[FFmpeg-devel] [PATCH 1/2] lavf/matroska: Add functions for WebM DASH Manifest
Vignesh Venkatasubramanian
vigneshv at google.com
Tue Jul 1 00:44:36 CEST 2014
Add functions and logic to matroskadec for use by the WebM DASH Manifest
XML Muxer. The actual muxer is added in a future patch.
Signed-off-by: Vignesh Venkatasubramanian <vigneshv at google.com>
---
libavformat/matroska.h | 12 ++
libavformat/matroskadec.c | 362 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 374 insertions(+)
diff --git a/libavformat/matroska.h b/libavformat/matroska.h
index 3bb5aee..e01b9de 100644
--- a/libavformat/matroska.h
+++ b/libavformat/matroska.h
@@ -284,4 +284,16 @@ extern const AVMetadataConv ff_mkv_metadata_conv[];
extern const char * const ff_matroska_video_stereo_mode[MATROSKA_VIDEO_STEREO_MODE_COUNT];
extern const char * const ff_matroska_video_stereo_plane[MATROSKA_VIDEO_STEREO_PLANE_COUNT];
+/* AVStream Metadata tag keys for WebM Dash Manifest */
+#define INITIALIZATION_RANGE "webm_dash_manifest_initialization_range"
+#define CUES_START "webm_dash_manifest_cues_start"
+#define CUES_END "webm_dash_manifest_cues_end"
+#define FILENAME "webm_dash_manifest_file_name"
+#define BANDWIDTH "webm_dash_manifest_bandwidth"
+#define DURATION "webm_dash_manifest_duration"
+#define CLUSTER_KEYFRAME "webm_dash_manifest_cluster_keyframe"
+#define CUE_TIMESTAMPS "webm_dash_manifest_cue_timestamps"
+#define TRACK_NUMBER "webm_dash_manifest_track_number"
+#define CODEC_PRIVATE_SIZE "webm_dash_manifest_codec_priv_size"
+
#endif /* AVFORMAT_MATROSKA_H */
diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index 213767c..4e45e26 100644
--- a/libavformat/matroskadec.c
+++ b/libavformat/matroskadec.c
@@ -3068,6 +3068,359 @@ static int matroska_read_close(AVFormatContext *s)
return 0;
}
+typedef struct {
+ int64_t start_time_ns;
+ int64_t end_time_ns;
+ int64_t start_offset;
+ int64_t end_offset;
+} CueDesc;
+
+/* This function searches all the Cues and returns the CueDesc corresponding the
+ * the timestamp ts. Returned CueDesc will be such that start_time_ns <= ts <
+ * end_time_ns. All 4 fields will be set to -1 if ts >= file's duration.
+ */
+static CueDesc get_cue_desc(AVFormatContext *s, int64_t ts, int64_t cues_start) {
+ MatroskaDemuxContext *matroska = s->priv_data;
+ CueDesc cue_desc;
+ int i;
+ int nb_index_entries = s->streams[0]->nb_index_entries;
+ AVIndexEntry *index_entries = s->streams[0]->index_entries;
+ if (ts >= matroska->duration * matroska->time_scale) return (CueDesc) {-1, -1, -1, -1};
+ for (i = 1; i < nb_index_entries; i++) {
+ if (index_entries[i - 1].timestamp * matroska->time_scale <= ts &&
+ index_entries[i].timestamp * matroska->time_scale > ts) {
+ break;
+ }
+ }
+ --i;
+ cue_desc.start_time_ns = index_entries[i].timestamp * matroska->time_scale;
+ cue_desc.start_offset = index_entries[i].pos - matroska->segment_start;
+ if (i != nb_index_entries - 1) {
+ cue_desc.end_time_ns = index_entries[i + 1].timestamp * matroska->time_scale;
+ cue_desc.end_offset = index_entries[i + 1].pos - matroska->segment_start;
+ } else {
+ cue_desc.end_time_ns = matroska->duration * matroska->time_scale;
+ // FIXME: this needs special handling for files where Cues appear
+ // before Clusters. the current logic assumes Cues appear after
+ // Clusters.
