On 6/7/2023 10:36 AM, Dawid Kozinski/Multimedia (PLT) /SRPOL/Staff
Engineer/Samsung Electronics wrote:
-----Original Message-----
From: ffmpeg-devel <ffmpeg-devel-boun...@ffmpeg.org> On Behalf Of James
Almer
Sent: poniedziałek, 29 maja 2023 15:08
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH v23 04/10] avformat/evc_demuxer: Added
demuxer to handle reading EVC video files
On 5/26/2023 7:31 AM, Dawid Kozinski wrote:
+static int get_temporal_id(const uint8_t *bits, int bits_size) {
+ int temporal_id = 0;
+ short t = 0;
+
+ if (bits_size >= EVC_NALU_HEADER_SIZE) {
+ unsigned char *p = (unsigned char *)bits;
+ // forbidden_zero_bit
+ if ((p[0] & 0x80) != 0)
+ return -1;
+
+ for (int i = 0; i < EVC_NALU_HEADER_SIZE; i++)
+ t = (t << 8) | p[i];
I think this can be replaced with AV_RB16.
+
+ temporal_id = (t >> 6) & 0x0007;
+ }
+
+ return temporal_id;
+}
[...]
+static uint32_t read_nal_unit_length(const uint8_t *bits, int
+bits_size) {
+ uint32_t nalu_len = 0;
+
+ if (bits_size >= EVC_NALU_LENGTH_PREFIX_SIZE) {
+
+ int t = 0;
+ unsigned char *p = (unsigned char *)bits;
+
+ for (int i = 0; i < EVC_NALU_LENGTH_PREFIX_SIZE; i++)
+ t = (t << 8) | p[i];
AV_RB32.
+
+ nalu_len = t;
+ if (nalu_len == 0) // Invalid bitstream size
+ return 0;
+ }
+
+ return nalu_len;
+}
[...]
+static int evc_frame_merge_filter(AVBSFContext *bsf, AVPacket *out) {
+ EVCMergeContext *ctx = bsf->priv_data;
+ AVPacket *in = ctx->in;
+
+ int free_space = 0;
+ size_t nalu_size = 0;
+ uint8_t *nalu = NULL;
+ int au_end_found = 0;
+ int err;
+
+ err = ff_bsf_get_packet_ref(bsf, in);
+ if (err < 0)
+ return err;
+
+ nalu_size = read_nal_unit_length(in->data,
EVC_NALU_LENGTH_PREFIX_SIZE);
+ if(nalu_size <= 0) {
+ av_packet_unref(in);
+ return AVERROR_INVALIDDATA;
+ }
+
+ nalu = in->data + EVC_NALU_LENGTH_PREFIX_SIZE;
+ nalu_size = in->size - EVC_NALU_LENGTH_PREFIX_SIZE;
+
+ // NAL unit parsing needed to determine if end of AU was found
+ err = parse_nal_unit(nalu, nalu_size, bsf);
+ if (err < 0) {
+ av_log(bsf, AV_LOG_ERROR, "NAL Unit parsing error\n");
+ av_packet_unref(in);
+
+ return err;
+ }
+
+ au_end_found = end_of_access_unit_found(bsf);
+
+ free_space = ctx->au_buffer.capacity - ctx->au_buffer.data_size;
+ while( free_space < in->size ) {
+ ctx->au_buffer.capacity *= 2;
+ free_space = ctx->au_buffer.capacity -
+ ctx->au_buffer.data_size;
+
+ if(free_space >= in->size) {
+ ctx->au_buffer.data = av_realloc(ctx->au_buffer.data, ctx-
au_buffer.capacity);
+ }
+ }
+
+ memcpy(ctx->au_buffer.data + ctx->au_buffer.data_size, in->data,
+ in->size);
This is including the Annex-B's nal_unit_lenght value into the assembled
packet. I
assume libxevd expects this? Also, is it defined as part of the ISOBMFF
encapsulation? Patch 07/10 does not seem to strip it.
Could you expand on this topic?
What do you mean by "Patch 07/10 does not seem to strip it"?
Patch 7/10 expands the implementation of the MOV Muxer to support the EVC
stream.
The function ff_isom_write_evcc parses the received data, extracts NAL units
of types SPS, PPS, APS, SEI, and inserts their contents into the
corresponding elements of the arrays array, which is a component of the
EVCDecoderConfigurationRecord structure. Additionally, the
ff_isom_write_evcc function populates the relevant fields of the
EVCDecoderConfigurationRecord structure based on the parsed SPS NAL unit
data, and then calls the evcc_write function, which writes the
EVCDecoderConfigurationRecord to the stream.
It seems that I don't understand what's wrong with our implementation ( I
mean MOV muxer for EVC) and it seems I need your help in this matter. I need
an explanation of what's wrong and what should be done to fix the issue.
I mean the packets that go into ISOBMFF Sample, not the evcc atom. Is
the encapsulation supposed to include the nal_unit_length from Annex-B?
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