriv_mpeg4audio_get_config(m4ac, data, bit_size, sync_extension)) < 0)
         return -1;
     if (m4ac->sampling_index > 12) {
         av_log(avctx, AV_LOG_ERROR, "invalid sampling rate index %d\n", m4ac->sampling_index);
@@ -572,7 +574,7 @@ static av_cold int aac_decode_init(AVCodecContext *avctx)
     if (avctx->extradata_size > 0) {
         if (decode_audio_specific_config(ac, ac->avctx, &ac->m4ac,
                                          avctx->extradata,
-                                         avctx->extradata_size) < 0)
+                                         avctx->extradata_size*8, 1) < 0)
             return -1;
     } else {
         int sr, i;
@@ -2315,13 +2317,20 @@ static inline uint32_t latm_get_value(GetBitContext *b)
 }
 
 static int latm_decode_audio_specific_config(struct LATMContext *latmctx,
-                                             GetBitContext *gb)
+                                             GetBitContext *gb, int asclen)
 {
     AVCodecContext *avctx = latmctx->aac_ctx.avctx;
     MPEG4AudioConfig m4ac;
     int config_start_bit  = get_bits_count(gb);
+    int sync_extension    = 0;
     int bits_consumed, esize;
 
+    if (asclen) {
+        sync_extension = 1;
+        asclen         = FFMIN(asclen, get_bits_left(gb));
+    } else
+        asclen         = get_bits_left(gb);
+
     if (config_start_bit % 8) {
         av_log_missing_feature(latmctx->aac_ctx.avctx, "audio specific "
                                "config not byte aligned.\n", 1);
@@ -2330,7 +2339,7 @@ static int latm_decode_audio_specific_config(struct LATMContext *latmctx,
         bits_consumed =
             decode_audio_specific_config(NULL, avctx, &m4ac,
                                          gb->buffer + (config_start_bit / 8),
-                                         get_bits_left(gb) / 8);
+                                         asclen, sync_extension);
 
         if (bits_consumed < 0)
             return AVERROR_INVALIDDATA;
@@ -2388,11 +2397,11 @@ static int read_stream_mux_config(struct LATMContext *latmctx,
 
         // for all but first stream: use_same_config = get_bits(gb, 1);
         if (!audio_mux_version) {
-            if ((ret = latm_decode_audio_specific_config(latmctx, gb)) < 0)
+            if ((ret = latm_decode_audio_specific_config(latmctx, gb, 0)) < 0)
                 return ret;
         } else {
             int ascLen = latm_get_value(gb);
-            if ((ret = latm_decode_audio_specific_config(latmctx, gb)) < 0)
+            if ((ret = latm_decode_audio_specific_config(latmctx, gb, ascLen)) < 0)
                 return ret;
             ascLen -= ret;
             skip_bits_long(gb, ascLen);
@@ -2514,7 +2523,7 @@ static int latm_decode_frame(AVCodecContext *avctx, void *out,
         } else {
             if ((err = decode_audio_specific_config(
                     &latmctx->aac_ctx, avctx, &latmctx->aac_ctx.m4ac,
-                    avctx->extradata, avctx->extradata_size)) < 0)
+                    avctx->extradata, avctx->extradata_size*8, 1)) < 0)
                 return err;
             latmctx->initialized = 1;
         }

libavcodec/alsdec.c

@@ -291,7 +291,7 @@ static av_cold int read_specific_config(ALSDecContext *ctx)
     init_get_bits(&gb, avctx->extradata, avctx->extradata_size * 8);
 
     config_offset = avpriv_mpeg4audio_get_config(&m4ac, avctx->extradata,
-                                             avctx->extradata_size);
+                                                 avctx->extradata_size * 8, 1);
 
     if (config_offset < 0)
         return -1;

libavcodec/mpeg4audio.c

@@ -76,12 +76,13 @@ static inline int get_sample_rate(GetBitContext *gb, int *index)
         avpriv_mpeg4audio_sample_rates[*index];
 }
 
-int avpriv_mpeg4audio_get_config(MPEG4AudioConfig *c, const uint8_t *buf, int buf_size)
+int avpriv_mpeg4audio_get_config(MPEG4AudioConfig *c, const uint8_t *buf,
+                                 int bit_size, int sync_extension)
 {
     GetBitContext gb;
     int specific_config_bitindex;
 
-    init_get_bits(&gb, buf, buf_size*8);
+    init_get_bits(&gb, buf, bit_size);
     c->object_type = get_object_type(&gb);
     c->sample_rate = get_sample_rate(&gb, &c->sampling_index);
     c->chan_config = get_bits(&gb, 4);
@@ -117,7 +118,7 @@ int avpriv_mpeg4audio_get_config(MPEG4AudioConfig *c, const uint8_t *buf, int bu
             return -1;
     }
 
