ffmpeg: Add -time_base option to hint the time base

Signed-off-by: Michael Bradshaw <mjbshaw@google.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

ffmpeg.c

@@ -2905,7 +2905,8 @@ static int init_output_stream_streamcopy(OutputStream *ost)
         return ret;
 
     // copy timebase while removing common factors
-    ost->st->time_base = av_add_q(av_stream_get_codec_timebase(ost->st), (AVRational){0, 1});
+    if (ost->st->time_base.num <= 0 || ost->st->time_base.den <= 0)
+        ost->st->time_base = av_add_q(av_stream_get_codec_timebase(ost->st), (AVRational){0, 1});
 
     // copy disposition
     ost->st->disposition = ist->st->disposition;
@@ -3330,7 +3331,8 @@ static int init_output_stream(OutputStream *ost, char *error, int error_len)
         }
 
         // copy timebase while removing common factors
-        ost->st->time_base = av_add_q(ost->enc_ctx->time_base, (AVRational){0, 1});
+        if (ost->st->time_base.num <= 0 || ost->st->time_base.den <= 0)
+            ost->st->time_base = av_add_q(ost->enc_ctx->time_base, (AVRational){0, 1});
         ost->st->codec->codec= ost->enc_ctx->codec;
     } else if (ost->stream_copy) {
         ret = init_output_stream_streamcopy(ost);

ffmpeg.h

@@ -224,6 +224,8 @@ typedef struct OptionsContext {
     int        nb_disposition;
     SpecifierOpt *program;
     int        nb_program;
+    SpecifierOpt *time_bases;
+    int        nb_time_bases;
 } OptionsContext;
 
 typedef struct InputFilter {

ffmpeg_opt.c

@@ -1231,7 +1231,7 @@ static OutputStream *new_output_stream(OptionsContext *o, AVFormatContext *oc, e
     OutputStream *ost;
     AVStream *st = avformat_new_stream(oc, NULL);
     int idx      = oc->nb_streams - 1, ret = 0;
-    const char *bsfs = NULL;
+    const char *bsfs = NULL, *time_base = NULL;
     char *next, *codec_tag = NULL;
     double qscale = -1;
     int i;
@@ -1308,6 +1308,17 @@ static OutputStream *new_output_stream(OptionsContext *o, AVFormatContext *oc, e
         ost->encoder_opts = filter_codec_opts(o->g->codec_opts, AV_CODEC_ID_NONE, oc, st, NULL);
     }
 
+    MATCH_PER_STREAM_OPT(time_bases, str, time_base, oc, st);
+    if (time_base) {
+        AVRational q;
+        if (av_parse_ratio(&q, time_base, INT_MAX, 0, NULL) < 0 ||
+            q.num <= 0 || q.den <= 0) {
+            av_log(NULL, AV_LOG_FATAL, "Invalid time base: %s\n", time_base);
+            exit_program(1);
+        }
+        st->time_base = q;
+    }
+
     ost->max_frames = INT64_MAX;
     MATCH_PER_STREAM_OPT(max_frames, i64, ost->max_frames, oc, st);
     for (i = 0; i<o->nb_max_frames; i++) {
@@ -3649,6 +3660,9 @@ const OptionDef options[] = {
     { "sdp_file", HAS_ARG | OPT_EXPERT | OPT_OUTPUT, { .func_arg = opt_sdp_file },
         "specify a file in which to print sdp information", "file" },
 
+    { "time_base", HAS_ARG | OPT_STRING | OPT_EXPERT | OPT_SPEC | OPT_OUTPUT, { .off = OFFSET(time_bases) },
+        "set the desired time base hint for output stream (1:24, 1:48000 or 0.04166, 2.0833e-5)", "ratio" },
+
     { "bsf", HAS_ARG | OPT_STRING | OPT_SPEC | OPT_EXPERT | OPT_OUTPUT, { .off = OFFSET(bitstream_filters) },
         "A comma-separated list of bitstream filters", "bitstream_filters" },
     { "absf", HAS_ARG | OPT_AUDIO | OPT_EXPERT| OPT_PERFILE | OPT_OUTPUT, { .func_arg = opt_old2new },