dashenc: Add options to make segment names configurable

This allows one to specify templated segment names for init-segments,
media-segments, and for the base-url in the case of single-file.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/dashenc.c

@@ -38,6 +38,16 @@
 #include "os_support.h"
 #include "url.h"
 
+// See ISO/IEC 23009-1:2014 5.3.9.4.4
+typedef enum {
+    DASH_TMPL_ID_UNDEFINED = -1,
+    DASH_TMPL_ID_ESCAPE,
+    DASH_TMPL_ID_REP_ID,
+    DASH_TMPL_ID_NUMBER,
+    DASH_TMPL_ID_BANDWIDTH,
+    DASH_TMPL_ID_TIME,
+} DASHTmplId;
+
 typedef struct Segment {
     char file[1024];
     int64_t start_pos;
@@ -59,6 +69,7 @@ typedef struct OutputStream {
     int nb_segments, segments_size, segment_index;
     Segment **segments;
     int64_t first_dts, start_dts, end_dts;
+    int bit_rate;
     char bandwidth_str[64];
 
     char codec_str[100];
@@ -79,6 +90,9 @@ typedef struct DASHContext {
     int total_duration;
     char availability_start_time[100];
     char dirname[1024];
+    const char *single_file_name;
+    const char *init_seg_name;
+    const char *media_seg_name;
 } DASHContext;
 
 static int dash_write(void *opaque, uint8_t *buf, int buf_size)
@@ -192,7 +206,7 @@ static void output_segment_list(OutputStream *os, AVIOContext *out, DASHContext
         avio_printf(out, "\t\t\t\t<SegmentTemplate timescale=\"%d\" ", timescale);
         if (!c->use_timeline)
             avio_printf(out, "duration=\"%d\" ", c->last_duration);
-        avio_printf(out, "initialization=\"init-stream$RepresentationID$.m4s\" media=\"chunk-stream$RepresentationID$-$Number%%05d$.m4s\" startNumber=\"%d\">\n", c->use_timeline ? start_number : 1);
+        avio_printf(out, "initialization=\"%s\" media=\"%s\" startNumber=\"%d\">\n", c->init_seg_name, c->media_seg_name, c->use_timeline ? start_number : 1);
         if (c->use_timeline) {
             avio_printf(out, "\t\t\t\t\t<SegmentTimeline>\n");
             for (i = start_index; i < os->nb_segments; ) {
@@ -235,6 +249,120 @@ static void output_segment_list(OutputStream *os, AVIOContext *out, DASHContext
     }
 }
 