+ cue_desc.end_offset = cues_start - matroska->segment_start;
+ }
+ return cue_desc;
+}
+
+static int webm_clusters_start_with_keyframe(AVFormatContext *s)
+{
+ MatroskaDemuxContext *matroska = s->priv_data;
+ int64_t cluster_pos, before_pos;
+ int index, rv = 1;
+ if (s->streams[0]->nb_index_entries <= 0) return 0;
+ // seek to the first cluster using cues.
+ index = av_index_search_timestamp(s->streams[0], 0, 0);
+ if (index < 0) return 0;
+ cluster_pos = s->streams[0]->index_entries[index].pos;
+ before_pos = avio_tell(s->pb);
+ while (1) {
+ int64_t cluster_id = 0, cluster_length = 0;
+ AVPacket *pkt;
+ avio_seek(s->pb, cluster_pos, SEEK_SET);
+ // read cluster id and length
+ ebml_read_num(matroska, matroska->ctx->pb, 4, &cluster_id);
+ ebml_read_length(matroska, matroska->ctx->pb, &cluster_length);
+ if (cluster_id != 0xF43B675) { // done with all clusters
+ break;
+ }
+ avio_seek(s->pb, cluster_pos, SEEK_SET);
+ matroska->current_id = 0;
+ matroska_clear_queue(matroska);
+ if (matroska_parse_cluster(matroska) < 0 ||
+ matroska->num_packets <= 0) {
+ break;
+ }
+ pkt = matroska->packets[0];
+ cluster_pos += cluster_length + 12; // 12 is the offset of the cluster id and length.
+ if (!(pkt->flags & AV_PKT_FLAG_KEY)) {
+ rv = 0;
+ break;
+ }
+ }
+ avio_seek(s->pb, before_pos, SEEK_SET);
+ return rv;
+}
+
+static int buffer_size_after_time_downloaded(int64_t time_ns, double search_sec, int64_t bps,
+ double min_buffer, double* buffer,
+ double* sec_to_download, AVFormatContext *s,
+ int64_t cues_start)
+{
+ double nano_seconds_per_second = 1000000000.0;
+ double time_sec = time_ns / nano_seconds_per_second;
+ int rv = 0;
+ int64_t time_to_search_ns = (int64_t)(search_sec * nano_seconds_per_second);
+ int64_t end_time_ns = time_ns + time_to_search_ns;
+ double sec_downloaded = 0.0;
+ CueDesc desc_curr = get_cue_desc(s, time_ns, cues_start);
+ if (desc_curr.start_time_ns == -1)
+ return -1;
+ *sec_to_download = 0.0;
+
+ // Check for non cue start time.
+ if (time_ns > desc_curr.start_time_ns) {
+ int64_t cue_nano = desc_curr.end_time_ns - time_ns;
+ double percent = (double)(cue_nano) / (desc_curr.end_time_ns - desc_curr.start_time_ns);
+ double cueBytes = (desc_curr.end_offset - desc_curr.start_offset) * percent;
+ double timeToDownload = (cueBytes * 8.0) / bps;
+
+ sec_downloaded += (cue_nano / nano_seconds_per_second) - timeToDownload;
+ *sec_to_download += timeToDownload;
+
+ // Check if the search ends within the first cue.
+ if (desc_curr.end_time_ns >= end_time_ns) {
+ double desc_end_time_sec = desc_curr.end_time_ns / nano_seconds_per_second;
+ double percent_to_sub = search_sec / (desc_end_time_sec - time_sec);
+ sec_downloaded = percent_to_sub * sec_downloaded;
+ *sec_to_download = percent_to_sub * *sec_to_download;
+ }
+
+ if ((sec_downloaded + *buffer) <= min_buffer) {
+ return 1;
+ }
+
+ // Get the next Cue.
