} else {
param.rc.i_vbv_max_bitrate = global_flags.x264_vbv_max_bitrate;
}
+ if (param.rc.i_vbv_max_bitrate > 0) {
+ // If the user wants VBV control to cap the max rate, it is
+ // also reasonable to assume that they are fine with the stream
+ // constantly being around that rate even for very low-complexity
+ // content; the obvious and extreme example being a static
+ // black picture.
+ //
+ // One would think it's fine to have low-complexity codec use
+ // less bitrate, but it seems to cause problems in practice;
+ // e.g. VLC seems to often drop the stream (similar to a buffer
+ // underrun) in such cases, but only when streaming from Nageru,
+ // not when reading a dump of the same stream from disk.
+ // I'm not 100% sure whether it's in VLC (possibly some buffering
+ // in the HTTP layer), in microhttpd or somewhere in Nageru itself,
+ // but it's a typical case of problems that can arise. Similarly,
+ // TCP's congestion control is not always fond of the rate staying
+ // low for a while and then rising quickly -- a variation on the same
+ // problem.
+ //
+ // We solve this by simply asking x264 to fill in dummy bits
+ // in these cases, so that the bitrate stays reasonable constant.
+ // It's a waste of bandwidth, but it makes things go much more
+ // smoothly in these cases. (We don't do it if VBV control is off
+ // in general, not the least because it makes no sense and x264
+ // thus ignores the parameter.)
+ param.rc.b_filler = 1;
+ }
// Occasionally players have problem with extremely low quantizers;
// be on the safe side. Shouldn't affect quality in any meaningful way.
param.rc.i_qp_min = 5;
- // TODO: more flags here, via x264_param_parse().
+ for (const string &str : global_flags.x264_extra_param) {
+ const size_t pos = str.find(',');
+ if (pos == string::npos) {
+ if (x264_param_parse(¶m, str.c_str(), nullptr) != 0) {
+ fprintf(stderr, "ERROR: x264 rejected parameter '%s'\n", str.c_str());
+ }
+ } else {
+ const string key = str.substr(0, pos);
+ const string value = str.substr(pos + 1);
+ if (x264_param_parse(¶m, key.c_str(), value.c_str()) != 0) {
+ fprintf(stderr, "ERROR: x264 rejected parameter '%s' set to '%s'\n",
+ key.c_str(), value.c_str());
+ }
+ }
+ }
x264_param_apply_profile(¶m, "high");