+static DASHTmplId dash_read_tmpl_id(const char *identifier, char *format_tag,
+                                    size_t format_tag_size, const char **ptr) {
+    const char *next_ptr;
+    DASHTmplId id_type = DASH_TMPL_ID_UNDEFINED;
+
+    if (av_strstart(identifier, "$$", &next_ptr)) {
+        id_type = DASH_TMPL_ID_ESCAPE;
+        *ptr = next_ptr;
+    } else if (av_strstart(identifier, "$RepresentationID$", &next_ptr)) {
+        id_type = DASH_TMPL_ID_REP_ID;
+        // default to basic format, as $RepresentationID$ identifiers
+        // are not allowed to have custom format-tags.
+        av_strlcpy(format_tag, "%d", format_tag_size);
+        *ptr = next_ptr;
+    } else { // the following identifiers may have an explicit format_tag
+        if (av_strstart(identifier, "$Number", &next_ptr))
+            id_type = DASH_TMPL_ID_NUMBER;
+        else if (av_strstart(identifier, "$Bandwidth", &next_ptr))
+            id_type = DASH_TMPL_ID_BANDWIDTH;
+        else if (av_strstart(identifier, "$Time", &next_ptr))
+            id_type = DASH_TMPL_ID_TIME;
+        else
+            id_type = DASH_TMPL_ID_UNDEFINED;
+
+        // next parse the dash format-tag and generate a c-string format tag
+        // (next_ptr now points at the first '%' at the beginning of the format-tag)
+        if (id_type != DASH_TMPL_ID_UNDEFINED) {
+            const char *number_format = DASH_TMPL_ID_TIME ? "lld" : "d";
+            if (next_ptr[0] == '$') { // no dash format-tag
+                snprintf(format_tag, format_tag_size, "%%%s", number_format);
+                *ptr = &next_ptr[1];
+            } else {
+                const char *width_ptr;
+                // only tolerate single-digit width-field (i.e. up to 9-digit width)
+                if (av_strstart(next_ptr, "%0", &width_ptr) &&
+                    av_isdigit(width_ptr[0]) &&
+                    av_strstart(&width_ptr[1], "d$", &next_ptr)) {
+                    // yes, we're using a format tag to build format_tag.
+                    snprintf(format_tag, format_tag_size, "%s%c%s", "%0", width_ptr[0], number_format);
+                    *ptr = next_ptr;
+                } else {
+                    av_log(NULL, AV_LOG_WARNING, "Failed to parse format-tag beginning with %s. Expected either a "
+                                                 "closing '$' character or a format-string like '%%0[width]d', "
+                                                 "where width must be a single digit\n", next_ptr);
+                    id_type = DASH_TMPL_ID_UNDEFINED;
+                }
+            }
+        }
+    }
+    return id_type;
+}
+
+static void dash_fill_tmpl_params(char *dst, size_t buffer_size,
+                                  const char *template, int rep_id,
+                                  int number, int bit_rate,
+                                  int64_t time) {
+    int dst_pos = 0;
+    const char *t_cur = template;
+    while (dst_pos < buffer_size - 1 && *t_cur) {
+        int format_tag_size = 7;
+        char format_tag[format_tag_size]; // May be "%d", "%0Xd", or "%0Xlld" (for $Time$), where X is in [0-9]
+        int n = 0;
+        DASHTmplId id_type;
+        const char *t_next = strchr(t_cur, '$'); // copy over everything up to the first '$' character
+        if (t_next) {
+            int num_copy_bytes = FFMIN(t_next - t_cur, buffer_size - dst_pos - 1);
+            av_strlcpy(&dst[dst_pos], t_cur, num_copy_bytes + 1);
+            // advance
+            dst_pos += num_copy_bytes;
+            t_cur = t_next;
+        } else { // no more DASH identifiers to substitute - just copy the rest over and break
+            av_strlcpy(&dst[dst_pos], t_cur, buffer_size - dst_pos);
+            break;
+        }
+
+        if (dst_pos >= buffer_size - 1 || !*t_cur)
+            break;
+
+        // t_cur is now pointing to a '$' character
+        id_type = dash_read_tmpl_id(t_cur, format_tag, format_tag_size, &t_next);
+        switch (id_type) {
+        case DASH_TMPL_ID_ESCAPE:
+            av_strlcpy(&dst[dst_pos], "$", 2);
+            n = 1;
+            break;
+        case DASH_TMPL_ID_REP_ID:
+            n = snprintf(&dst[dst_pos], buffer_size - dst_pos, format_tag, rep_id);
+            break;
+        case DASH_TMPL_ID_NUMBER:
+            n = snprintf(&dst[dst_pos], buffer_size - dst_pos, format_tag, number);
+            break;
+        case DASH_TMPL_ID_BANDWIDTH:
+            n = snprintf(&dst[dst_pos], buffer_size - dst_pos, format_tag, bit_rate);
+            break;
+        case DASH_TMPL_ID_TIME:
+            n = snprintf(&dst[dst_pos], buffer_size - dst_pos, format_tag, time);
+            break;
+        case DASH_TMPL_ID_UNDEFINED:
+            // copy over one byte and advance
+            av_strlcpy(&dst[dst_pos], t_cur, 2);
+            n = 1;
+            t_next = &t_cur[1];
+            break;
+        }
+        // t_next points just past the processed identifier
+        // n is the number of bytes that were attempted to be written to dst
+        // (may have failed to write all because buffer_size).
+
+        // advance
+        dst_pos += FFMIN(n, buffer_size - dst_pos - 1);
+        t_cur = t_next;
+    }
+}
+
 static char *xmlescape(const char *str) {
     int outlen = strlen(str)*3/2 + 6;
     char *out = av_realloc(NULL, outlen + 1);
@@ -403,6 +531,8 @@ static int dash_write_header(AVFormatContext *s)
     char *ptr;
     char basename[1024];
 