+ desc_curr = get_cue_desc(s, desc_curr.end_time_ns, cues_start);
+ }
+
+ while (desc_curr.start_time_ns != -1) {
+ int64_t desc_bytes = desc_curr.end_offset - desc_curr.start_offset;
+ int64_t desc_ns = desc_curr.end_time_ns - desc_curr.start_time_ns;
+ double desc_sec = desc_ns / nano_seconds_per_second;
+ double bits = (desc_bytes * 8.0);
+ double time_to_download = bits / bps;
+
+ sec_downloaded += desc_sec - time_to_download;
+ *sec_to_download += time_to_download;
+
+ if (desc_curr.end_time_ns >= end_time_ns) {
+ double desc_end_time_sec = desc_curr.end_time_ns / nano_seconds_per_second;
+ double percent_to_sub = search_sec / (desc_end_time_sec - time_sec);
+ sec_downloaded = percent_to_sub * sec_downloaded;
+ *sec_to_download = percent_to_sub * *sec_to_download;
+
+ if ((sec_downloaded + *buffer) <= min_buffer)
+ rv = 1;
+ break;
+ }
+
+ if ((sec_downloaded + *buffer) <= min_buffer) {
+ rv = 1;
+ break;
+ }
+
+ desc_curr = get_cue_desc(s, desc_curr.end_time_ns, cues_start);
+ }
+ *buffer = *buffer + sec_downloaded;
+ return rv;
+}
+
+/* This function computes the bandwidth of the WebM file with the help of
+ * buffer_size_after_time_downloaded() function. Both of these functions are
+ * adapted from WebM Tools project and are adapted to work with FFmpeg's
+ * Matroska parsing mechanism.
+ * See:
+ * https://chromium.googlesource.com/webm/webm-tools/+/master/shared/webm_file.cc
+ * for details about how this implementation works.
+ * Returns -1 on error.
+ * */
+static int64_t webm_dash_manifest_compute_bandwidth(AVFormatContext *s, int64_t cues_start)
+{
+ MatroskaDemuxContext *matroska = s->priv_data;
+ AVStream *st = s->streams[0];
+ double bandwidth = 0.0;
+ for (int i = 0; i < st->nb_index_entries; i++) {
+ int64_t prebuffer_ns = 1000000000;
+ int64_t time_ns = st->index_entries[i].timestamp * matroska->time_scale;
+ double nano_seconds_per_second = 1000000000.0;
+ int64_t prebuffered_ns = time_ns + prebuffer_ns;
+ double prebuffer_bytes = 0.0;
+ int64_t temp_prebuffer_ns = prebuffer_ns;
+ int64_t pre_bytes, pre_ns;
+ double pre_sec, prebuffer, bits_per_second;
+ CueDesc desc_beg = get_cue_desc(s, time_ns, cues_start);
+
+ // Start with the first Cue.
+ CueDesc desc_end = desc_beg;
+
+ // Figure out how much data we have downloaded for the prebuffer. This will
+ // be used later to adjust the bits per sample to try.
+ while (desc_end.start_time_ns != -1 && desc_end.end_time_ns < prebuffered_ns) {
+ // Prebuffered the entire Cue.
+ prebuffer_bytes += desc_end.end_offset - desc_end.start_offset;
+ temp_prebuffer_ns -= desc_end.end_time_ns - desc_end.start_time_ns;
+ desc_end = get_cue_desc(s, desc_end.end_time_ns, cues_start);
+ }
+ if (desc_end.start_time_ns == -1) {
+ // The prebuffer is larger than the duration.
+ return (matroska->duration * matroska->time_scale >= prebuffered_ns) ? -1 : 0;
+ }
+
+ // The prebuffer ends in the last Cue. Estimate how much data was
+ // prebuffered.
