avformat/iamf_writer: fix coded audio_roll_distance values

'seek_preroll' corresponds to 'audio_roll_distance' in IAMF[1]

[1]https://aomediacodec.github.io/iamf/v1.0.0-errata.html#audio_roll_distance

Signed-off-by: James Almer <jamrial@gmail.com>

libavformat/iamf_parse.c

@@ -683,7 +683,7 @@ static int audio_element_obu(void *s, IAMFContext *c, AVIOContext *pb, int len)
         substream->codecpar->codec_id   = codec_config->codec_id;
         substream->codecpar->frame_size = codec_config->nb_samples;
         substream->codecpar->sample_rate = codec_config->sample_rate;
-        substream->codecpar->seek_preroll = codec_config->seek_preroll;
+        substream->codecpar->seek_preroll = -codec_config->seek_preroll * codec_config->nb_samples;
 
         switch(substream->codecpar->codec_id) {
         case AV_CODEC_ID_AAC:

libavformat/iamf_writer.c

@@ -72,6 +72,34 @@ static int update_extradata(IAMFCodecConfig *codec_config)
     return 0;
 }
 
+static int populate_audio_roll_distance(IAMFCodecConfig *codec_config)
+{
+    switch (codec_config->codec_id) {
+    case AV_CODEC_ID_OPUS:
+        if (!codec_config->nb_samples)
+            return AVERROR(EINVAL);
+        // ceil(3840 / nb_samples)
+        codec_config->seek_preroll = -(1 + ((3840 - 1) / codec_config->nb_samples));
+        break;
+    case AV_CODEC_ID_AAC:
+        codec_config->seek_preroll = -1;
+        break;
+    case AV_CODEC_ID_FLAC:
+    case AV_CODEC_ID_PCM_S16BE:
+    case AV_CODEC_ID_PCM_S24BE:
+    case AV_CODEC_ID_PCM_S32BE:
+    case AV_CODEC_ID_PCM_S16LE:
+    case AV_CODEC_ID_PCM_S24LE:
+    case AV_CODEC_ID_PCM_S32LE:
+        codec_config->seek_preroll = 0;
+        break;
+    default:
+        return AVERROR(EINVAL);
+    }
+
+    return 0;
+}
+
 static int fill_codec_config(IAMFContext *iamf, const AVStreamGroup *stg,
                              IAMFCodecConfig *codec_config)
 {
@@ -83,7 +111,7 @@ static int fill_codec_config(IAMFContext *iamf, const AVStreamGroup *stg,
     codec_config->sample_rate = st->codecpar->sample_rate;
     codec_config->codec_tag = st->codecpar->codec_tag;
     codec_config->nb_samples = st->codecpar->frame_size;
-    codec_config->seek_preroll = st->codecpar->seek_preroll;
+    populate_audio_roll_distance(codec_config);
     if (st->codecpar->extradata_size) {
         codec_config->extradata = av_memdup(st->codecpar->extradata, st->codecpar->extradata_size);
         if (!codec_config->extradata)