+    if (c->single_file_name)
+        c->single_file = 1;
     if (c->single_file)
         c->use_template = 0;
 
@@ -439,9 +569,10 @@ static int dash_write_header(AVFormatContext *s)
         AVDictionary *opts = NULL;
         char filename[1024];
 
-        if (s->streams[i]->codec->bit_rate) {
+        os->bit_rate = s->streams[i]->codec->bit_rate;
+        if (os->bit_rate) {
             snprintf(os->bandwidth_str, sizeof(os->bandwidth_str),
-                     " bandwidth=\"%d\"", s->streams[i]->codec->bit_rate);
+                     " bandwidth=\"%d\"", os->bit_rate);
         } else {
             int level = s->strict_std_compliance >= FF_COMPLIANCE_STRICT ?
                         AV_LOG_ERROR : AV_LOG_WARNING;
@@ -476,10 +607,14 @@ static int dash_write_header(AVFormatContext *s)
             goto fail;
         }
 
-        if (c->single_file)
-            snprintf(os->initfile, sizeof(os->initfile), "%s-stream%d.m4s", basename, i);
-        else
-            snprintf(os->initfile, sizeof(os->initfile), "init-stream%d.m4s", i);
+        if (c->single_file) {
+            if (c->single_file_name)
+                dash_fill_tmpl_params(os->initfile, sizeof(os->initfile), c->single_file_name, i, 0, os->bit_rate, 0);
+            else
+                snprintf(os->initfile, sizeof(os->initfile), "%s-stream%d.m4s", basename, i);
+        } else {
+            dash_fill_tmpl_params(os->initfile, sizeof(os->initfile), c->init_seg_name, i, 0, os->bit_rate, 0);
+        }
         snprintf(filename, sizeof(filename), "%s%s", c->dirname, os->initfile);
         ret = ffurl_open(&os->out, filename, AVIO_FLAG_WRITE, &s->interrupt_callback, NULL);
         if (ret < 0)
@@ -624,7 +759,7 @@ static int dash_flush(AVFormatContext *s, int final, int stream)
         }
 
         if (!c->single_file) {
-            snprintf(filename, sizeof(filename), "chunk-stream%d-%05d.m4s", i, os->segment_index);
+            dash_fill_tmpl_params(filename, sizeof(filename), c->media_seg_name, i, os->segment_index, os->bit_rate, os->start_dts);
             snprintf(full_path, sizeof(full_path), "%s%s", c->dirname, filename);
             snprintf(temp_path, sizeof(temp_path), "%s.tmp", full_path);
             ret = ffurl_open(&os->out, temp_path, AVIO_FLAG_WRITE, &s->interrupt_callback, NULL);
@@ -769,6 +904,9 @@ static const AVOption options[] = {
     { "use_template", "Use SegmentTemplate instead of SegmentList", OFFSET(use_template), AV_OPT_TYPE_INT, { .i64 = 1 }, 0, 1, E },
     { "use_timeline", "Use SegmentTimeline in SegmentTemplate", OFFSET(use_timeline), AV_OPT_TYPE_INT, { .i64 = 1 }, 0, 1, E },
     { "single_file", "Store all segments in one file, accessed using byte ranges", OFFSET(single_file), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 1, E },
+    { "single_file_name", "DASH-templated name to be used for baseURL. Implies storing all segments in one file, accessed using byte ranges", OFFSET(single_file_name), AV_OPT_TYPE_STRING, { .str = NULL }, 0, 0, E },
+    { "init_seg_name", "DASH-templated name to used for the initialization segment", OFFSET(init_seg_name), AV_OPT_TYPE_STRING, {.str = "init-stream$RepresentationID$.m4s"},  0, 0, E },
+    { "media_seg_name", "DASH-templated name to used for the media segments", OFFSET(media_seg_name), AV_OPT_TYPE_STRING, {.str = "chunk-stream$RepresentationID$-$Number%05d$.m4s"},  0, 0, E },
     { NULL },
 };