+ pre_bytes = desc_end.end_offset - desc_end.start_offset;
+ pre_ns = desc_end.end_time_ns - desc_end.start_time_ns;
+ pre_sec = pre_ns / nano_seconds_per_second;
+ prebuffer_bytes +=
+ pre_bytes * ((temp_prebuffer_ns / nano_seconds_per_second) / pre_sec);
+
+ prebuffer = prebuffer_ns / nano_seconds_per_second;
+
+ // Set this to 0.0 in case our prebuffer buffers the entire video.
+ bits_per_second = 0.0;
+ do {
+ int64_t desc_bytes = desc_end.end_offset - desc_beg.start_offset;
+ int64_t desc_ns = desc_end.end_time_ns - desc_beg.start_time_ns;
+ double desc_sec = desc_ns / nano_seconds_per_second;
+ double calc_bits_per_second = (desc_bytes * 8) / desc_sec;
+
+ // Drop the bps by the percentage of bytes buffered.
+ double percent = (desc_bytes - prebuffer_bytes) / desc_bytes;
+ double mod_bits_per_second = calc_bits_per_second * percent;
+
+ if (prebuffer < desc_sec) {
+ double search_sec =
+ (double)(matroska->duration * matroska->time_scale) / nano_seconds_per_second;
+
+ // Add 1 so the bits per second should be a little bit greater than file
+ // datarate.
+ int64_t bps = (int64_t)(mod_bits_per_second) + 1;
+ const double min_buffer = 0.0;
+ double buffer = prebuffer;
+ double sec_to_download = 0.0;
+
+ int rv = buffer_size_after_time_downloaded(prebuffered_ns, search_sec, bps,
+ min_buffer, &buffer, &sec_to_download,
+ s, cues_start);
+ if (rv < 0) {
+ return -1;
+ } else if (rv == 0) {
+ bits_per_second = (double)(bps);
+ break;
+ }
+ }
+
+ desc_end = get_cue_desc(s, desc_end.end_time_ns, cues_start);
+ } while (desc_end.start_time_ns != -1);
+ if (bandwidth < bits_per_second) bandwidth = bits_per_second;
+ }
+ return (int64_t)bandwidth;
+}
+
+static int webm_dash_manifest_cues(AVFormatContext *s)
+{
+ MatroskaDemuxContext *matroska = s->priv_data;
+ EbmlList *seekhead_list = &matroska->seekhead;
+ MatroskaSeekhead *seekhead = seekhead_list->elem;
+ char *buf;
+ int64_t cues_start, cues_end, before_pos, bandwidth;
+ int i;
+
+ // determine cues start and end positions
+ for (i = 0; i < seekhead_list->nb_elem; i++)
+ if (seekhead[i].id == MATROSKA_ID_CUES)
+ break;
+
+ if (i >= seekhead_list->nb_elem) return -1;
+
+ before_pos = avio_tell(matroska->ctx->pb);
+ cues_start = seekhead[i].pos + matroska->segment_start;
+ if (avio_seek(matroska->ctx->pb, cues_start, SEEK_SET) == cues_start) {
+ uint64_t cues_length = 0, cues_id = 0;
+ ebml_read_num(matroska, matroska->ctx->pb, 4, &cues_id);
+ ebml_read_length(matroska, matroska->ctx->pb, &cues_length);
+ cues_end = cues_start + cues_length + 11; // 11 is the offset of Cues ID.