-    if (c->ext_object_type != AOT_SBR) {
+    if (c->ext_object_type != AOT_SBR && sync_extension) {
         while (get_bits_left(&gb) > 15) {
             if (show_bits(&gb, 11) == 0x2b7) { // sync extension
                 get_bits(&gb, 11);

libavcodec/mpeg4audio.h

@@ -42,14 +42,17 @@ typedef struct {
 
 extern const int avpriv_mpeg4audio_sample_rates[16];
 extern const uint8_t ff_mpeg4audio_channels[8];
+
 /**
  * Parse MPEG-4 systems extradata to retrieve audio configuration.
  * @param[in] c        MPEG4AudioConfig structure to fill.
  * @param[in] buf      Extradata from container.
- * @param[in] buf_size Extradata size.
+ * @param[in] bit_size Extradata size in bits.
+ * @param[in] sync_extension look for a sync extension after config if true.
  * @return On error -1 is returned, on success AudioSpecificConfig bit index in extradata.
  */
-int avpriv_mpeg4audio_get_config(MPEG4AudioConfig *c, const uint8_t *buf, int buf_size);
+int avpriv_mpeg4audio_get_config(MPEG4AudioConfig *c, const uint8_t *buf,
+                                 int bit_size, int sync_extension);
 
 enum AudioObjectType {
     AOT_NULL,

libavcodec/mpegaudiodec.c

@@ -1966,7 +1966,8 @@ static int decode_init_mp3on4(AVCodecContext * avctx)
         return AVERROR_INVALIDDATA;
     }
 
-    avpriv_mpeg4audio_get_config(&cfg, avctx->extradata, avctx->extradata_size);
+    avpriv_mpeg4audio_get_config(&cfg, avctx->extradata,
+                                 avctx->extradata_size * 8, 1);
     if (!cfg.chan_config || cfg.chan_config > 7) {
         av_log(avctx, AV_LOG_ERROR, "Invalid channel config number.\n");
         return AVERROR_INVALIDDATA;

libavformat/adtsenc.c

@@ -37,7 +37,7 @@ int ff_adts_decode_extradata(AVFormatContext *s, ADTSContext *adts, uint8_t *buf
     int off;
 
     init_get_bits(&gb, buf, size * 8);
-    off = avpriv_mpeg4audio_get_config(&m4ac, buf, size);
+    off = avpriv_mpeg4audio_get_config(&m4ac, buf, size * 8, 1);
     if (off < 0)
         return off;
     skip_bits_long(&gb, off);

libavformat/flvdec.c

@@ -534,7 +534,7 @@ static int flv_read_packet(AVFormatContext *s, AVPacket *pkt)
             if (st->codec->codec_id == CODEC_ID_AAC) {
                 MPEG4AudioConfig cfg;
                 avpriv_mpeg4audio_get_config(&cfg, st->codec->extradata,
-                                         st->codec->extradata_size);
+                                             st->codec->extradata_size * 8, 1);
                 st->codec->channels = cfg.channels;
                 if (cfg.ext_sample_rate)
                     st->codec->sample_rate = cfg.ext_sample_rate;

libavformat/isom.c

@@ -436,7 +436,7 @@ int ff_mp4_read_dec_config_descr(AVFormatContext *fc, AVStream *st, AVIOContext
         if (st->codec->codec_id == CODEC_ID_AAC) {
             MPEG4AudioConfig cfg;
             avpriv_mpeg4audio_get_config(&cfg, st->codec->extradata,
-                                     st->codec->extradata_size);
+                                         st->codec->extradata_size * 8, 1);
             st->codec->channels = cfg.channels;
             if (cfg.object_type == 29 && cfg.sampling_index < 3) // old mp3on4
                 st->codec->sample_rate = avpriv_mpa_freq_tab[cfg.sampling_index];

libavformat/latmenc.c

@@ -54,7 +54,7 @@ static int latm_decode_extradata(LATMContext *ctx, uint8_t *buf, int size)
     MPEG4AudioConfig m4ac;
 
     init_get_bits(&gb, buf, size * 8);
-    ctx->off = avpriv_mpeg4audio_get_config(&m4ac, buf, size);
+    ctx->off = avpriv_mpeg4audio_get_config(&m4ac, buf, size * 8, 1);
     if (ctx->off < 0)
         return ctx->off;
     skip_bits_long(&gb, ctx->off);

libavformat/matroskaenc.c

@@ -448,7 +448,8 @@ static void get_aac_sample_rates(AVFormatContext *s, AVCodecContext *codec, int
 {
     MPEG4AudioConfig mp4ac;
 
-    if (avpriv_mpeg4audio_get_config(&mp4ac, codec->extradata, codec->extradata_size) < 0) {
+    if (avpriv_mpeg4audio_get_config(&mp4ac, codec->extradata,
+                                     codec->extradata_size * 8, 1) < 0) {
         av_log(s, AV_LOG_WARNING, "Error parsing AAC extradata, unable to determine samplerate.\n");
         return;
     }