+ }
+ avio_seek(matroska->ctx->pb, before_pos, SEEK_SET);
+
+ // parse the cues
+ matroska_parse_cues(matroska);
+
+ // cues start
+ buf = av_asprintf("%" PRId64, cues_start);
+ av_dict_set(&s->streams[0]->metadata, CUES_START, buf, 0);
+ av_free(buf);
+
+ // cues end
+ buf = av_asprintf("%" PRId64, cues_end);
+ av_dict_set(&s->streams[0]->metadata, CUES_END, buf, 0);
+ av_free(buf);
+
+ // bandwidth
+ bandwidth = webm_dash_manifest_compute_bandwidth(s, cues_start);
+ if (bandwidth < 0) return -1;
+ buf = av_asprintf("%" PRId64, bandwidth);
+ av_dict_set(&s->streams[0]->metadata, BANDWIDTH, buf, 0);
+ av_free(buf);
+
+ // check if all clusters start with key frames
+ buf = av_asprintf("%d", webm_clusters_start_with_keyframe(s));
+ av_dict_set(&s->streams[0]->metadata, CLUSTER_KEYFRAME, buf, 0);
+ av_free(buf);
+
+ // store cue point timestamps as a comma separated list for checking subsegment alignment in
+ // the muxer. assumes that each timestamp cannot be more than 20 characters long.
+ buf = av_malloc(s->streams[0]->nb_index_entries * 20 * sizeof(char));
+ strcpy(buf, "");
+ for (i = 0; i < s->streams[0]->nb_index_entries; i++) {
+ snprintf(buf, (i + 1) * 20 * sizeof(char),
+ "%s%" PRId64, buf, s->streams[0]->index_entries[i].timestamp);
+ if (i != s->streams[0]->nb_index_entries - 1)
+ strncat(buf, ",", sizeof(char));
+ }
+ av_dict_set(&s->streams[0]->metadata, CUE_TIMESTAMPS, buf, 0);
+ av_free(buf);
+
+ return 0;
+}
+
+static int webm_dash_manifest_read_header(AVFormatContext *s)
+{
+ char *buf;
+ int ret = matroska_read_header(s);
+ MatroskaTrack *tracks;
+ MatroskaDemuxContext *matroska = s->priv_data;
+ if (ret) {
+ av_log(s, AV_LOG_ERROR, "Failed to read file headers\n");
+ return -1;
+ }
+
+ // initialization range
+ buf = av_asprintf("%" PRId64, avio_tell(s->pb) - 5); // 5 is the offset of Cluster ID.
+ av_dict_set(&s->streams[0]->metadata, INITIALIZATION_RANGE, buf, 0);
+ av_free(buf);
+
+ // basename of the file
+ buf = strrchr(s->filename, '/');
+ if (buf == NULL) return -1; // TODO return correct value here
+ av_dict_set(&s->streams[0]->metadata, FILENAME, ++buf, 0);
+
+ // duration
+ buf = av_asprintf("%g", matroska->duration);
+ av_dict_set(&s->streams[0]->metadata, DURATION, buf, 0);
+ av_free(buf);
+
+ // track number
+ tracks = matroska->tracks.elem;
+ buf = av_asprintf("%" PRId64, tracks[0].num);
+ av_dict_set(&s->streams[0]->metadata, TRACK_NUMBER, buf, 0);
+ av_free(buf);
+
+ // parse the cues and populate Cue related fields
+ return webm_dash_manifest_cues(s);
+}
+
+static int webm_dash_manifest_read_packet(AVFormatContext *s, AVPacket *pkt)
+{
+ return AVERROR_EOF;
+}
+
AVInputFormat ff_matroska_demuxer = {
.name = "matroska,webm",
.long_name = NULL_IF_CONFIG_SMALL("Matroska / WebM"),
@@ -3078,3 +3431,12 @@ AVInputFormat ff_matroska_demuxer = {
.read_close = matroska_read_close,
.read_seek = matroska_read_seek,
};
+
+AVInputFormat ff_webm_dash_manifest_demuxer = {
+ .name = "webm_dash_manifest",
+ .long_name = NULL_IF_CONFIG_SMALL("WebM DASH Manifest"),
+ .priv_data_size = sizeof(MatroskaDemuxContext),
+ .read_header = webm_dash_manifest_read_header,
+ .read_packet = webm_dash_manifest_read_packet,
+ .read_close = matroska_read_close,
+};
--
2.0.0.526.g5318336
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